This is the accepted version of the article: De Jaime-Soguero, Chabier; Mujal, Eudald; Dinarès-Turell, Jaume; [et al.]. «Palaeoecology of Middle Triassic tetrapod ichnoassociations (middle Muschel- kalk, NE Iberian Peninsula) and their implications for palaeobiogeography in the western Tethys region». Palaeogeography, palaeoclimatology, palaeoecology, Vol. 565 (March 2021), art. 110204. DOI 10.1016/j.palaeo.2020.110204 This version is available at https://ddd.uab.cat/record/237257 under the terms of the license 1 Palaeoecology of Middle Triassic tetrapod ichnoassociations (middle Muschelkalk, 2 NE Iberian Peninsula) and their implications for palaeobiogeography in the 3 western Tethys region 4 5 Chabier De Jaime-Sogueroa,1, Eudald Mujalb,a,1,*, Jaume Dinarès-Turellc, Oriol Omsd, 6 Arnau Boleta,e, Guillem Orlandi-Oliverasa, Josep Fortunya,* 7 8 (a) Institut Català de Paleontologia Miquel Crusafont, Universitat Autònoma de 9 Barcelona, ICTA-ICP building, c/de les columnes s/n, Campus de la UAB, E-08193 10 Cerdanyola del Vallès, Catalonia, Spain 11 (b) Staatliches Museum für Naturkunde Stuttgart, Rosenstein 1, D-70191 Stuttgart, 12 Germany 13 (c) Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, I-00143 14 Roma, Italy 15 (d) Departament de Geologia, Universitat Autònoma de Barcelona, E-08193 Bellaterra, 16 Catalonia, Spain 17 (e) School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens 18 Road, Bristol BS8 1RJ, United Kingdom. 19 20 (1) These authors contributed equally to this work 21 *Corresponding authors: eudald.mujalgrane@smns-bw.de (E. Mujal), 22 josep.fortuny@icp.cat (J. Fortuny) 23 24 Abstract 25 Tetrapod ichnology is a powerful tool to reconstruct the faunal composition of Middle 26 Triassic ecosystems. However, reconstructions based on a single palaeoenvironment 27 provide an incomplete and impoverished picture of the actual palaeodiversity. In this 28 paper, we analyse Middle Triassic tetrapod ichnoassociations from the detrital 29 Muschelkalk facies of the Catalan Basin of northeast Spain, ranging from terrestrial to 30 coastal settings. We identified two main tetrapod ichnoassociations, preserved in two 31 different palaeoenvironments, comprising the following ichnogenera and morphotypes: 32 Procolophonichnium, Chelonipus, Rhynchosauroides, Rotodactylus, Chirotherium, 33 Isochirotherium, Sphingopus, and indeterminate chirotheriids. We also statistically 34 analyse a database of all known Middle Triassic tetrapod footprint localities worldwide; 1 35 this database includes, for each track locality, the precise age, the palaeoenvironment 36 and the presence/absence of ichnotaxa. Our results on the composition of ichnofauna 37 within the palaeoenvironments of the Catalan Basin are integrated into this database. 38 This approach allows us to revisit the palaeoenvironmental bias linked to the marine 39 transgression that affected the Western Tethys region. Tetrapod ichnoassociations reveal 40 the following palaeoenvironmental patterns: (1) in coastal settings, ichnoassociations 41 are Rhynchosauroides-dominated and diversity is relatively low; (2) in terrestrial 42 settings and those with less marine influences, ichnoassociations are non- 43 Rhynchosauroides-dominated, usually characterised by more abundant chirotheriid 44 tracks and, generally, a higher track diversity. The correlation between tetrapod 45 ichnoassociations and sedimentary facies reveals how palaeoenvironmental constraints 46 influenced faunal assemblages, especially those of the Middle Triassic of the Western 47 Tethys region. Ichnoassociations allow the ecological response of tetrapod faunas to the 48 environmental changes to be inferred for this critical time interval. Marine 49 transgressions strongly influenced tetrapod ecosystems: environmental conditions were 50 key for the faunal recovery in the aftermath of the end-Permian extinction, with the 51 settlement of the so-called modern faunas and the rise of the dinosaur lineage. 52 53 Keywords 54 tetrapod footprints; palaeoenvironments; coastal settings; Anisian; Ladinian; equatorial 55 Pangaea 56 57 1. Introduction 58 The Triassic period is characterised by recovery in the aftermath of the most 59 severe biotic crisis of Earth history, the end-Permian mass extinction, which led to the 60 origin of so-called modern ecosystems (Benton, 2016). However, the complete faunal 61 recovery was delayed until the Middle Triassic due to the harsh environmental 62 conditions (Irmis and Whiteside, 2012), especially in equatorial Pangaea (Sun et al., 63 2012; Benton and Newell, 2014; Benton, 2018). While in the marine realm the severity 64 of the biotic crisis and subsequent recovery are relatively well understood, the 65 magnitude of the event is still uncertain for the continental ecosystems, especially 66 considering vertebrates (Lucas, 2017, 2018). The Middle Triassic continental vertebrate 67 faunas globally present a relatively high diversity, with the radiation of newly 68 successful diapsid groups (Ezcurra, 2010), the lineages of which most probably 2 69 appeared during the late Palaeozoic (Simões et al., 2018; Bernardi et al., 2019). On the 70 one hand, the Lower–Middle Triassic tetrapod record from middle-high palaeolatitudes 71 is particularly well-known, based on the great sampling efforts performed in South 72 Africa and Russia, which reveal that these ecosystems were characterised by abundant 73 temnospondyl amphibians, as well as therapsids, being neodiapsid reptiles present, but 74 less abundant (Lucas, 2010; Romano et al., 2020, and references therein). On the other 75 hand, Middle Triassic continental vertebrate faunas from equatorial Pangaea include 76 temnospondyl amphibians (e.g., capitosaurids and plagiosaurids) and a high diversity of 77 reptiles ranging from terrestrial to semi-aquatic and aquatic habitats (Sues and Fraser, 78 2010). Dominant diapsid reptiles (particularly archosauromorphs) coexisted with 79 procolophonid parareptiles, stem-turtles, lepidosauromorphs and a few cynodonts 80 (Schoch and Milner, 2000; Damiani et al., 2009; Ezcurra, 2010; Schoch and Sues, 2015, 81 2018; Schoch et al., 2018; Simões et al., 2018). Environmental changes through time, 82 including a greater marine influence, are reflected by coastal and marine vertebrate 83 faunas, such as tanystropheids (e.g., Macrocnemus and Tanystropheus), stem turtles, 84 ichthyosauriforms, thalattosaurians, sauropterygians (e.g., pachypleurosaurs, 85 nothosaurians and placodonts), saurosphargids, as well as fish faunas (actinopterygians 86 and sarcopterygians) (Rieppel and Hagdorn, 1998; Rieppel, 2000; Ezcurra, 2010; Xing 87 et al., 2020). Terrestrial ecosystems and the role of their faunas are far from being fully 88 understood because of the small number of sites, although some exceptional Fossil- 89 Lagerstätten localities exist (Schoch and Seegis, 2016). In fact, the number of terrestrial 90 taxa from Middle Triassic low-latitude localities is generally sparse (Lucas, 2010; 91 Fortuny et al., 2011a). 92 The skeletal information of Middle Triassic terrestrial faunas is complemented 93 by a notably richer tetrapod ichnological record. Continental Middle Triassic vertebrate 94 footprints are globally recorded (Fig. 1) in many palaeoenvironments ranging from 95 inland fluvial and lacustrine settings to coastal (shores, lagoons, tidal flats) and shallow 96 marine settings (Table S1). Therefore, ichnofaunal diversity may broadly reflect the 97 habitat preferences of vertebrates, as well as environmental changes through space and 98 time, as it is observed in other time intervals (Mujal et al., 2016a, 2017a, 2017b; 99 Bernardi et al., 2018; Marchetti et al., 2019a). In fact, tetrapod footprints are useful tools 100 in palaeoenvironmental analyses (Melchor and Sarjeant, 2004; Hunt and Lucas, 2007a, 101 2007b; Diedrich, 2008; Melchor, 2015; Marchetti et al., 2017, 2019b; Mujal et al., 102 2018a; Schneider et al., 2020). Noteworthy, biases in the ichnofaunal record also exist, 3 103 as is the case for the Triassic amphibian temnospondyl record, with abundant bones and 104 scarce footprints (Klein and Lucas, 2010a; Marsicano et al., 2014; Mujal and Schoch, 105 2020; Farman and Bell, 2020; Schneider et al., 2020). 106 Important changes took place during the Middle Triassic in the western peri- 107 Tethys region: most of the earliest Triassic terrestrial ecosystems of the central-eastern 108 part of Pangaea (nowadays Europe and northern Africa) evolved to coastal-marine 109 environments (Bourquin et al., 2011). This was due to the marine transgression that 110 affected most of the European and North-African basins (Escudero-Mozo et al., 2015; 111 Franz et al., 2015) (Fig. 1). This transgression was not coeval in all these basins as 112 revealed by the diachronic nature of the facies (López-Gómez et al., 2002; Franz et al., 113 2013, 2015; Ortí et al., 2017, 2018; Maron et al., 2019), resulting in diachronous faunal 114 changes. The record of Middle Triassic vertebrate footprints from the Western peri- 115 Tethys basins is significantly abundant (Fig. 1; Table S1), with localities known from 116 Spain (Demathieu et al., 1978; Pérez-López, 1993; Gand et al., 2010; Fortuny et al., 117 2011a; Díaz-Martínez et al., 2015; Mujal et al., 2015, 2018a; Reolid and Reolid, 2017; 118 Berrocal-Casero et al., 2018a, 2018b; Reolid et al., 2020), Morocco (Klein et al., 2011), 119 Algeria (Kotański et al., 2004), Tunisia (Niedźwiedzki et al., 2017), France (Demathieu 120 and Demathieu, 2004; Gand et al., 2007, and references therein), Italy (Avanzini and 121 Mietto, 2008; Avanzini et al., 2011; Citton et al. 2020; Mietto et al., 2020, and 122 references therein), Switzerland (Klein et al., 2016; Cavin and Piuz, 2020, and 123 references therein), the Netherlands (Demathieu and Oosterink, 1983, 1988; Diedrich, 124 2002, 2008; Marchetti et al., 2019c) and Germany (e.g., Haubold, 1971a, 1971b, 1984; 125 Haubold and Klein, 2002; Diedrich, 2008, 2012; Klein et al., 2015; Klein and Lucas, 126 2018; Marchetti et al., 2020; Mujal and Schoch, 2020). 127 In order to understand the relationship of Middle Triassic vertebrate faunas, in 128 particular those from the Western Tethys, with the palaeoenvironment, we provide a 129 detailed analysis of the ichnological record from the middle Muschelkalk unit of the 130 Catalan Basin (NE Iberian Peninsula). Such unit corresponds to a coastal and distal 131 alluvial succession embedded within the two (lower and upper) Muschelkalk marine 132 carbonate units (Calvet and Marzo, 1994; see section 2 below). So far, Muschelkalk 133 terrestrial ichnoassemblages from the Iberian Peninsula are scanty (Fortuny et al., 134 2011a), only known from two middle Muschelkalk sites from the Catalan Basin (Mujal 135 et al., 2015, 2018a), and two additional Muschelkalk sites from the Iberian Ranges 136 (Demathieu et al., 1987; Berrocal-Casero et al., 2018a, 2018b). This work significantly 4 137 enlarges the knowledge of the Middle Triassic vertebrate ichnofaunas from the Iberian 138 Peninsula by describing three new ichnosites. 139 As a whole, we pursue to understand tetrapod palaeoecology on the basis of the 140 ichnological record, i.e., how palaeoenvironments constrain the distribution of 141 ichnotaxa, either prompting an abundant presence or the complete absence of specific 142 ichnotaxa (e.g., Diedrich, 2008; Melchor, 2015; Mujal et al., 2018a). Additionally, 143 because sea level fluctuations caused strong changes on these ecosystems, the present 144 work sheds light on the vertebrate footprint palaeoecology according to: (1) the newly 145 discovered tetrapod ichnoassemblages, in relation to their stratigraphic and 146 sedimentological setting, from the Catalan Basin (Texts S1 and S2); (2) the Western 147 Tethys tetrapod ichnological record. The integrated review of Middle Triassic tetrapod 148 tracks and corresponding palaeoenvironments sheds light on the evolution of a key time 149 interval for the tetrapod evolution in an area, the equatorial Pangaea, in which the 150 skeletal record is scanty. 151 152 2. Geological setting 153 154 During the Middle Triassic, the Iberian plate was situated in the western peri- 155 Tethys, eastern part of Pangaea, equatorial latitudes (Fig. 1). The Catalan Coastal 156 Ranges (CCR, NE Iberian Peninsula; Fig. 2) were a depressed, tectonically controlled 157 zone (a rift system) known as the Catalan Basin, corresponding to the north-eastern 158 region of the Iberian plate (Marzo, 1980). The CCR evolved as a NE-SW oriented rift 159 with conjugate NW-SE fault systems (Galán-Abellán et al., 2013). During this time 160 interval, all western peri-Tethys basins were intersected by marine transgressions 161 (occurring at different times as indicated by the diachronic facies at European scale) that 162 resulted in the formation of shallow epicontinental sea areas (Escudero-Mozo et al., 163 2015; Ortí et al., 2017). 164 As regards the Iberian plate, the Early to early Middle Triassic terrestrial 165 ecosystems are represented by the siliciclastic Buntsandstein red-beds facies mostly 166 corresponding to alluvial and fluvial deposits (e.g., Dinarès-Turell et al., 2005; 167 Bourquin et al., 2011; Fortuny et al., 2011b; Galán-Abellán et al., 2013; Mujal et al., 168 2016b, 2017a, 2017b). These facies were gradually replaced by shallow marine 169 environments from East to West, represented by the carbonate and evaporitic 170 Muschelkalk facies (Escudero-Mozo et al., 2015). During the Anisian–Ladinian 5 171 transition, a short regression episode took place in eastern Iberian plate, leading the 172 marine areas of the Catalan Basin to evolve to coastal environments, such as tidal mud 173 flats, sabkhas and distal floodplains (Calvet and Marzo, 1994; Ortí et al., 2017, 2018). 174 Later, a new transgression took place, affecting most parts of Iberia during the Ladinian 175 (Escudero-Mozo et al., 2015) (Fig. 1). In the sedimentary record, the 176 palaeoenvironments of the regression interval are represented by detrital deposits 177 composed of mudstone and sandstone red-beds with gypsum and limestone/dolostone 178 intervals between the two carbonate units of the Muschelkalk facies (Calvet and Marzo, 179 1994; Morad et al., 1995; Mujal et al., 2015, 2018a; Ortí et al., 2018). Thus, in the 180 Catalan Basin, three Muschelkalk (informal) units are well-differentiated: lower, middle 181 and upper Muschelkalk facies. 182 The thickness of the Triassic (Buntsandstein, Muschelkalk and Keuper) 183 successions of the Catalan Basin ranges from 500 to 800 m (Calvet et al., 1990). The 184 Middle Triassic Muschelkalk successions are arranged in three different domains, from 185 SW to NE: Priorat-Baix Ebre, Prades and Gaià-Monsteny (Marzo, 1980). The newly 186 herein reported tetrapod footprint localities, as well as those studied by Mujal et al. 187 (2015, 2018a) are all found in the Gaià-Montseny domain. The middle Muschelkalk 188 facies successions, which in several areas are highly affected by alpine tectonics 189 deformations, present an average thickness of about 100 m (Calvet and Marzo, 1994) 190 (Fig. 2). These facies are dated as late Anisian–middle Ladinian based on palynomorph 191 and conodont biostratigraphy (Solé de Porta et al., 1987; Márquez-Aliaga et al., 2000). 192 The middle Muschelkalk facies consist of a mixed succession of siliciclastic, carbonate 193 and evaporitic lithologies. According to Ortí et al. (2018), the succession can be divided 194 in three main basin-scale units: Lower (Paüls Gypsum), Middle (Arbolí Gypsum/Guanta 195 Sandstone) and Upper (Camposines Gypsum). For the detailed descriptions of each unit, 196 especially regarding the evaporitic content, see Morad et al. (1995) and Ortí et al. 197 (2018). The stratigraphic and sedimentological framework for the published (Mujal et 198 al., 2015, 2018a) and new track-bearing successions are described and discussed in 199 sections 4.1 and 5.1 below and Texts S1 and S3. All the tetrapod footprint localities 200 correspond to the Middle Unit of the middle Muschelkalk, specifically to the Arbolí 201 Gypsum and/or the Guanta Sandstone, within the Gaià-Montseny domain. In this 202 domain, according to Ortí et al. (2018): 203 1) The Arbolí Gypsum, mainly corresponding to the lowermost part of the Middle 204 Unit, is a succession of massive, laminated and/or nodular gypsum alternated with 6 205 red mudstones and discrete greyish dolostone intervals. It is interpreted as “an 206 extensive, evaporitic, red mudflat lodging a mosaic of shallow salinas and sabkhas 207 fed by marine water. This evaporitic mudflat was sensitive to record depositional 208 cyclicity of high-frequency” (Ortí et al., 2018:167). 209 2) The Guanta Sandstone, encompassing most of the Middle Unit, consists of a mainly 210 cyclic red-bed siliciclastic succession of fine- to medium-grained sandstones 211 alternated with mudstones. The sedimentary setting is interpreted as “midfan 212 distributive channels and floodplains of ephemeral streams in sandy alluvial fans” 213 (Ortí et al., 2018:172). As described and discussed (see sections 4.1 and 5.1 below 214 and Texts S1 and S3), these deposits were also influenced by salty waters. 215 216 3. Material and methods 217 218 A total of five middle Muschelkalk tetrapod footprint localities from the Catalan 219 Coastal Ranges (NE Iberian Peninsula) are here analysed, together with reference 220 sections by Ortí et al. (2018) (Fig. 2). The track-bearing localities are named, from 221 south to north and west to east (according to their position within the Catalan Basin), as 222 follows: Penya Rubí – new locality (Vallirana, Baix Llobregat), Puigventós – new 223 locality (Vacarisses, Vallès Occidental), Collcardús (Vacarisses, Vallès Occidental; 224 from Mujal et al., 2015), Pedrera de Can Sallent (Castellar del Vallès, Vallès 225 Occidental; from Mujal et al., 2018a), Montmany – historical finding and new locality 226 (Figaró-Montmany, Vallès Oriental). 227 While carrying out the palaeontological prospections, stratigraphic sections have 228 been measured by means of a Jacobs staff and a measuring tape (when possible, as some 229 outcrops are highly tectonised, see below). Some X-ray diffractions were carried out to 230 check dolomite content in dolostones from Penya Rubí. The stratigraphic position and 231 the GPS coordinates of the footprint-bearing localities have also been recorded. The 232 exact geographic and stratigraphic origin of the historical finding from the Montmany is 233 unknown. However, this area has been recently prospected, and several layers bearing 234 tetrapod footprints, as well as ex situ track-bearing slabs, have been discovered. The 235 historic specimen of Montmany, a previously unpublished sandstone slab bearing 236 several tetrapod ichnites in convex hyporelief, was located in the fossil collections of 237 the University of Montpellier (France) in 2014 by one of the authors (EM). It has a label 238 from the Museu Geològic del Seminari of Barcelona (MGSB) with catalogue number 7 239 26310; the label indicates that it was donated in 1975 to the Montpellier institution. In 240 this regard, under the corresponding permits, it was returned to the MGSB in 2018. 241 The new trace fossils recovered from Penya Rubí, Puigventós and Montmany 242 were consolidated for proper conservation with ethyl silicate when necessary, and are 243 stored at the Institut Català de Paleontologia Miquel Crusafont (ICP, Sabadell, 244 Catalonia, Spain). Descriptions and measurements follow the conventions of Haubold 245 (1971a, 1971b) and Leonardi (1987). The specimens used for the ichnotaxonomic 246 assignments are those with a higher degree of morphological preservation (see 247 Marchetti et al., 2019b). Skin impressions preserved in some of the herein analysed 248 footprints are also described in detail and compared to those reported in the literature. 249 Selected ichnites were digitised to obtain 3D models using photogrammetry technique. 250 Photographs were obtained using a digital reflex camera Nikon D3200, with an 251 objective AF-S Nikkor 15-55 mm 1:3.5-5.6 GII and following the procedures of 252 Falkingham (2012) and Mallison and Wings (2014). 3D models were processed with 253 different softwares, following the procedures of Mujal et al. (2016a, 2020): Agisoft 254 Photoscan (standard v.1.1.4) to generate the dense point cloud and the mesh, MeshLab 255 (v.2016.12 and v.2020.07) to edit the mesh (cleaning, scale and orientation) and 256 ParaView (v.4.1.0) to generate colour depth maps and contours. 257 A database of the worldwide known Middle Triassic tetrapod tracksites has also 258 been built (Table S1), including for each region/locality: age, inferred 259 palaeoenvironment and ichnotaxa present. Descriptive statistics have been performed 260 based on relative abundance (Tables S2, S3), counting presence (1) and absence (0) of 261 each ichnotaxon in the different palaeoenvironments. We calculated the percentages of 262 occurrence of each ichnotaxon, without considering the absolute number of footprints 263 from the analysed regions/localities. In this sense, the representativity of each 264 ichnotaxon in a certain setting is calculated by dividing its occurrences within that 265 palaeoenvironment by all the occurrences reported from this type of palaeoenvironment 266 (Table S2). Also, the percentage of occurrence of a specific ichnotaxon in a determinate 267 palaeoenvironment is calculated as its occurrences in a certain palaeoenvironment by 268 the number of localities assigned to this palaeoenvironment (Table S3). 269 Tetrapod ichnogenera are taken as the basic counting unit, because they are the 270 best defined ichnotaxonomic level, though some exceptions are also considered. Less 271 precisely identified trace fossils are also counted, because some tetrapod trace 272 morphotypes may bear relevant information regarding the distribution of the potential 8 273 tracemakers. They include: Dinosauromorpha tracks and tridactyl tracks (the latter may 274 correspond to poorly preserved chirotheriids or dinosauromorphs as well); and 275 indeterminate chirotheriid tracks, because in some localities these are not identified at 276 ichnogeneric level, but such ichnorecord indicates the presence of relatively large 277 archosaurs. Similarly, tetrapod swimming traces, even if they encompass different 278 producers (and include different ichnogenera; e.g., Xing et al., 2020), are also counted 279 as their presence is indicative of a peculiar locomotion gait, and thus provide 280 information on the palaeoenvironmental setting, and on the taphonomy of track bearing 281 localities. 282 Palaeoenvironmental settings of each locality/region are classified into four 283 major groups, from proximal to distal: 1) alluvial/inland (including fluvial and 284 lacustrine deposits), 2) distal alluvial/supratidal (including playa lake and coarse- 285 grained sabkha deposits), 3) coastal/tidal flats (including fine-grained sabkha or sabkha- 286 like deposits), and 4) shallow marine. The criteria to classify these settings follow the 287 palaeoenvironmental analyses of each work (see references in Table S1), including 288 specific palaeoenvironmental definitions and, especially in the absence of precise 289 information, the sedimentary characteristics of the facies preserving tetrapod traces. In 290 addition, in the case of palaeoenvironments defined as continental-marine transition 291 without further specification, we consider those composed of fine- to very fine-grained 292 and carbonate facies in the coastal group, whereas those composed of coarser facies are 293 put in the distal alluvial group. Regarding sabkha or sabkha-like settings, we follow a 294 similar rule: those with finer facies are in the coastal group, and those with coarser 295 facies are in the distal alluvial group. This responds to the fact that the coarser deposits 296 are considered as more proximal than the finer deposits. Notwithstanding, we might 297 expect further palaeoenvironmental interpretations of the track-bearing localities in 298 future works in order to refine these analyses. 299 300 3.1. Institutional abbreviations 301 302 IPS, Institut Català de Paleontologia Miquel Crusafont (formerly, Institut de 303 Paleontologia de Sabadell), Sabadell, Catalonia, Spain. 304 MGSB, Museu Geològic del Seminari de Barcelona, Barcelona, Catalonia, 305 Spain. 306 9 307 4. Results 308 309 4.1. Stratigraphy and sedimentology 310 311 The newly discovered tetrapod footprint localities of Penya Rubí, Puigventós 312 and Montmany, all from the middle Muschelkalk facies, are briefly described here. For 313 extended description and interpretation of each outcrop, see Text S1. Furthermore, our 314 results on the stratigraphy and sedimentology of those facies are compared with those 315 from Ortí et al. (2018) and references therein, along with those derived from the 316 tracksites described in Mujal et al. (2015, 2018a). Figure 2 summarizes the stratigraphic 317 position of the tracksites within the middle Muschelkalk succession. 318 The Penya Rubí outcrop (Fig. 3) includes a stratigraphic succession up to ~27 m 319 thick and encompasses the Lower Unit (Paüls Gypsum) and part of the Middle Unit 320 (Arbolí Gypsum and Guanta Sandstone). The succession presents a terrestrialization 321 trend (Fig. 3A). The lowermost part consists of whitish gypsum deposits overlying the 322 lower Muschelkalk carbonates. They correspond to the Paüls Gypsum. The overlying 323 deposits consist of alternating and finely laminated reddish mudstones and very fine- to 324 fine-grained sandstones. In between this reddish succession there is a distinct interval 325 (~50 cm thick) of finely laminated greyish mudstones and dolostones (Fig. 3A, B), 326 which laterally become coarsier and display cross lamination (Fig. 3C). The red layers 327 commonly display cross lamination (including unidirectional, wave and climbing 328 ripples) (Fig. 3D). Some intervals preserve abundant load and water escape structures 329 (Fig. 3E). All in all, these red deposits mostly show bidirectional water currents and 330 periods of rapid sedimentation. The surfaces of the greyish interval occasionally display 331 wrinkle structures (elephant skin-like textures; Fig. 3F), may indicating periods of low 332 energy environmental conditions. This part of the succession was mostly deposited 333 under subaqueous conditions and/or the substrate was mostly water saturated (high 334 moisture), though sporadic dryer episodes or seasons might also took place. We 335 interpret these deposits as most probably representing intertidal and sabkha-like areas, 336 where finely laminated microbial mats (Fig. 3B, G) were developed (greyish deposits 337 and dolostones), and correspond to the Arbolí Gypsum. Most of the tetrapod footprints 338 from Penya Rubí (i.e., those of relatively small size) are preserved on the surfaces of the 339 grey carbonate (dolostone) microbial mat deposits (lower arrow in Fig. 3A, and Fig. 3G, 340 H); yet the first reddish sandstones and mudstones also preserve sparse small-sized 10 341 tetrapod footprints, as well as a xiphosuran traceway (De Jaime-Soguero et al., 2020). 342 Notably, the large archosaur footprints are preserved at the basal surface of the mud- 343 cracked, medium-grained sandstone (upper arrow in Fig. 3A), representing the onset of 344 the Guanta Sandstone (see Text S1 and S3). Our interpretations match those by Calvet 345 and Marzo (1994), Mujal et al. (2018a) and Ortí et al. (2018), suggesting that during the 346 marine regression the Catalan Basin was a vast tidal flat, with a low relief that included 347 a mosaic of environments ranging from subtidal to supratidal areas (Ortí et al., 2017) 348 (see Text S1 for further details). The topmost part of the succession is built up of tabular 349 reddish medium-grained sandstones with cross stratification and red laminated 350 mudstones and fine-grained sandstones (Fig. 3A). This succession denotes a marked 351 palaeoenvironmental change towards a more terrestrial setting that represents the onset 352 of the Guanta Sandstone. Noteworthy, the succession of Pedrera de Can Sallent (see 353 Mujal et al., 2018a) can be generally compared to that of Penya Rubí, especially in 354 terms of granulometry, sedimentary structures, and strata arrangement: strata are finely 355 laminated, wave (bidirectional) ripples are common, and wrinkle structures most 356 probably induced by microbial activity are also present. Otherwise, the Pedrera de Can 357 Sallent succession differs with that of Penya Rubí in the main lithological composition: 358 the former is more siliciclastic than the latter. This difference may be explained by the 359 palaeogeographic position of the localities within the Catalan Basin (see Ortí et al., 360 2018; Texts S1 and S3). 361 The tectonization of the Puigventós outcrop (Fig. 4A) prevents the measuring of 362 a complete stratigraphic succession with confidence (though a composite section is 363 fairly possible; Fig. 2). The main lithological and sedimentological features reveal 364 closer similarities to the medium-grained sandstone at the top of the succession of 365 Penya Rubí (Guanta Sandstone; upper half in Fig. 3A) rather than to the underlying 366 fine-grained intervals (Arbolí Gypsum; lower half in Fig. 3A). The Puigventós 367 succession mostly consists of reddish fine- to medium-grained sandstones usually with 368 cross stratification and lamination that are interbedded with red mudstones. Wave 369 ripples are common, and occasional mud-cracked surfaces and moulds of hopper 370 crystals also occur. Bioturbation produced by invertebrates (consisting in both vertical 371 and horizontal burrows) is especially abundant in some sandstone layers. In general 372 terms, the succession is similar to that of Collcardús, previously reported by Mujal et al. 373 (2015), and located just 5 km eastwards. The Collcardús outcrops are composed of red 374 bed deposits corresponding to mudstones alternated with fine- to medium-grained 11 375 sandstones, often with cross stratification, ripples and, occasionally, desiccation cracks 376 (Mujal et al., 2015). Based on these features (see Text S1 for further details), we 377 interpret the palaeoenvironmental setting of Puigventós (and Collcardús) as a distal 378 alluvial area with frequent desiccation periods and with highly salty waters, but also 379 with flooding (at least periodical) events, which is consistent with the presence of 380 tetrapod swimming traces. The studied outcrop might correspond to the Guanta 381 Sandstone, although a short interval in the lowermost part could correspond to the 382 Arbolí Gypsum. In general terms, the Puigventós succession is here interpreted as a 383 proximal sabkha plain or a tidal mixed-flat (with notable terrestrial or terrigenous 384 influence, as denoted by a major presence of siliciclastic deposits), except for the 385 basalmost part, which it was probably more similar to the tidal flats of Penya Rubí. 386 The succession of Montmany (Fig. 4B–J) is similar to that of Puigventós and 387 Collcardús as well. The main components of the succession are decimetre-thick reddish 388 fine- to medium-grained sandstones, with cross stratification and lamination, 389 interbedded with red mudstones deposits ~0.5 to 1 m thick (Fig. 4B). Within sandstone 390 layers, wave ripples are common structures, but climbing and unidirectional flow 391 ripples are also present (Fig. 4C). Most of the tetrapod footprints are found on the basal 392 surfaces of the sandstone layers (Fig. 4D), tetrapod swimming traces (though not very 393 abundant) are also preserved. As in Puigventós, some sandstone layers are highly 394 bioturbated (Fig. 4E), with both vertical and horizontal sinuous burrows commonly with 395 meniscate infill. Other more occasional structures are wrinkled surfaces probably of 396 microbial mats (Fig. 4E), mud-cracks (Fig. 4G), moulds of large gypsum nodules (Fig. 397 4H) and of hopper crystals, all these being indicative of desiccation periods. Otherwise, 398 water escape and load structures (Fig. 4I) are also present, suggesting rapid flooding and 399 increase of the sedimentation rate and higher energy of the system. Of note, potential 400 xiphosuran traces have been identified in Montmany (IPS120436 and IPS120437), 401 further pointing to connections to the palaeocoast, though Triassic xiphosurid 402 ichnofossils are known from far inland settings in the nearby Pyrenean Basin (Mujal et 403 al., 2018b). These traces will be studied in future works and compared with the 404 xiphosuran traceway already described at the Penya Rubí locality (De Jaime-Soguero et 405 al., 2020). A distinct 25 cm thick massive carbonate layer (probably a dolostone) bears 406 Rhynchosauroides tirolicus Abel, 1926 footprints in concave epirelief, being different to 407 the rest of the succession (left in situ; arrow in Fig. 4J). According to all the mentioned 408 features, this succession may be equivalent to those of Puigventós and Collcardús, 12 409 mostly corresponding to the Guanta Sandstone. In this case, the facies correspond to a 410 distal alluvial setting, being a proximal sabkha plain, with salty waters and with 411 frequent desiccation periods, but also periods of flooding and a relatively strong 412 terrigenous inpunt. Nonetheless, as indicated by Ortí et al. (2018), some intervals (such 413 as the carbonate layer) may correspond to interdigitated parts of the Arbolí Gypsum 414 (Fig. 2C). 415 416 4.2. The middle Muschelkalk track record of the Catalan Basin 417 418 Numerous tetrapod tracks have been recovered from the Penya Rubí, Puigventós 419 and Montmany outcrops. They are assigned to at least 10 different ichnotaxa. 420 Specimens of the same ichnotaxon but from different localities may display distinct 421 features, though in some cases differences appear to be related to substrate composition, 422 as discussed below and in Text S3. In this section we briefly describe each tetrapod 423 ichnotaxon of the middle Muschelkalk ichnoassemblage from the Catalan Basin, mainly 424 from the three newly reportedlocalities (Penya Rubí, Puigventós and Montmany), but 425 also including remarks from the previously described localities of Collcardús (Mujal et 426 al., 2015) and Pedrera de Can Sallent (Mujal et al., 2018a). The detailed systematics of 427 each ichnotaxon, as well as additional figures are provided in the supplementary 428 information (Text S2, Figs. S1–S10). 429 Tracks of Procolophonichnium haarmuehlensis (Holst et al., 1970) have been 430 identified in the Penya Rubí locality by relatively small, pentadactyl and 431 semiplantigrade impressions (Figs. 5A, S1). The digit proportions and relative position 432 make their imprints wider than long. The digit imprints shape is moderately robust and 433 straight to distally curved outwards. The length of digit impressions increases from I to 434 III, with digit IV imprint slightly shorter than digit III. The imprint of digit I is the 435 shortest. The imprint of digit V is separated from the others and more proximally 436 positioned, and its length is subequal to digit II (Klein et al., 2015). Claw impressions 437 are preserved in all digits, being deeply impressed and markedly curved outwards. 438 Awaiting further analyses, including the study of relative depth patterns (e.g., Mujal et 439 al., 2020), procolophonid parareptiles and therapsid synapsids are considered the most 440 probable producers of P. haarmuehlensis (Klein et al., 2015; Marchetti et al., 2019c). 441 Three small-sized ichnites from Montmany have been referred to 442 Procolophonichnium isp. (Figs. 5B, S2). They are pentadactyl and plantigrade, with 13 443 robust and straight to slightly bent outwards digits imprints displaying relatively large 444 clawed tips. The lateral portion of the footprints is relatively deeply impressed, 445 suggesting a different trackmaker to those of P. haarmuehlensis. 446 Several footprints assigned to an indeterminate ichnospecies of Chelonipus 447 Rühle von Lilienstern, 1939 have been recovered from Puigventós and Montmany 448 localities (Figs. 5C, S2A, D, S3). As observed in the studied specimens, this ichnogenus 449 is characterised by a relatively wide trackway, with a low pace angulation (Haubold, 450 1971a; Lovelace and Lovelace, 2012; see Lichtig et al., 2018 for a review of the 451 ichnogenus). The footprints outlines are represented by roundish proximally concave 452 arches, with imprints of the digit tips usually displaying a dragging trail traces anteriorly 453 directed. The imprints are digitigrade to semiplantigrade and wider than long. The digit 454 impressions are short and with round tips. Pes tracks display three to five digits 455 impressions, while manus tracks show up to four digit impressions. A characteristic 456 feature is the impression of the interdigital area between digits II, III and IV. The 457 potential trackmaker of Chelonipus is traditionally referred to turtles (Lichtig et al., 458 2018). Nevertheless, other potential producers, such as temnospondyl amphibians (e.g., 459 Mujal and Schoch, 2020) or other unknown producers cannot be discarded. 460 The most abundant morphotype of the middle Muschelkalk is Rhynchosauroides 461 Maidwell, 1911 (Figs. 3G, H, 5D, E, F, S4, S5). This ichnotaxon is featured by 462 relatively small, lacertoid-like and markedly ectaxonic tracks, with slender digit 463 impressions. In both manus and pes tracks, the imprints of digits I to IV increase in 464 length and are curved inwards, while digit V imprint (similar to digit I in length) is 465 separated, more proximally positioned and rotated outwards. The manus impressions 466 tend to be semiplantigrade (occasionally digitigrade to semidigitigrade), with digit 467 imprints relatively shorter and wider than those of pes impressions. Pes tracks are 468 mainly digitigrade to semidigitigrade; most commonly only composed by the 469 impression of digits II, III and IV. Pes tracks anterolaterally or laterally overstep manus 470 tracks. All the footprints from Penya Rubí and Pedrera de Can Sallent (Mujal et al., 471 2018), most of those from Puigventós, and those from the carbonate layer of Montmany 472 (see Text S2 for details on the specimen numbers) fall into the range morphology of R. 473 tirolicus, which is well known from Middle Triassic coastal fine-grained and carbonate 474 deposits of the Italian Southern Alps (e.g., Avanzini and Renesto, 2002; Valdiserri and 475 Avanzini, 2007; Mietto et al., 2020), and possibly from Germany (e.g., Diedrich, 2002, 476 2008). Otherwise, the relatively poor preservation of other specimens from Montmany 14 477 and Puigventós (e.g., Figs. 5F, S5), as well as Collcardús (Mujal et al., 2015), precludes 478 an ichnospecific identification. The large chronological and palaeobiogeographical 479 occurrence of Rhynchosauroides may suggest that different taxa could have produced 480 these characteristic lacertoid-like tracks, most likely being small neodiapsids, including 481 lepidosauromorphs and/or archosauromorphs (e.g., Avanzini and Renesto, 2002; 482 Diedrich, 2002, 2008; Valentini et al., 2007; Mujal et al., 2018). 483 Tracks of Rotodactylus Peabody, 1948 have been recovered from Penya Rubí 484 and Puigventós localities (Figs. 5G, 6C, S6, S8). These footprints are digitigrade, longer 485 than wide, pentadactyl and relatively small. The digit length increases from I to IV. 486 Imprints of digits I to IV are straight, subparallel, with the tips markedly bent inwards. 487 Imprint of digit V is only represented with a round impression in a far proximal position 488 from the rest of the imprint, being a characteristic feature of this ichnogenus (Peabody, 489 1948; Haubold, 1971a; Klein and Lucas, 2010a; Niedźwiedzki et al., 2013). 490 Dinosauromorphs are considered the potential trackmakers of Rotodactylus (e.g., 491 Peabody, 1948; Haubold, 1967, 1999; Haubold and Klein, 2002; Brusatte et al., 2011; 492 Niedźwiedzki et al., 2013); non-dinosauromorph archosauromorphs have also been 493 proposed as producers (Padian, 2013), although a thorough track-trackmaker correlation 494 for this alternative attribution is not available so far. 495 The largest tetrapod ichnites recovered from the middle Muschelkalk of the 496 Catalan Basin belong to the ichnofamily Chirotheriidae. Two ichnospecies of 497 Chirotherium Kaup, 1835 have been recovered. Both morphotypes are characterised by 498 pes tracks with tightly grouped imprints of digits II, III, IV, being digit III the longest, 499 and with digit I imprint slightly separated and more proximally. Imprints of digits I to 500 IV are straight and distally tapering, with relatively large triangular claw impressions. 501 Digit V imprint is separated from the others, more proximally positioned and rotated 502 outwards. These are diagnostic features of Chirotherium, a very common morphotype 503 from Lower and Middle Triassic terrestrial deposits and with a global distribution 504 (Haubold, 1971a, 1984; Klein and Haubold, 2007; Klein and Lucas, 2010b; Díaz- 505 Martínez and Pérez-García, 2012; Lagnaoui et al., 2019; Xing and Klein, 2019). 506 From Montmany, two manus-pes sets of relatively small tracks with slender 507 (elongated) shape are conferred to Chirotherium sickleri Kaup, 1835 (Figs. 6A, S2A, 508 D). Pes tracks are semiplantigrade and manus tracks are semidigitigrade. In pes tracks, 509 digit II imprint is notably shorter than digit IV imprint. Manus tracks are smaller than 510 pes tracks, but with similar digit proportions and more anteriorly positioned. Pes tracks 15 511 are slightly outward rotated in comparison with the manus impressions, a feature 512 characteristic of this ichnospecies, and opposite to C. barthii (e.g., Klein and Lucas, 513 2010a; Klein et al., 2016). “Rauisuchian” (pseudosuchian) archosauriforms are possible 514 trackmakers of this ichnospecies (Klein and Lucas, 2010a). 515 The second ichnospecies recovered is Chirotherium barthii Kaup, 1835, found 516 in Puigventós and in the medium-grained sandstone stratum of Penya Rubí (upper arrow 517 in Fig. 3A, Figs. 6B, S7). Pes tracks are semiplantigrade and relatively large. The 518 diagnostic features of this ichnospecies (e.g., Haubold, 1971b, 2006; Klein and Lucas, 519 2010a) observed in the Catalan specimens are: the longest digit III impression, followed 520 by digit II and a clearly shorter digit IV imprint; the triangular, large claw impressions 521 of the pedal digits; the pedal digit V imprint outlining a large, deeply impressed oval- 522 shaped proximal pad, and thinning distally. Pseudosuchian archosaurs or stem 523 archosaurs are the potential trackmakers of this ichnospecies (Haubold, 2006; Haubold 524 and Klein, 2000, 2002; Klein and Haubold, 2003; Klein et al., 2011). 525 A single left pes track from Puigventós is referred to Isochirotherium Haubold, 526 1971a (Figs. 6C, S8). It is semiplantigrade and pentadactyl imprints, with robust digits 527 with rounded claw impressions. Imprints of digits I to IV are straight and subparallel, 528 wider on the middle-distal portion, being somewhat oval-shaped. The digit III imprint is 529 the longest, with the digit II imprint subequal in length. Imprint of digit IV is much 530 shorter, but longer than the impression of digit I imprint. These four digit imprints form 531 a compact group. The impression of digit V is separated from the others, proximally 532 positioned slightly curved outwards and a laterally orientated. Among Isochirotherium 533 ichnospecies, I. coureli (Demathieu, 1970) is the most similar to that from Puigventós 534 (e.g., Gand et al., 2007; Klein and Lucas, 2018). Despite the fact that the absence of the 535 typical large pad in the imprint of digit V (due to breakage of the slab) and the lack of 536 manus impressions make the ichnospecies identification uncertain, the Isochirotherium 537 tracks of Puigventós display the same features as that of Collcardús (see Mujal et al., 538 2015). In addition, one of the tracks recovered in Collcardús preserves a large pad 539 impression of the digit V, also characteristic of I. coureli. Thus, we assign all 540 Isochirotherium tracks of the middle Muschelkalk from the Catalan Basin to I. cf. 541 coureli. The potential trackmakers of Isochirotherium were archosaurs, as in 542 Chirotherium, though no skeletal counterparts are so far correlated to this ichnogenus 543 (Klein and Lucas, 2010a). 16 544 Several tracks recovered from Montmany and a single partial track from 545 Puigventós are attributed to Sphingopus ferox Demathieu, 1966 (Figs. 4C, D, 6D, S9). 546 The pes tracks are semiplantigrade with a characteristic functionally tridactyl trend, with 547 the predominating imprints of II, III and IV. The manus of this ichnogenus is located in 548 an inner position regarding the pes tracks. The diagnostic features of this ichnospecies 549 (e.g., Demathieu, 1966, 1985; Haubold and Klein, 2002; Gand et al., 2007; Klein and 550 Lucas, 2018) observed in the Catalan specimens are: the longest digit III imprint, 551 followed by a notably shorter digit II imprint, which is longer than digit IV imprint; the 552 relatively low angle of digits II and IV (27º–38º, mean of 31º); the impression of digit I 553 more proximally positioned respect to digits II–IV, located behind digit II imprint and 554 rotated outwards; the digit V imprint, being curved and rotated outwards, and more 555 proximally positioned than and clearly separated from the other digit imprints; the 556 smaller manus tracks positioned at the height of pedal digit III imprint and on the inner 557 side of pes tracks. This ichnotaxon has been related to dinosauromorph trackmakers 558 (Haubold and Klein, 2000; Haubold and Klein, 2002; Brusatte et al., 2011). 559 Moreover, several tracks from Puigventós and Montmany localities display 560 features characteristic of chirotheriid ichnotaxa (e.g., Demathieu and Demathieu, 2004; 561 Haubold and Klein, 2002) (Fig. S10). However, due to their poor and incomplete 562 preservation, and/or because they are isolated manus tracks (Fig. S10A), these ichnites 563 cannot be assigned to any ichnogenus. Of interest, some of these tracks were probably 564 impressed under swimming locomotion (Figs. S2D, S10B), a behaviour already known 565 from the Triassic archosaur ichnological record (e.g., Thomson and Droser, 2015; Mujal 566 et al., 2017a). 567 568 4.3. Distribution of the Middle Triassic track record: descriptive statistics 569 570 Table S1 consists in a database of the global Middle Triassic tetrapod track 571 occurrences, including up to 75 regions/areas/localities. On its basis, a counting study of 572 the presence/absence of the tetrapod ichnorecord in each region reveals a total of 329 573 tetrapod trace occurrences classified in 29 different morphotypes (mostly ichnogenera 574 but also other specific cases, see methods in section 3 above). Following the 575 palaeoenvironmental classification used in this work, 33% of the localities correspond 576 to inland settings, 32% to distal alluvial, 28% to coastal, and 7% to shallow marine (Fig. 577 S11). Noteworthy, a very few track occurrences are classified in the shallow marine 17 578 setting; therefore, the obtained results may suffer changes with future field data from 579 such settings. Despite the similar proportions of the three most represented 580 palaeoenvironments, the inland and distal alluvial settings accumulate, respectively, the 581 36.78% (121) and 34.35% (113) of all ichnological occurrences. The coastal settings 582 record the 25.84% (85) of the total occurrences, and shallow marine environments only 583 account for the 3.04% (10) of the total occurrences (Table S2). Also, the tetrapod 584 ichnodiversity recorded in distal alluvial (26 morphotypes) and inland (23 morphotypes) 585 settings is clearly higher than in those of the coastal (16 morphotypes) and shallow 586 marine (6 morphotypes) settings (Table S2). It should be noted that shallow marine 587 settings mainly yield swimming traces, which are not distinguished at a detailed 588 ichnotaxonomic level, though clearly different ichnogenera and ichnospecies are 589 included within swimming traces (for thorough descriptions of tetrapod swimming 590 ichnotaxa, see Xing et al., 2020, and references therein; see also Table S1). 591 Figure S12 shows that, among all the tetrapod trace occurrences analysed, the 592 dominant ichnogenera are: Rhynchosauroides (16.11%), Chirotherium (13.68%), 593 Isochirotherium (10.33%), Procolophonichnium (7.90%), Rotodactylus (7.29%), and 594 Synaptichnium (6.38%). Also, swimming traces morphotypes (4.56%) and 595 Chirotheriidae indet. tracks (4.26%) tend to be frequent in Middle Triassic outcrops. 596 The occurrence of the remaining tetrapod ichnogenera and morphotypes is relatively 597 low (each one representing <4% of the total occurrences) (represented within “Others” 598 in Fig. S12). Of note, the relative proportions of each ichnotaxon in each 599 palaeoenvironment (Fig. 7A) show the palaeoenvironmental distribution of each 600 tetrapod trace morphotype without considering the total number of footprints in each 601 region (i.e., counting only presence/absence of each morphotype in each region). 602 Therefore, these data reflect the tetrapod ichnodiversity, but not the relative abundance 603 of each ichnotaxa/morphotypes. 604 Figure 7B shows the total number of occurrences of each tetrapod 605 ichnotaxon/morphotype (see also Tables S2 and S3), Rhynchosauroides occurrences are 606 higher in coastal settings than in distal alluvial and alluvial settings. 607 Procolophonichnium shows the same trend with a proportionally higher presence in 608 coastal palaeoenvironments than in the other ones. The occurrences of Chirotherium 609 and Isochirotherium have a very similar trend to each other, being more abundant in 610 distal alluvial and inland palaeoenvironments, the opposite trend to those of 611 Rhynchosauroides and Procolophonichnium. The distribution of Synaptichnium 18 612 occurrences should be taken with caution, as some tracks assigned to 613 “Brachychirotherium” may correspond to the former ichnogenus (or to Chirotherium as 614 well; see discussion in Klein and Lucas, 2010b, 2018). The number of Chirotheriidae 615 indet. track occurrences is markedly higher in inland palaeoenvironments than in the 616 other ones (i.e., following the trend of the identified chirotheriid ichnogenera). Lastly, 617 occurrences referred to swimming traces show a relatively homogeneous distribution 618 through all palaeoenvironments. Table S3 shows the percentage of occurrence of each 619 morphotype in each palaeoenvironmental setting (taking into account the number of 620 localities from this palaeoenvironment). Rhynchosauroides and Procolophonichnium 621 have a markedly higher occurrence in coastal environments (90.5% and 57.1, 622 respectively) than in distal alluvial (66.7% and 29.2%, respectively) and alluvial (64.0% 623 and 24.0%, respectively) palaeoenvironments. This is, tracks of these two ichnogenera 624 are more frequently found in deposits corresponding to coastal settings than those of 625 distal alluvial and alluvial ones. As with the total number of occurrences, the 626 percentages of chirotheriid track occurrences are inverse to Rhynchosauroides and 627 Procolophonichnium, being higher in inland and distal alluvial palaeoenvironments than 628 in the coastal ones. Rotodactylus occurrences show a slight increase towards inland 629 settings, though it is not as marked as that of chirotheriid ichnotaxa. Therefore, Tables 630 S2 and S3 generally show the same proportions in number of occurrences and 631 percentage of occurrences for each ichnotaxon in each palaeoenvironments. 632 A comparison of the proportions of the different tetrapod morphotypes in each 633 palaeoenvironment (Fig. 7B) shows that Rhynchosauroides and Procolophonichnium 634 are proportionally more abundant in coastal settings than in distal alluvial and inland 635 palaeoenvironments. Such proportion decrease of these ichnogenera towards inland 636 settings is reverse to the tetrapod ichnodiversity (Table S2), which increases from 637 coastal to distal alluvial and inland settings (Fig. 8). Otherwise, the presence of 638 chirotheriid ichnotaxa (including Chirotherium, Isochirotherium and Chirotheriidae 639 indet.) and Rotodactylus increase in those palaeoenvironmental settings that have a 640 higher diversity. 641 Summarising, we can observe how the palaeoenvironmental distribution and 642 proportions of Rhynchosauroides and Procolophonichnium is generally inverse to that 643 of chirotheriids and to the track diversity (Figs. 7B, 8). This is especially well-reflected 644 by the tetrapod ichnoassociations of the Middle Triassic Western Tethys, which 645 represent the bulk of data of the analysed localities (Table S1). 19 646 647 5. Discussion 648 649 5.1. Palaeoecology of the middle Muschelkalk tetrapod ichnoassociations 650 651 In the Catalan Basin, the onset of the detrital siliciclastic middle Muschelkalk 652 deposits over the marine carbonate succession of the lower Muschelkalk mirrors a 653 regression of the Tethys during the late Anisian–early Ladinian. Areas such as 654 Puigventós and Montmany (Fig. 4) record a succession of changing/alternating 655 environmental settings, ranging from relatively low energy conditions and evaporation 656 periods (i.e., during the development of hopper crystals, gypsum nodules and 657 desiccation cracks) to floodings and events of increased energy with water currents 658 (medium- to coarse-grained thick bedded sandstones with cross stratification; as well as 659 the presence of abundant vertical invertebrate burrows, and horizontal sinuous burrows 660 as well). In the palaeoenvironments of the Puigventós and Montmany successions, 661 relatively large archosaur tracks are found (Chirotherium, Isochirotherium and 662 Sphingopus ichnogenera, as well as indeterminate chirotheriid tracks), even if extensive 663 surfaces are not exposed. This most probably indicates that their trackmakers were 664 common inhabitants of these environments. In contrast, the relatively low presence of 665 Rhynchosauroides indicates that their trackmakers (generally small-sized diapsid 666 reptiles) were much less abundant and/or that the preservation of their more gracile 667 footprints was difficult. Even if taphonomic and sampling biases exist, they alone 668 cannot explain the low proportion of Rhynchosauroides footprints in these settings 669 (being much less abundant than the chirotheriid tracks; Figs. 7, 8, Text S2), especially if 670 tracks of this ichnogenus dominate in nearby localities (i.e., Penya Rubí and Pedrera de 671 Can Sallent). In this regard, the preservation of skin and claw impressions in the 672 Chirotherium barthii specimen IPS85803 indicates that the substrate was able to record 673 small and delicate details and structures, which could include small-sized tetrapod 674 footprints. These observations support the hypothesis that environmental conditions 675 constrained the spatial or areal distribution of tetrapods. Furthermore, Rotodactylus 676 tracks (with sizes similar to those of Rhynchosauroides) are more abundant in 677 Puigventós than in Penya Rubí, denoting a similar distribution to that of chirotheriid 678 tracks. This is, even if Rotodactylus specimens are of small size, they are more abundant 679 in deposits that appear not to favour their preservation. Therefore, the low presence of 20 680 Rhynchosauroides is probably not caused by a low potential of preservation of small- 681 sized footprints, but by an actual low presence of their trackmakers. Moreover, some of 682 the Puigventós slabs containing Rhynchosauroides (e.g., IPS110267 and IPS110269) 683 display thin laminae, similar to the microbial mats of Penya Rubí (see below). In the 684 same way, the tracks of Rhynchosauroides tirolicus from the Montmany locality are 685 only found in a distinct carbonate layer (interbedded within a red bed succession of 686 mudstones and sandstones; Fig. 4J), where no other ichnotaxa have been observed. This 687 could also denote a palaeoecology-related distribution of this ichnogenus, since it is 688 more common within certain lithologies of various settings that are different from those 689 characterising the Puigventós and Montmany successions. In a qualitative approach, 690 these observations on the presence/absence and relative abundance of ichnotaxa agree 691 with the expected results applying the census methods of Marchetti et al. (2017): poorly 692 exposed surfaces of the Puigventós and Montmany successions (Fig. 4A, B, D), as well 693 as the sandstone layer from the upper portion of the Penya Rubí succession (upper 694 arrow in Fig. 3A), (usually) only preserve relatively large (archosaur) footprints, 695 whereas the carbonate layers of the lower portion of the Penya Rubí succession (lower 696 arrow in Fig. 3A; see below) preserve only small-sized ichnotaxa (dominated by 697 Rhynchosauroides tirolicus). These distinct distributions are also found in the 698 previously described middle Muschelkalk localities from the Catalan Basin: the surface 699 of Collcardús (Mujal et al., 2015) contains seven footprints of chirotheriids and one of 700 Rhynchosauroides, whereas on the surfaces of Pedrera de Can Sallent (Mujal et al., 701 2018a) all footprints are of Rhynchosauroides (R. tirolicus, according to the reanalysis 702 of the present work; see Text S2), except of a single and poorly preserved indeterminate 703 footprint of a relatively large size. 704 In contrast to Puigventós, Montmany and Collcardús, the very fine-grained and 705 carbonate finely-laminated deposits of the Penya Rubí locality presents extremely 706 abundant Rhynchosauroides tirolicus footprints (Fig. 3G, H), whereas chirotheriid 707 tracks are absent in the very same layers. Procolophonichnium and Rotodactylus are 708 present, although these track morphotypes are much less abundant. The presence of 709 microbial mats in the sedimentary succession of Penya Rubí might have prompted the 710 high-quality preservation of the ichnites, including the preservation of scale prints, even 711 if the trackmakers of Rhynchosauroides and Procolophonichnium were lightweight 712 organisms. In fact, in present day intertidal areas with growing of microbial mats, 713 Carmona et al. (2011) correlated the preservation of tiny details of footprints (in their 21 714 case, skin of birds’ feet) with the presence of thin microbial mats. Such good quality of 715 preservation in microbial mats may depend on the specific environmental conditions, 716 water content and mat overgrowth, affecting the rheological properties of the substrate 717 (Marty et al., 2009; Marchetti et al., 2019b). We therefore suggest that the Penya Rubí 718 fossil footprints underwent similar formation and preservation processes (microbial 719 mats are also finely laminated), within a similar environment, as that reported by 720 Carmona et al. (2011). A similar high-quality preservation of tetrapod tracks is found in 721 the Anisian successions of Winterswijk, the Netherlands (Demathieu and Oosterink, 722 1983, 1988; Marchetti et al., 2019c) and Southern Alps, Italy (Avanzini, 2000; Mietto et 723 al., 2020). Similar experimental analyses on the preservation of footprints on microbial 724 mats carried out by Marty et al. (2009) could also explain the virtually absence of large 725 ichnotaxa: their trackmakers would have moved with difficulties on such substrates, 726 being too inconsistent to support the weight of large organisms. 727 From the Rhynchosauroides-dominated tracksite of Pedrera de Can Sallent, 728 Mujal et al. (2018a) documented three different types of footprint preservation 729 correlated to the substrate rheology and environmental variations. In this regard, most 730 samples of the Rhynchosauroides from Penya Rubí would be a mix between 731 preservation type 2 (high number of footprints) and preservation type 3 (high level 732 definition in a small sampling) of Mujal et al. (2018a). The high quality of most 733 footprints would be enhanced by the presence of microbial mats (e.g., Marty et al., 734 2009; Carmona et al., 2011; Marchetti et al., 2019b). The high abundance of footprints, 735 moreover, may have resulted from a combination of: (1) increased activity of the 736 trackmakers (i.e., environment favourable for their presence), implying that the 737 trackmakers would be gregarious as suggested by Demathieu and Demathieu (2004) 738 (see also Diedrich, 2008; Mujal et al., 2016b, 2018a); (2) high preservation potential 739 because of the presence of microbial mats, implying a potential overrepresentation of 740 trackmakers in cohesive substrates exposed during a relatively long period (i.e., time 741 averaging of substrates, see Falkingham, 2014). An additional explanation for the 742 abundance of Rhynchosauroides is that this ichnogenus was probably produced by 743 several different small- to medium-sized “lacertoid-like” taxa (neodiapsids, including 744 archosauromorphs and lepidosauromorphs), which would have been common 745 inhabitants of the Middle Triassic coastal settings (cf. Ezcurra, 2016). In this sense, the 746 high presence of Rhynchosauroides might be a reflection of an expansion of reptiles that 747 printed similar ichnites and adapted to coastal areas and/or continental floodplains (Fig. 22 748 8). Even if coastal settings were more favourable to the presence of Rhynchosauroides 749 trackmakers, they were also present in alluvial settings (Fig. 7, Table S1; see also 750 discussion above). This indicates that trackmakers were adapted to a wide range of 751 environments and/or that Rhynchosauroides encompass a wide range of trackmakers. 752 The latter is also supported by the fact that the time span of this ichnogenus is very 753 long, from the late Permian to the Late Jurassic (Valentini et al., 2007; Avanzini et al., 754 2010; Lucas, 2019; Marchetti et al., 2019d; Schneider et al., 2020). As noted in section 755 4.2 above and Text S2, the Rhynchosauroides tracks on IPS110265 from Puigventós are 756 different from the other specimens from the same locality and from those of the nearby 757 Penya Rubí and Pedrera de Can Sallent localities. This could be related to the presence 758 of a different trackmaker, being the trackmakers of the imprints on IPS110265 from a 759 more inland setting than the others. 760 Other tetrapod ichnotaxa, not as abundant as those previously discussed, also 761 appear to be linked to specific palaeoenvironments (Table S1). Procolophonichnium 762 haarmuehlensis tracks are only found, together with Rhynchosauroides, in the microbial 763 mat layers of Penya Rubí. This ichnospecies is more commonly found in coastal or 764 marine-influenced palaeoenvironments, although it is also present in terrestrial or more 765 inland settings, such as those from Spain, Germany and Morocco (see Klein et al., 766 2015). In addition, the Chelonipus specimens from the Puigventós locality represent the 767 first Middle Triassic record of the ichnogenus outside Germany, where it is present 768 within coastal settings (Lichtig et al., 2018). Chelonipus is also known from older 769 terrestrial Triassic localities from the USA (Lovelace and Lovelace, 2012), as well as 770 from coastal ichnosites of the Upper Triassic of Spain (Reolid et al., 2018) and 771 Germany (Lichtig et al., 2018). Rotodactylus, although present in both fully terrestrial 772 and coastal-influenced palaeoenvironments, is more abundant in the terrestrial ones (see 773 further discussion in section 5.2 below). 774 An interesting occurrence is that of potential dinosauriforms (Sphingopus ferox) 775 in the Montmany and Puigventós successions. These footprints further support former 776 studies and inferences that this group was already present during the Middle Triassic, as 777 also suggest the occurrences of Sphingopus from France (see Gand et al., 2007), 778 Germany (Haubold and Klein, 2000, 2002; Klein and Lucas, 2018) and Poland 779 (Brusatte et al. (2011). Further material may help to elucidate the palaeoenvironmental 780 distribution and general evolution of the group, as well as the nature of the potential 781 trackmakers. 23 782 To sum up, the different middle Muschelkalk localities here surveyed and 783 reviewed suggest that the Rhynchosauroides-dominated ichnoassociations were 784 generally linked to low energy environments with more marine influence, such as 785 intertidal flats, as well as distal sabkha plains (see also Mujal et al., 2018a). As already 786 suggested (Diedrich, 2002, 2008; Mujal et al., 2018a), a separate ichnocoenosis for 787 Rhynchosauroides may characterise the Middle Triassic coastal settings. On the 788 contrary, the Chirotheriidae-bearing ichnoassociations likely correspond to more 789 terrestrial environments (although still with marine influence), such as alluvial plains 790 and inland sabkha settings (Fig. 13). Of note, the two ichnoassociations of Penya Rubí 791 (lower and upper) mirror the change from the Arbolí Gypsum to the Guanta Sandstone, 792 representing the onset of a more terrestrial environment (see Text S3 for further 793 discussion and details) and thus prompting the appearance of chirotheriid tracks. 794 795 5.2. Middle Triassic tetrapod palaeoecology and palaeobiogeography of the Western 796 Tethys 797 798 The palaeoenvironmental distribution of tetrapod ichnotaxa within the middle 799 Muschelkalk of the Catalan Basin mirrors the palaeobiogeographic distribution at 800 Western Tethys scale. As shown below, the detailed analysis of the occurrence and 801 absence of tetrapod ichnotaxa (Figs. 7, S11, S12, Tables S2, S3) demonstrates that 802 tetrapod ichnofacies can be a useful tool contributing to the understanding of past 803 ecosystems and their evolution (Hunt and Lucas, 2007a, 2007b). 804 Our database of the Middle Triassic tetrapod ichnotaxa and localities all over the 805 world, including the specific time interval and palaeoenvironmental settings (Table S1), 806 shows that the distribution of ichnotaxa appears to be linked to the environmental 807 changes derived from different marine transgressions (Fig. 7) (as reflected in the middle 808 Muschelkalk from the Catalan Basin), being especially notable in the Western Tethys 809 domain (cf. Diedrich, 2002, 2008, 2015; Mujal et al., 2018a). It is important to remark 810 that most of the Middle Triassic tetrapod footprint localities so far known are dated as 811 Anisian, and only a few of them correspond to the Ladinian (Fig. 1; see Table S1 for 812 references). This could be related to the fact that during most part of the Ladinian most 813 of these Triassic basins were under marine settings (e.g., Escudero-Mozo et al., 2015; 814 Franz et al., 2015; Manzanares et al., 2020; and references therein) (Fig. 1). In this 815 sense, successions ranging from the Anisian to the Ladinian, as those from the middle 24 816 Muschelkalk, give clues to the understanding of the (ichno-) faunal evolution during the 817 Middle Triassic. 818 During the latest Early Triassic (Olenekian) and the early steps of the Middle 819 Triassic (Anisian), the Western Tethys basins were characterised by the presence of 820 archosauromorphs (Mujal et al., 2016b, 2017a). Chirotheriid tracks (and especially 821 Chirotherium barthii) and Rhynchosauroides are abundant in Spain, France, Morocco, 822 Italy, Switzerland, Germany, Poland, United Kingdom and the USA (see Table S1 for 823 references). Other ichnotaxa are also recorded but not as widely present and abundant as 824 the previous ones (e.g., Procolophonichnium, Chelonipus, Isochirotherium, 825 Synaptichnium, and Rotodactylus, though the latter may be occasionally abundant). 826 Interestingly, Chirotherium barthii and Rhynchosauroides are present in further Middle 827 Triassic localities from China (Xing et al., 2013; Xing and Klein, 2019). C. barthii is 828 also known from Argentina (Lagnaoui et al., 2019), indicating a virtual global 829 distribution of the corresponding trackmakers. 830 Large-sized tracks referred to chirotheriids are also recorded in some 831 southwestern-southern Gondwanan regions (e.g., Argentina: Marsicano et al., 2004; 832 Melchor and de Valais, 2006; Lagnaoui et al., 2019; Brazil: Leonardi, 1980), including 833 Chirotherium and Isochirotheirum. Therefore, the group of relatively large chirotheriid- 834 trackmakers had already a cosmopolitan distribution during the early stages of the 835 Triassic, as recently shown in the review of the Early Triassic tetrapod fauna by 836 Romano et al. (2020). This is also indicated by the widespread presence across central 837 Pangaea of Protochirotherium tracks in the Lower Triassic (Fichter and Kunz, 2004; 838 Klein and Niedźwiedzki, 2012; Klein et al., 2013), which possibly extends back to the 839 upper Permian (Bernardi et al., 2015; Marchetti et al., 2019d). Rotodactylus tracks are 840 slightly more abundant in terrestrial palaeoenvironments than in coastal ones (Fig. 7B), 841 which possibly reflect a similar distribution to that of chirotheriid tracks. In fact, 842 chirotheriid and Rotodactylus ichnotaxa are commonly found associated (Table S1). 843 Palaeoenvironmental and/or taphonomic biases exist as demonstrated by the 844 poor (or null) ichnological record of non-amniote tetrapods (temnospondyls sensu lato) 845 in the Western Tethys during the Anisian. Only dubious records from few localities of 846 France and Germany are known (Haubold, 1971a; Demathieu and Durand, 1991; Gand 847 et al. 2007). Out from the Western Tethys, potential amphibian tracks are known only 848 from the Moenkopi Formation, USA (Klein and Lucas, 2010a), and New South Wales, 849 Australia (Farman and Bell, 2020) (Table S1). This is in contrast with the important 25 850 osteological record of Anisian temnospondyls from the Western Tethys (e.g., Spain, 851 Fortuny et al. 2011b; France, Germany and Poland, Schoch and Milner 2000). More 852 recently, Mujal and Schoch (2020) reported temnospondyl tracks from the Ladinian 853 (Lower Keuper) of southern Germany. These authors hypothesised that the lack of 854 record is most probably related to the ecological preferences of temnospondyls, which 855 usually roamed subaquatic settings performing a buoyant/swimming locomotion, hence 856 reducing the preservation potential of footprints. 857 Even if transgressions resulted in different environments across the Western 858 Tethys, basins remained connected during the Middle Triassic as demonstrated by the 859 relatively homogeneous tetrapod ichnoassemblages throughout this domain. With the 860 development of coastal areas, the trackmakers of Rhynchosauroides took advantage as 861 reflected by the dominance of this ichnogenus in the Western Tethys coastal 862 palaeoenvironments (Diedrich, 2008; Mujal et al., 2018a). Interestingly, 863 Procolophonichnium tracks have a similar palaeoenvironmental distribution to that of 864 Rhynchosauroides (Fig. 7), confirming the previous observations of Diedrich (2002) for 865 the Central European Basin. Noteworthy, Rhynchosauroides is already abundant in the 866 marginal marine setting of the Arenaria de Val Gardena Formation, from the Lopingian 867 of Italy (Valentini et al., 2007; Marchetti et al., 2019d). This could be indicative of a 868 similar palaeoecology of this older Rhynchosauroides morphotype to those of the 869 Middle Triassic; hence further investigations should focus on the comparison of the 870 whole record of this ichnogenus. 871 Rhynchosauroides already had a global distribution by the Early and earliest 872 Middle Triassic, being recorded in western and central Europe (Haubold, 1971a, 1971b; 873 Demathieu, 1985; Diedrich, 2002, 2008; Demathieu and Demathieu, 2004; Klein and 874 Niedźwiedzki, 2012; Mujal et al., 2016b, 2017a), western USA (Klein and Lucas, 875 2010a; Lovelace and Lovelace, 2012), Argentina (Melchor and de Valais, 2006) and 876 China (Xing and Klein, 2019). This ichnogenus encompasses a high number of 877 ichnospecies, many of them possibly described from specimens with 878 extramorphological variations (cf. Klein and Niedźwiedzki, 2012); similarly, in several 879 cases Rhynchosauroides tracks are usually not identified at the ichnospecies level 880 (Table S1). As a result, this ichnogenus is in need of a comprehensive revision in order 881 to determine its ichnospecific diversity. In any case, certain Rhynchosauroides 882 morphotypes are characteristic of specific time intervals and palaeoenvironmental 883 settings: R. schochardti, known from the Lower and lowermost Middle Triassic 26 884 terrestrial settings, and R. tirolicus and R. peabodyi, known from the Middle Triassic 885 coastal settings of the Western Tethys (Table S1). Therefore, the global distribution of 886 Rhynchosauroides during the Early Triassic could be explained by the presence of 887 trackmakers mostly adapted to terrestrial environments. Several of these 888 palaeoenvironments would have evolved to coastal settings during the Middle Triassic, 889 possibly prompting a turnover within the trackmakers of Rhynchosauroides. The new 890 trackmakers might have diversified and became dominant due to the expansion of 891 coastal settings. Therefore, there could have been a turnover of faunas from the Early to 892 the Middle Triassic, especially in the Western Tethys, due to the expansion of coastal 893 settings and in detriment of most large archosaurians (see below). Nonetheless, a 894 research bias, with the coastal settings from the Lower Triassic less studied than those 895 of the Middle Triassic, cannot be ruled out. 896 Additionally, tetrapod swimming trace fossils, even if not abundant, are present 897 in all the palaeoenvironments of the Middle Triassic (Fig. 7, Table S1). This could point 898 to a potential taphonomic bias towards the preservation of footprints in environments 899 with a relatively recurrent presence of water. Therefore, such bias could also be applied 900 at a greater scale; this is, there could be a preferential preservation of coastal deposits 901 against more inland ones, and thus the likelihood of finding tetrapod footprints is 902 greater in coastal settings. However, as shown in section 4.3 above, tetrapod track 903 localities of coastal settings are approximately the same as those of alluvial 904 palaeoenvironments (Fig. S11). Regarding the shallow marine settings, a potential 905 research bias is observed, as track localities under this palaeoenvironment are markedly 906 less represented than the other ones (Fig. S11). 907 The potential faunal turnover within the trackmakers of Rhynchosauroides can 908 be further explored by analysing the osteological record. Ezcurra and Butler (2015, 909 2018) and Foth et al. (2016) already documented an increase of the morphological 910 disparity of archosauromorphs during the late Early and early Middle Triassic, although 911 the low sampling of Lower Triassic deposits should also be considered (see also Butler 912 et al., 2011; Romano et al., 2020). Ezcurra and Butler (2018), as well as Irmis and 913 Whiteside (2012), suggested that the low rates of diversification within 914 archosauromorphs, but also generally within tetrapods, could be linked to perturbations 915 of the global carbon cycle in the aftermath of the end-Permian mass extinction (for 916 alternative interpretations on the magnitude of the extinction, see Lucas, 2017). The 917 stabilization of the carbon cycle, together with the expansion of coastal settings, would 27 918 have allowed the diversification of certain tetrapod groups. Interestingly, MacDougall et 919 al. (2019) also documented a turnover within parareptiles during the early steps of the 920 Triassic (see Ruta et al., 2011), showing also a sharp decline during the Middle Triassic; 921 these changes could be linked to the radiation of archosauromorphs. In this sense, the 922 Lower and Middle Triassic tetrapod localities are commonly dominated by 923 archosauromorph faunas (e.g., Pinheiro et al., 2016) and lepidosauromorphs, though the 924 latter being less abundant (e.g., Schoch and Sues, 2018; Simões et al., 2018; Cavvichini 925 et al., 2020; Sobral et al., 2020). Interestingly, the tetrapod tracks apparently mirror such 926 changes, with a high increase and dominance of footprints produced by 927 archosauromorphs (e.g., Mujal et al., 2017a). 928 As observed between the middle Muschelkalk localities of the Catalan Basin, 929 while in Penya Rubí and Pedrera de Can Sallent small-sized footprints are extremely 930 abundant and large ichnotaxa (i.e., chirotheriids) are completely absent, in Puigventós, 931 Montmany and Collcardús chirotheriids are proportionally much more abundant than 932 small-sized taxa (e.g., Rhynchosauroides). Interestingly, Penya Rubí and Pedrera de 933 Can Sallent correspond to tidal flat settings, mostly composed of carbonate and very 934 fine- to fine-grained siliciclastic deposits, whereas Puigventós, Montmany and 935 Collcardús correspond to distal alluvial and proximal sabkha settings, mostly composed 936 of fine- to medium-grained siliciclastic deposits. In addition, small ichnotaxa (i.e., 937 Rhynchosauroides among others) are much less abundant than in the tidal (coastal 938 deposits), even if present in these distal alluvial settings (Figs. 7B, 8). The main 939 difference between Penya Rubí and Puigventós and Montmany is the 940 palaeoenvironmental setting, with more terrestrial influence in Puigventós and 941 Montmany than in Penya Rubí (Texts S1 and S3). These considerations can be 942 discussed at Western Tethys (and possibly Pangaean) level: as recently discussed for the 943 Upper Triassic boreal successions (Klausen et al., 2020), the proliferation of coastal 944 areas, with more marine influence due to the Tethys transgression, may led to the loss of 945 habitats of large archosaur faunas (mostly represented by chirotheriids in the 946 ichnological record). As reflected in the Western Tethys (Table S1), large archosaur 947 ichnofaunas in palaeoenvironments with relatively strong marine influence are 948 persistent and diverse (Fig. 7), though in absolute numbers (e.g., Diedrich, 2008, 2015; 949 Mujal et al., 2018a; Marchetti et al., 2020; Mietto et al., 2020) they are notably less 950 abundant than in terrestrial (alluvial) settings (Figs. 7, 8, Tables S2, S3). This may be 951 further indicative of environmental constraints for large-sized archosaurs as discussed in 28 952 section 5.1 above. Nonetheless, further quantitative analyses are necessary to untangle 953 the distribution of chirotheriid ichnotaxa. 954 The distribution of Middle Triassic tetrapod ichnotaxa also shows that the distal 955 alluvial and inland settings present a higher (ichno-) diversity than the coastal settings 956 (Figs. 7B, 8, Tables S2, S3). This could respond to the harsher conditions on coastal 957 settings respect to more terrestrial ones. As a result, this could have favoured the 958 proliferation of more generalist taxa (like the potential producers of Rhynchosauroides; 959 e.g., Demathieu and Demathieu, 2004; Petti et al., 2013; Mujal et al., 2016b) that better 960 adapted to these environments. In this regard, even without counting the absolute 961 number of footprints of each locality, a reduced tetrapod ichnodiversity is observed in 962 coastal settings, where Rhynchosauroides and Procolophonichnium tracks dominate 963 (Diedrich, 2008; Mujal et al., 2018a; Marchetti et al., 2020; Mietto et al., 2020). In the 964 same way, as suggested by Marchetti et al. (2020), the proportionally higher number of 965 relatively large archosaur tracks in alluvial settings is probably linked to a different 966 palaeoecology of the trackmakers. 967 We observe that, in fairly age equivalent localities, differences in ichnofaunal 968 composition exist (Fig. 7, Tables S1, S2, S3). Therefore, at the Middle Triassic scale, 969 the presence of certain ichnotaxa is generally more linked to the environmental setting 970 than to the specific age of the deposits. Thus, the temporal evolution of 971 palaeoenvironments may show an (ichno-) faunal replacement, as observed in the Upper 972 Triassic (Stubbs et al., 2013; Bernardi et al., 2018). Further, such environmental 973 constraint would eventually trigger the proliferation of faunas more adapted to the new 974 environments, such as the dinosaur ascendants, which may be poorly represented in the 975 track record before the Ladinian in the Western Tethys (Table S1). In this regard, 976 thorough revisions of ichnotaxa attributed to dinosauromorphs, such as Rotodactylus 977 and Sphingopus (see Peabody, 1948; Haubold, 1999; Haubold and Klein, 2000, 2002; 978 Brusatte et al., 2011; and Padian, 2013 for alternative interpretations), together with the 979 (so far poor) osteological record, are necessary to provide a wider picture of the 980 temporal rage and spatial distribution of the dinosaur lineage. The decline of non- 981 dinosauromorph archosaurs, leading to the dominance of the dinosaur lineage has been 982 recently discussed for the Upper Triassic tetrapod record on the basis of (1) 983 morphological and biomechanical disparity (Stubbs et al., 2013) and (2) the archosaur 984 to dinosaur footprint turnover linked to the Carnian Pluvial Event (Bernardi et al., 985 2018). During the Middle Triassic, dinosauromorphs were still marginal components of 29 986 tetrapod ecosystems, becoming significantly more abundant by the end of the Middle 987 Triassic and especially during the Late Triassic. All these observations highlight the 988 necessity of carrying out facies analyses together with ichnological (and generally 989 palaeontological) studies. This is necessary to explore the role that the Middle Triassic 990 environmental changes (linked to marine transgressions) played on the shape of tetrapod 991 ecosystems, including also the radiation of the dinosaur lineage. The expansion of 992 coastal and/or marine influenced environments possibly prompted a regression/decrease 993 of large archosaur faunas (potential producers of chirotheriids), which later evolved to 994 new faunas that took advantage of the new environmental settings (e.g., as represented 995 by the evolutionary novelties present in dinosauromorphs and descendants). It is 996 important to note that, in any case, small-sized neodiapsid faunas (mostly represented 997 by Rhynchosauroides) persisted (and expanded) in these coastal/marine influenced 998 environments (Diedrich, 2008; Mujal et al., 2018a, and references therein), though they 999 almost disappeared in the Late Triassic. 1000 In summary, we here suggest a link between the Middle Triassic environmental 1001 changes and the presence and relative abundance of certain (ichno-) faunas (Fig. 13). In 1002 this way, our data permit to distinguish between palaeo(bio)geographic domains of the 1003 Western Tethys: marine influenced ichnoassociations (Rhynchosauroides-dominated) 1004 and terrestrial ones (non-Rhynchosauroides-dominated). Moreover, in a reverse 1005 analysis, (i) the identification of palaeoenvironments (especially those yielding 1006 Rhynchosauroides and Chirotheriidae tracks) and (ii) the age of the successions (i.e., 1007 Lower or Middle Triassic) might allow to differentiate the potential producers of these 1008 ichnotaxa. 1009 1010 6. Conclusions 1011 1012 The Middle Triassic terrestrial record represents an excellent case to study the 1013 tetrapod palaeoecology. This is especially the case of the tetrapod ichnological record, 1014 particularly abundant from this time interval, as ichnites are preserved in the actual 1015 habitats of the corresponding trackmakers. Among the different track localities globally 1016 known (Table S1), those from the middle Muschelkalk successions of the Catalan Basin 1017 are of particular interest. The tracks herein reported, together with those previously 1018 known, reveal a relatively rich ichnodiversity, including: Procolophonichnium 1019 haarmuehlensis, Procolophonichnium isp., Chelonipus isp., Rhynchosauroides tirolicus, 30 1020 Rhynchosauroides isp., Rotodactylus isp., Chirotherium cf. sickleri, Chirotherium 1021 barthii, Isochirotherium cf. coureli, Sphingopus ferox, and Chirotheriidae indet. Such 1022 ichnotaxa are widely known among the Western Tethys basins and some 1023 (Rhynchosauroides and C. barthii) even have a global distribution. 1024 The correlation of each ichnotaxon to its palaeoenvironmental setting, together 1025 with the comparison with further localities, shows that environmental changes (linked to 1026 the Middle Triassic marine transgressions) constrained the distribution of tetrapod 1027 faunas. In the Catalan Basin, the aforementioned ichnotaxa are settled in well- 1028 differentiated ichnoassociations, which are linked to different palaeoenvironments. This 1029 is, tetrapod ichnotaxa are probably controlled by the presence of specific facies. 1030 The most representative ichnotaxon reflecting such constraints is 1031 Rhynchosauroides: in coastal palaeoenvironments it is commonly the dominant 1032 ichnotaxon (suggestive of a distinct ichnocoenosis: Diedrich, 2008; Mujal et al., 2018a), 1033 whereas in more inland settings its presence is reduced. Similarly, Procolophonichnium 1034 tracks are also more abundant in coastal settings than in alluvial ones. Chirotheriid 1035 footprints show the opposite trend: they are scarce in coastal settings, especially those 1036 built up of fine-grained facies, and commonly dominate in more terrestrial settings. 1037 Therefore, Middle Triassic ichnoassociations are generally either Rhynchosauroides- 1038 dominated (coastal settings, especially those with fine-grained facies) or non- 1039 Rhynchosauroides-dominated (alluvial settings, even with some marine influence, and 1040 with an increased presence of chirotheriid tracks). Furthermore, tetrapod track diversity 1041 in alluvial settings is notably higher than in coastal settings, suggesting that the 1042 trackmakers of Rhynchosauroides, possibly being generalist organisms, took advantage 1043 in coastal palaeoenvironments. This could possibly mirror faunal turnovers during the 1044 Early and Middle Triassic recovery of the ecosystems. 1045 This work highlights the importance of facies analyses when studying tetrapod 1046 ichnofossils. This may result in a better understanding on the presence/absence of 1047 specific ichnotaxa. An integrated sedimentological and ichnological approach sheds 1048 light on the tetrapod palaeobiogeography at the given time interval. In this regard, the 1049 palaeoenvironmental constraints evidenced by the middle Muschelkalk of the Catalan 1050 Basin show the palaeobiogeographic variation of tetrapods of the whole Middle Triassic 1051 Western Tethys, and thus contribute to the understanding of the (ichno-) faunal 1052 responses to environmental change. 1053 31 1054 Acknowledgments 1055 Our special thanks to Belén Muñoz for reporting the discovery of the Puigventós 1056 ichnosite, as well as to Joan Soler for guidance to the outcrops. Manel Méndez, Marc 1057 Riccetto, Alejandro Granados, Montse Vilalta and Albert Vidal are acknowledged for 1058 their fieldwork support and Xènia Aymerich (ICP) for the preparation of the track 1059 samples. We acknowledge Jordi Ibáñez-Insa (GEO3BCN-CSIC, Barcelona) for 1060 mineralogical determinations. C.D.J.S. is granted by a FI AGAUR fellowship (ref. 2020 1061 FI_B 00472) funded by the Secretaria d’Universitats i Recerca de la Generalitat de 1062 Catalunya and the European Social Fund. E.M. acknowledges Secretaria d'Universitats i 1063 Recerca del Departament d'Economia i Coneixement de la Generalitat de Catalunya 1064 (expedient number 2013 CTP 00013) and the Erasmus+ program from the UAB for 1065 funding used for visiting collections at the Institut des Sciences de l’Evolution de 1066 Montpellier (Université Montpellier, France). J.F. is supported by the Spanish Agencia 1067 Estatal de Investigación and the European Regional Development Fund of the European 1068 Union (AEI/FEDER EU, project CGL2017-82654-P). J.F. and O.O. are members of the 1069 consolidated research groups (GRC) 2017 SGR 86 and 1666, respectively, of the 1070 Generalitat de Catalunya. A.B. work is supported by a Juan de la Cierva Incorporación 1071 Fellowship (IJC2018-037685-I, funded by Ministerio de Ciencia e Innovación of the 1072 Spanish Government). We acknowledge support from the CERCA programme (ICP) 1073 from the Generalitat de Catalunya, and the projects “Evolució dels ecosistemes amb 1074 faunes de vertebrats del Permià i el Triàsic de Catalunya” (ref. 2014/100606) and 1075 “Evolució dels ecosistemes durant la transició Paleozoic–Mesozoic a Catalunya” (ref. 1076 CLT009/18/00066), based at the ICP and financially supported by the Departament de 1077 Cultura (Generalitat de Catalunya). We acknowledge the reviewers Lorenzo Marchetti 1078 and Hendrik Klein and the editor Prof. Howard Falcon-Lang, whose comments and 1079 suggestions highly improved a previous version of the manuscript. 1080 1081 References 1082 Abel. O., 1926. Der erste Fund einer Tetrapodenfährte in den unteren alpinen Trias. Pal. 1083 Z. 7, 22–24. 1084 Alroy, J., 2013. Online paleogeographic map generator. http://paleodb.org/?a=mapForm 1085 Avanzini, M., 2000. Synaptichnium tracks with skin impressions from the Anisian 1086 (Middle Triassic) of the Southern Alps (Val di Non – Italy). Ichnos 7(4), 243–251. 32 1087 Avanzini, M., Mietto, P., 2008. Lower and Middle Triassic footprint-based 1088 biochronology in the Italian Southern Alps. Oryctos 8, 3–13. 1089 Avanzini, M., Renesto, S., 2002. A review of Rhynchosauroides tirolicus Abel, 1926 1090 ichnospecies (Middle Triassic: Anisian-Ladinian) and some inferences on 1091 Rhynchosauroides trackmaker. Riv. Ital. Paleontol. S. 108(1), 51–66. 1092 Avanzini, M., Piñuela, L., Garcia-Ramos, J.C., 2010. First report of a Late Jurassic 1093 lizard-like footprint (Asturias, Spain). J. Iber. Geol. 36(2), 175–180. 1094 https://doi.org/10.5209/rev_JIGE.2010.v36.n2.5 1095 Avanzini, M., Bernardi, M., Nicosia, U., 2011. The Permo-Triassic tetrapod faunal 1096 diversity in the Italian Southern Alps, in: Dar, I.A. (Ed.), Earth and Environmental 1097 Sciences. InTech, pp. 591–608. 1098 Benton, M.J., 2016. The Triassic. Curr. Biol. 26, R1205–R1225. 1099 Benton, M.J., 2018. Hyperthermal-driven mass extinctions: killing models during the 1100 Permian–Triassic mass extinction. Phil. Trans. R. Soc. A 376: 20170076. 1101 https://doi.org/10.1098/rsta.2017.0076 1102 Benton, M.J., Newell, A.J., 2014. Impacts of global warming on Permo-Triassic 1103 terrestrial ecosystems. Gondwana Res. 25, 1308–1337. 1104 https://doi.org/10.1016/j.gr.2012.12.010 1105 Bernardi, M., Klein, H., Petti, F.M., Ezcurra, M.D., 2015. The origin and early radiation 1106 of archosauriforms: integrating the skeletal and footprint record. PLoS ONE 10 (6), 1107 e0128449. 1108 Bernardi, M., Gianolla, P., Petti, F.M, Mietto, P., Benton, M.J., 2018. Dinosaur 1109 diversification linked with the Carnian Pluvial Episode. Nat. Commun. 9, 1499. 1110 https://doi.org/10.1038/s41467-018-03996-1 1111 Bernardi, M., Petti, F.M., Simões, T.R., 2019. No longer in the Mesozoic. The Permian 1112 world as a cradle for the origin of key vertebrate groups. Permophiles 67, 29–31. 1113 Berrocal-Casero, M., Arribas, M., Moratalla, J.J., 2018a. Didactic and divulgative 1114 resources of the Middle Triassic vertebrate Tracksite of Los Arroturos (Province of 1115 Guadalajara, Spain). Geoheritage 10, 375–384. https://doi.org/10.1007/s12371-017- 1116 0244-1 1117 Berrocal-Casero, M., Audije-Gil, J., Castanhinha, R.A., Pérez-Valera J.A., dos Santos, 1118 V. F., Segura M., 2018b. New discoveries of vertebrate remains from the Triassic 1119 of Riba de Santiuste, Guadalajara (Spain). P. Geologist Assoc. 129, 526–541. 1120 https://doi.org/10.1016/j.pgeola.2018.04.009 33 1121 Bourquin, S., Bercovici, A., López-Gómez, J., Diez, J.B., Broutin, J., Ronchi, A., 1122 Durand, M., Arche, A., Linol, B., Amour, F., 2011. The Permian-Triassic transition 1123 and the onset of Mesozoic sedimentation at the northwestern peri-Tethyan domain 1124 scale: Palaeogeographic maps and geodynamic implications. Palaeogeogr. 1125 Palaeoclimatol. Palaeoecol. 299, 265–280. 1126 https://doi.org/10.1016/j.palaeo.2010.11.007 1127 Brusatte, S. L., Niedźwiedzki, G., and Butler, R. J. 2011. Footprints pull origin and 1128 diversification of dinosaur stem lineage deep into Early Triassic. Proc. R. Soc. B 1129 278, 1107–1113. https://doi.org/10.1098/rspb.2010.1746 1130 Butler, R.J., Brusatte, S.L., Reich, M., Nesbitt, S.J., Schoch, R.R., Hornung, J.J., 2011. 1131 The sail-backed reptile Ctenosauriscus from the latest Early Triassic of Germany 1132 and the timing and biogeography of the early archosaur radiation. PLoS ONE 6(10), 1133 e25693. https://doi.org/10.1371/journal.pone.0025693 1134 Calvet, F., Marzo, M., 1994. El Triásico de las Cordilleras Costero Catalanas: 1135 Estratigrafía, Sedimentología y Análisis Secuencial. Cuaderno de Excursión. III 1136 Coloquio de Estratigrafía y Paleoestratigrafía del Pérmico y Triásico de España. 1137 Field Guide, 1–53. 1138 Calvet, F., Tucker, M.E., Henton, J.M., 1990. Middle Triassic carbonate ramp systems 1139 in the Catalan Basin, northeast Spain: facies, systems tracts, sequences and 1140 controls. Special Publications International Association of Sedimentology, 9, 79- 1141 108. 1142 Carmona N., Bournod, C., Ponce, J.J., Cuadrado D., 2011. The role of microbial mats in 1143 the preservation of bird footprints: a case study from the mesotidal Bahia Blanca 1144 estuary (Argentina). SEPM Special Publications 101, 37–45. 1145 https://doi.org/10.2110/sepmsp.101.037 1146 Cavicchini, I., Zaher, M., Benton, M.J., 2020. An enigmatic neodiapsid reptile from the 1147 Middle Triassic of England. J. Vertebr. Paleontol., e1781143, 18 pp. 1148 https://doi.org/10.1080/02724634.2020.1781143. 1149 Cavin, L., Piuz, A., 2020. A Several-Kilometer-Long Archosaur Route in the Triassic of 1150 the Swiss Alps. Front. Earth Sci. 8, 4. https://doi.org/10.3389/feart.2020.00004 1151 Citton, P., Ronchi, A., Nicosia, U., Sacchi, E., Maganuco, S., Cipriani, A., Innamorati, 1152 G., Zuccari, C., Manucci, F., Romano, M., 2020. Tetrapod tracks from the Middle 1153 Triassic of NW Sardinia (Nurra region, Italy). Ital. J. Geosci. 139, 309–320. 1154 https://doi.org/10.3301/IJG.2020.07 34 1155 Damiani, R., Schoch, R.R., Hellrung, H., Werneburg, R., Gastou, S., 2009. The 1156 plagiosaurid temnospondyl Plagiosuchus pustuliferus from the Middle Triassic of 1157 Germany: anatomy and functional morphology of the skull. Zool. J. Linn. Soc. 155, 1158 348–373. https://doi.org/10.1111/j.1096-3642.2008.00444.x 1159 De Jaime-Soguero, C., Mujal, E., Fortuny, J., 2020. First xiphosuran traceway in the 1160 middle Muschelkalk facies (Middle Triassic) of the Catalan Basin (NE Iberian 1161 Peninsula). Spanish J. Palaentol. 35 (2), 197–208. 1162 https://doi.org/10.7203/sjp.35.2.18483 1163 Demathieu, G. 1966. Rhynchosauroides petri et Sphingopus ferox, nouvelles empreintes 1164 de reptiles des grès Triasiques de la bordure Nord-Est du Massif Central. C. R. 1165 Acad. Sci. Paris D 263, 483–486. 1166 Demathieu, G., 1970. Les empreintes de pas de vertébrés du Trias de la bordure nord-est 1167 du Massif Central. Cahiers de Paleontologie, 1–211. 1168 Demathieu, G., 1985. Trace fossil assemblages in middle Triassic marginal marine 1169 deposits, Eastern border of the Massif Central, France. In: Curren, H.A. (Ed.), 1170 Biogenic structures. SEPM Special Publications 35, 53–66. 1171 Demathieu, G., Demathieu, P., 2004. Chirotheria and Other Ichnotaxa of the European 1172 Triassic. Ichnos 11(1-2), 79–88. https://doi.org/10.1080/10420940490444898 1173 Demathieu, G., Durand, M., 1991. Les traces de pas de Tétrapodes dans le Trias 1174 détritique du Car et des Alpes-Maritimes (France). Bull. Soc. His. Nat. Autun 32, 1175 4–18. 1176 Demathieu, G., Oosterink, H.W., 1983. Die Wirbeltier–Ichnofauna aus dem Unteren 1177 Muschelkalk von Winterswijk (Die Reptilfährten aus der Mitteltrias der 1178 Niederlande). Staringia 7, 1–51. 1179 Demathieu, G., Oosterink, H.W., 1988. New discoveries of ichnofossils from the 1180 Middle Triassic of Winterswijk (The Netherlands). Geol. Mijnbouw 67(1), 3–17. 1181 Demathieu, G., Ramos, A., Sopeña, A., 1978. Fauna icnológica del Triásico del extremo 1182 noroccidental de la Cordillera Ibérica (Provincia de Guadalajara). Estud. Geol. 34, 1183 175–186. 1184 Díaz-Martínez, I., Pérez-García, A., 2012. Historical and comparative study of the first 1185 Spanish vertebrate paleoichnological record and bibliographic review of the 1186 Spanish chiroteroiid footprints. Ichnos 19, 141–149. 1187 https://doi.org/10.1080/10420940.2012.685565 35 1188 Díaz-Martínez, I., Castanera, D., Gasca, J.M., Canudo, J.I., 2015. A reappraisal of the 1189 Middle Triassic chirotheriid Chirotherium ibericus Navas, 1906 (Iberian Range NE 1190 Spain), with comments on the Triassic tetrapod track biochronology of the Iberian 1191 Peninsula. PeerJ 3, e1044. https://doi.org/10.7717/peerj.1044 1192 Diedrich, C., 2002. Vertebrate track bed stratigraphy at new megatrack sites in the 1193 Upper Wellenkalk Member and orbicularis Member (Muschelkalk, Middle 1194 Triassic) in carbonate tidal flat environments of the western Germanic Basin. 1195 Palaeogeogr. Palaeoclimatol. Palaeoecol. 183, 185–208. 1196 https://doi.org/10.1016/S0031-0182(01)00467-9 1197 Diedrich, C., 2008. Millions of reptile tracks – Early to Middle Triassic carbonate tidal 1198 flat migration bridges of Central Europe- reptile immigration into the Germanic 1199 Basin. Palaeogeogr. Palaeoclimatol. Palaeoecol. 259, 410–423. 1200 https://doi.org/10.1016/j.palaeo.2007.09.019 1201 Diedrich, C., 2012. Middle Triassic chirotherid trackways on earthquake influenced 1202 intertidal limulid reproduction flats of the European Germanic Basin coasts. Cent. 1203 Eur. J. Geosci. 4(3), 495–529. https://doi.org/10.2478/s13533-011-0080-9 1204 Diedrich, C., 2015. Isochirotherium trackways, their possible trackmakers 1205 (?Arizonasaurus): intercontinental giant archosaur migrations in the Middle 1206 Triassic tsunami-influenced carbonate intertidal mud flats of the European 1207 Germanic Basin. Carbonates Evaporites 30, 229–252. 1208 https://doi.org/10.1007/s13146-014-0228-z 1209 Dinarès-Turell, J., Díez, B.J., Rey, D., Arnal, I., 2005. “Buntsandstein” 1210 magnetostratigraphy and biostratigraphic reappraisal from eastern Iberia: Early and 1211 Middle Triassic stage boundary definitions through correlation to Tethyan sections. 1212 Palaeogeogr. Palaeoclimatol. Palaeoecol. 229, 158–77. 1213 https://doi.org/10.1016/j.palaeo.2005.06.029 1214 Escudero-Mozo, M.J., Márquez-Aliaga, A., Goy, A., Martín-Chivelet, A., López- 1215 Gómez, J., Márquez, L., Arche, A., Plasencia, P., Pla, C., Marzo, M., Sánchez- 1216 Fernández, D. (2015) Middle Triassic carbonate platforms in eastern Iberia: 1217 Evolution of their fauna and palaeogeographic significance in the Western Tethys. 1218 Palaeogeogr. Palaeoclimatol. Palaeoecol. 417, 236–260. 1219 https://doi.org/10.1016/j.palaeo.2014.10.041 1220 Ezcurra, M.D., 2010. Biogeography of Triassic tetrapods: evidence for provincialism 1221 and driven sympatric cladogenesis in the early evolution of modern tetrapod 36 1222 lineages. Proc. R. Soc. B 277(1693), 2547–2552. 1223 https://doi.org/10.1098/rspb.2010.0508 1224 Ezcurra, M.D., 2016. The phylogenetic relationships of basal archosauromorphs, with 1225 an emphasis on the systematics of proterosuchian archosauriforms. PeerJ 4, e1778. 1226 https://doi.org/10.7717/peerj.1778 1227 Ezcurra, M.D., Butler, R.J., 2015. Taxonomy of the proterosuchid archosauriforms 1228 (Diapsida: Archosauromorpha) from the earliest Triassic of South Africa, and 1229 implications for the early archosauriform radiation. Palaeontology 58(1), 141–170. 1230 https://doi.org/10.1111/pala.12130 1231 Ezcurra, M.D., Butler, R.J., 2018. The rise of the ruling reptiles and ecosystem recovery 1232 from the Permo-Triassic mass extinction. Proc. R. Soc. B 285, 20180361. 1233 https://doi.org/10.1098/rspb.2018.0361 1234 Falkingham, P.L., 2012. Acquisition of high resolution 3D models using free, open- 1235 source, photogrammetric software. Paleontol. Electron. 15, 1–15. https://doi.org/ 1236 10.26879/264 1237 Falkingham, P.L., 2014. Interpreting ecology and behaviour from the vertebrate fossil 1238 track record. J. Zool. 292, 222–228. https://doi.org/10.1111/jzo.12110 1239 Farman, R.M., Bell, P.R., 2020. Australia’s earliest tetrapod swimming traces from the 1240 Hawkesbury Sandstone (Middle Triassic) of the Sydney Basin. J. Paleontol. 94(5), 1241 966–978. https://doi.org/10.1017/jpa.2020.22 1242 Fichter, J., Kunz, R., 2004. New genus and species of chirotheroid tracks in the 1243 Detfurth-Formation (Middle Bunter, Lower Triassic) of Central Germany. Ichnos 1244 11, 183–193. https://doi.org/10.1080/10420940490444997 1245 Fortuny, J., Bolet, A., Sellés, A.G., Cartanyà, J., Galobart, À., 2011a. New insights on 1246 the Permian and Triassic vertebrates from the Iberian Peninsula with emphasis on 1247 the Pyrenean and Catalonian basis. J. Iber. Geol. 37(1), 65–86. 1248 https://doi.org/:10.5209/rev_JIGE.2011.v37.n1.5 1249 Fortuny, J., Galobart, À., De Santisteban, C., 2011b. A new capitosaur from the Middle 1250 Triassic of Spain and the relationships within the Capitosauria. Acta Palaeontol. 1251 Pol. 56(3), 553–566. https://doi.org/10.4202/app.2010.0025 1252 Foth, C., Ezcurra, M.D., Sookias, R.B., Brusatte, S.L., Butler, R.J., 2016. Unappreciated 1253 diversification of stem archosaurs during the Middle Triassic predated the 1254 dominance of dinosaurs. BMC Evol. Biol. 16, 188. https://doi.org/10.1186/s12862- 1255 016-0761-6 37 1256 Franz, M., Henniger, M., Barnasch, J., 2013. The strong diachronous 1257 Muschelkalk/Keuper facies shift in the Central European Basin: implications from 1258 the type-section of the Erfurt Formation (Lower Keuper, Triassic) and basin-wide 1259 correlations. Int. J. Earth Sci. 102, 761–780. https://doi.org/10.1007/s00531-012- 1260 0823-y 1261 Franz, M., Kaiser, S.I., Fischer, J., Heunisch, C., Kustatscher, E., Luppold, F.W., 1262 Berner, U., Röhling, H.G., 2015. Eustatic and climatic control on the Upper 1263 Muschelkalk Sea (late Anisian/Ladinian) in the Central European Basin. Global 1264 Planet. Change 135, 1–27. https://doi.org/10.1016/j.gloplacha.2015.09.014 1265 Galán-Abellán, B., López-Gómez, J., Barrenecha, J.F., Marzo, M., De la Horra, R., 1266 Arche, A., 2013. The beginning of the Buntsandstein cycle (Early-Middle Triassic) 1267 in the Catalan Ranges, NE Spain: Sedimentary and palaegeographic implications. 1268 Sediment. Geol. 296, 86–102. https://doi.org/10.1016/j.sedgeo.2013.08.006 1269 Gand, G., Demathieu, G., Montenat, C., 2007. Les traces de pas d'amphibiens, de 1270 dinosaures et autres reptiles du Mésozoïque français: Inventaire et interprétations. 1271 Palaeovertebrata 35(1–4), 1–149. https://doi.org/10.18563/pv.35.1-4.1-149 1272 Gand, G., De La Horra, R., Galán-Abellán, B., López-Gómez, J., Barrenechea, J. F., 1273 Arche, A., Benito, I., 2010. New ichnites from the Middle Triassic of the Iberian 1274 Ranges (Spain): paleoenvironmental and paleogeographical implications. Hist. 1275 Biol. 22(1–3), 40–56. https://doi.org/10.1080/08912961003644096 1276 Haubold, H., 1967. Eine Pseudosuchier-Fährtenfauna aus dem Buntsandstein 1277 Südthüringens. Hallesches Jb. mitteldt. Erdgesch. 8, 12–48. 1278 Haubold, H., 1971a. Ichnia Amphibiorum et Reptiliorum fossilium. Encyclopedia of 1279 Paleoherpetology, 18. Gustav Fischer Verlag, Stuttgart, Germany, and Portland, 1280 USA. 1281 Haubold, H., 1971b. Die Tetrapodenfährten des Buntsandsteins in der Deutschen 1282 Demokratischen Republik und in Westdeutschland und ihre Äquivalente in der 1283 gesamten Trias. Paläntologische Abhandlungen, Abteilung A Paläozoologie, 395– 1284 548. 1285 Haubold, H., 1984. Saurierfährten (2nd ed.). Die Neue Brehm-Bucherei 479, 1286 Wittenberg (Ziemsen). 1287 Haubold, H., 1999. Tracks of the Dinosauromorpha from the Early Triassic, in 1288 Bachmann, G.H., Lerche, I. (Eds.), Triassic. Zentralbl. Geol. Paläont., Teil I, 1998 1289 (7–8), Stuttgart, pp. 783–795. 38 1290 Haubold, H., 2006. Die Saurierfährten Chirotherium barthii Kaup, 1835 – das 1291 Typusmaterial aus dem Buntsandstein bei Hildburghausen/Thüringen und das 1292 Chirotherium–Monument. Veröffentlichungen Naturhist. Museum Schleusingen 1293 21, 3–31. 1294 Haubold, H., Klein, H., 2000. Die dinosauroiden Fährten Parachirotherium–Atreipus– 1295 Grallator aus dem unteren Mittelkeuper (Obere Trias: Ladin, Karn, ?Nor) in 1296 Franken: Hallesches Jahrb. Geowiss. B 22, 59–85. 1297 Haubold, H., Klein, H., 2002. Chirotherien und Grallatoriden aus der Unteren bis 1298 Oberen Trias Mitteleuropas und die Entstehung der Dinosauria. Hallesches Jahrb. 1299 Geowiss. B 24, 1–22. 1300 Holst, H.K.H., Smit, J., Veenstra, E., 1970. Lacertoid footprints from the Early Middle 1301 Triassic at Haarmuhle, near Altstatte, W. Germany. Proc. K. Ned. Akad. van Wet. 1302 B 73(2), 157–165. 1303 Hunt, A.P., Lucas, S.G., 2007a. Tetrapod ichnofacies: a new paradigm. Ichnos 14, 59– 1304 68. https://doi.org/10.1080/10420940601006826 1305 Hunt, A.P., Lucas, S.G., 2007b. The Triassic tetrapod track record: Ichnofaunas, 1306 ichnofacies and biochronology. N. M. Mus. Nat. Hist. Sci. Bull. 41, 78–87. 1307 Irmis, R.B., Whiteside, J.H., 2012. Delayed recovery of non-marine tetrapods after the 1308 end-Permian mass extinction tracks global carbon cycle. Proc. R. Soc. B 279, 1309 1310–1318. https://doi.org/10.1098/rspb.2011.1895 1310 Klausen, T.G., Paterson, N.W., Benton, M.J., 2020. Geological control on dinosaurs’ 1311 rise to dominance: Late Triassic ecosystem stress by relative sea level change. 1312 Terra Nova. https://doi.org/10.1111/TER.12480 1313 Kaup, J.J., 1835. Fährten von Beuteltieren. Das Tierreich, 246–248. 1314 Klein, H., Haubold, H., 2003. Differenzierung von ausgewählten Chirotherien der Trias 1315 mittels Landmarkanalyse. Hallesches Jahrb. Geowiss. B 25, 21–36. 1316 Klein, H., Haubold, H., 2007. Archosaur footprints –potential for biochronology of 1317 Triassic continental sequences, in: Lucas, S.G., Spielmann, J.A. (Eds.), The Global 1318 Triassic. N. M. Mus. Nat. Hist. Sci. Bull. 41, 120–130. 1319 Klein, H., Lucas, S.G., 2010a. Review of the tetrapod ichnofauna of the Moenkopi 1320 Formation/group (Early-Middle Triassic) of the American Southwest. N. M. Mus. 1321 Nat. Hist. Sci. Bull. 50, 1–67. 39 1322 Klein, H., Lucas, S.G., 2010b. Tetrapod footprints – their use in biostratigraphy and 1323 biochronology of the Triassic. Geol. Soc. Lond., Spec. Publ. 334, 419–446. 1324 https://doi.org/10.1144/SP334.14 1325 Klein, H., Lucas, S.G., 2018. Diverse Middle Triassic tetrapod footprints assemblage 1326 from the Muschelkalk of Germany. Ichnos 25, 162–176. 1327 https://doi.org/10.1080/10420940.2017.1337632 1328 Klein, H., Niedźwiedzki, G., 2012. Revision of the Lower Triassic tetrapod ichnofauna 1329 from Wióry, Holy Cross Mountains, Poland. N. M. Mus. Nat. Hist. Sci. Bull. 56, 1– 1330 62. 1331 Klein, H., Voigt, S., Saber, H., Schneider, J.W., Hminna, A., Fischer, J., Lagnaoui A., 1332 Brosig, A., 2011. First occurrence of a Middle Triassic tetrapod ichnofauna from 1333 the Argana Basin (Western High Atlas, Morocco). Palaeogeogr. Palaeoclimatol. 1334 Palaeoecol. 307, 218–231. https://doi.org/10.1016/j.palaeo.2011.05.021 1335 Klein, H., Niedźwiedzki, G., Voigt, S., Lagnaoui, A., Hminna, A., Saber, H., Schneider, 1336 J.W., 2013. The tetrapod ichnogenus Protochirotherium Fichter and Kunz 2004, a 1337 characteristic Early Triassic morphotype of Central Pangea. Ichnos 20, 24–30. 1338 https://doi.org/10.1080/10420940.2012.757699 1339 Klein, H., Lucas, S.G., Voigt, S., 2015. Revision of the Permian-Triassic Tetrapod 1340 Ichnogenus Procolophonichnium Nopcsa 1923 with description of the new 1341 ichnospecies P. lockleyi. Ichnos 22(3-4), 155–176. 1342 https://doi.org/10.1080/10420940.2015.1063490 1343 Klein, H., Wizevich, M.C., Thüring, B., Marty, D., Thüring, S., Falkingham, P., Meyer, 1344 C.A., 2016. Triassic chirotheriid footprints from the Swiss Alps: ichnotaxonomy 1345 and depositional en-vironment (Cantons Wallis & Glarus). Swiss J. Palaeontol. 1346 135(2), 295–314. https://doi.org/10.1007/s13358-016-0119-0 1347 Kotański, Z., Gierliński, G., Ptaszyński, T., 2004. Reptile tracks (Rotodactylus) from the 1348 Middle Triassic of the Djurdjura Mountains in Algeria. Geol. Q. 48(1), 89–96. 1349 Lagnaoui, A., Melchor, R.N., Bellosi, E., Villegas, P., 2019. Middle Triassic 1350 Pentasauropus-dominated ichnofauna from the western Gondwana: 1351 Ichnotaxonomy, palaeoenvironment, biostratigraphy and palaeobiogeograpgy. 1352 Palaeogeogr. Palaeoclimatol. Palaeoecol. 524, 41–61. 1353 https://doi.org/10.1016/j.palaeo.2019.03.020 40 1354 Leonardi, G., 1980. Isochirotherium sp.: pista de um gigantesco tecodonte na Formação 1355 Antenor Navarro (Triássico), Sousa, Paraíba, Brasil. Revista Brasileira de 1356 Geociências10, 186–190. 1357 Leonardi, G., 1987. Glossary and Manual of Tetrapod Footprint Palaeoichnology. 1358 Departamento Nacional de Produção Mineral, Brasilia. 1359 Lichtig, A.J., Lucas, S.G., Klein, H., Lovelace, D.M., 2018. Triassic turtle tracks and 1360 the origin of turtles. Hist. Biol. 30 (8), 1112–1122. 1361 https://doi.org/10.1080/08912963.2017.1339037 1362 López-Gómez, J., Arche, A., Pérez-López, A., 2002. Permian and Triassic, in: Gibbons, 1363 W., Moreno, M.T. (Eds.), The Geology of Spain. Geological Society of London, 1364 London, pp. 185–212. 1365 Lovelace, D.M., Lovelace, S.D., 2012. Paleoenvironments and paleoecology of a Lower 1366 Triassic invertebrate and vertebrate ichnoassemblage from the Red Peak Formation 1367 (Chugwater Group), Central Wyoming. Palaios 27, 636–657. https://doi.org/ 1368 10.2307/23362122 1369 Lucas, S.G., 2010. The Triassic timescale based on nonmarine tetrapod biostratigraphy 1370 and biochronology. Geological Society, London, Special Publications 334, 447– 1371 500. https://doi.org/10.1144/SP334.15 1372 Lucas, S.G., 2017. Permian tetrapod extinction events. Earth-Sci. Rev. 170, 31–60. 1373 https://doi.org/10.1016/j.earscirev.2017.04.008 1374 Lucas S.G., 2018. Permian tetrapod biochronology, correlation and evolutionary events. 1375 Geological Society, London, Special Publications 450, 405–444. 1376 https://doi.org/10.1144/SP450.12 1377 Lucas, S.G., 2019. An ichnological perspective on some major events of Paleozoic 1378 tetrapod evolution. Boll. Soc. Paleont. Ital. 58(3), 223–266. 1379 https://doi.org/10.4435/BSPI.2019.20 1380 MacDougall, M.J., Brocklehurst, N., Fröbisch, J., 2019. Species richness and disparity 1381 of parareptiles across the end-Permian mass extinction. Proc. R. Soc. B 286, 1382 20182572. https://doi.org/10.1098/rspb.2018.2572 1383 Maidwell F., 1911. Notes on footprints from the Keuper of Runcorn Hill. Liverpool 1384 Geological Society 11,140–152. 1385 Mallison, H., Wings, O., 2014. Photogrammetry in Paleontology, a practical guide. J. 1386 Paleontol. Tech. 12, 1–31. 41 1387 Manzanares, E., Escudero-Mozo, M.J., Ferrón, H., Martínez-Pérez, C., Botella, H., 1388 2020. Middle Triassic sharks from the Catalan Coastal ranges (NE Spain) and 1389 faunal colonization patterns during the westward transgression of Tethys. 1390 Palaeogeogr. Palaeoclimatol. Palaeoecol. 539, 109489. 1391 https://doi.org/10.1016/j.palaeo.2019.109489 1392 Marchetti, L., Tessarollo, A., Felletti, F., Ronchi, A., 2017. Tetrapod footprint 1393 paleoecology: behavior, taphonomy and ichnofauna disentangled. A case study 1394 from the Lower Permian of the Southern Alps (Italy). Palaios 32, 506–527. 1395 https://doi.org/10.2110/palo.2016.108 1396 Marchetti, L., Belvedere, M., Voigt, V., Klein, H., Castanera, D., Díaz-Martínez, I., 1397 Marty, D., Xing, L., Feola, S., Melchor, R.N., Farlow, J.O., 2019b. Defining the 1398 morphological quality of fossil footprints. Problems and principles of preservation 1399 in tetrapod ichnology with examples from the Palaeozoic to the present. Earth-Sci. 1400 Rev. 193, 109–145. https://doi.org/10.1016/j.earscirev.2019.04.008 1401 Marchetti, L., Van Der Donck, H., Van Hylckama Vlieg, M., During, M.A.D., 2019c. 1402 Leaving only trace fossils - the unknown visitors of Winterswijk. Grondboor & 1403 Hamer, Staringia 16, 250–257. 1404 Marchetti, L., Voigt, S., Klein, H., 2019d. Revision of Late Permian tetrapod tracks 1405 from the Dolomites (Trentino-Alto Adige, Italy). Hist. Biol. 31(6), 748–783. 1406 https://doi.org/10.1080/08912963.2017.1391806 1407 Marchetti, L., Voigt, S., Lucas, S.G., Francischini, H., Dentzien-Dias, P., Sacchi, R., 1408 Mangiacotti, M., Scali, S., Gazzola, A., Ronchi, A., Millhouse, A. 2019a. Tetrapod 1409 ichnotaxonomy in eolian paleoenvironments (Coconino and De Chelly formations, 1410 Arizona) and late Cisuralian (Permian) sauropsid radiation. Earth-Sci. Rev. 190, 1411 148–170. https://doi.org/10.1016/j.earscirev.2018.12.011 1412 Marchetti, L., Klein, H., Falk, D., Wings, O., 2020. Synaptichnium tracks from the 1413 Middle Muschelkalk (Middle Triassic, Anisian) Bernburg site (Saxony-Anhalt, 1414 Germany). Ann. Soc. Geol. Pol. 90, 12 pp. https://doi.org/10.14241/asgp.2020.12 1415 Maron, M., Muttoni, G., Rigo, M., Gianolla, P., Kent, D.V., 2019. New 1416 magnetobiostratigraphic results from the Ladinian of the Dolomites and 1417 implications for the Triassic geomagnetic polarity timescale. Palaeogeogr. 1418 Palaeoclimatol. Palaeoecol. 517, 52–73. 1419 https://doi.org/10.1016/j.palaeo.2018.11.024 42 1420 Márquez-Aliaga, A., Valenzuela-Rios, J.I., Calvet, F., Budurov, K., 2000. Middle 1421 Triassic conodonts rom northeastern Spain; biostratigraphic implications. Terra 1422 Nova 12, 77– 83. 1423 Marsicano, C.A., Arcuci, A.B., Mancuso, A.C., Caselli, A.T., 2004. Middle Triassic 1424 tetrapod footprints of southern South America. Ameghiniana 41(2), 171–184. 1425 Marsicano, C.A., Wilson, J.A., Smith, R.M.H., 2014. A temnospondyl trackway from 1426 the early Mesozoic of Western Gondwana and its implications for basal tetrapod 1427 locomotion. PLoS ONE 9, e103255. https://doi.org/10.1371/journal.pone.0103255 1428 Marty, D., Strasser, A., Meyer, C.A., 2009. Formation and Taphonomy of Human 1429 Footprints in Microbial Mats of Present-Day Tidal-flat Environments: Implications 1430 for the Study of Fossil Footprints. Ichnos 16(1–2), 127–142. 1431 https://doi.org/10.1080/10420940802471027 1432 Marzo, M., 1980. El Buntsandstein de las Catalánides: estratigrafía y procesos de 1433 sedimentación. [PhD Tesis], 1–634. 1434 Melchor, R.N., 2015. Application of vertebrate trave fossils to paleoenvironmental 1435 analysis. Palaeogeogr. Palaeoclimatol. Palaeoecol. 439, 79–96. 1436 https://doi.org/10.1016/j.palaeo.2015.03.028. 1437 Melchor, R. N., Sarjeant, W.A.S., 2004. Small amphibian and reptile footprints from the 1438 Permian Carapacha Basin, Argentina. Ichnos 11, 57–78. 1439 https://doi.org/10.1080/10420940490428814. 1440 Melchor, R. N., De Valais, S., 2006. A review of Triassic tetrapod track assemblages 1441 from Argentina. Palaeontology 49, 355–379. https://doi.org/10.1111/j.1475- 1442 4983.2006.00538.x 1443 Mietto, P., Avanzini, M., Belvedere, M., Bernardi, M., Dalla Vecchia, F.M., D'Orazi 1444 Porchetti, S., Gianolla, P., Petti, F.M., 2020. Triassic tetrapod ichnofossils from 1445 Italy: the state of the art, in: Romano, M., Citton, P. (Eds.), Tetrapod ichnology in 1446 Italy: the state of the art. J. Med. Earth Sci. 12, 83–136. 1447 https://doi.org/10.3304/jmes.2020.17066 1448 Morad, S., Al-Aasm, I.S., Longstaffe, F.J., Marfil, R., De Ros, L. F., Johansen, H., 1449 Marzo, M., 1995. Diagenesis of a mixed siliciclastic/evaporitic sequence of the 1450 Middle Muschelkalk (Middle Triassic), the Catalan Coastal Range, NE Spain. 1451 Sedimentology 42, 749–768. https://doi.org/10.1111/j.1365-3091.1995.tb00407.x 1452 Mujal, E., Schoch, R.R., 2020. Middle Triassic (Ladinian) amphibian tracks from the 1453 Lower Keuper succession of southern Germany: Implications for temnospondyl 43 1454 locomotion and track preservation. Palaeogeogr. Palaeoclimatol. Palaeoecol. 543, 1455 109625. https://doi.org/10.1016/j.palaeo.2020.109625 1456 Mujal, E., Fortuny, J., Rodríguez-Salgado, P., Diviu, M., Oms, O., Galobart, À., 2015. 1457 First footprints occurrence from the Muschelkalk detritical unit of the Catalan 1458 Basin: 3D analyses and paleoichnological implications. Spanish J. Palaentol. 30, 1459 97–107. https://doi.org/10.7203/sjp.30.1.17204 1460 Mujal, E., Fortuny, J., Oms, O., Bolet, A., Galobart, À., Anadón, P., 2016a. 1461 Palaeoenvironmental reconstruction of an Early Permian ichnoassemblage from the 1462 NE Iberian Peninsula (Pyrenean Basin). Geol. Mag. 153 (4), 578–600. 1463 https://doi.org/10.1017/S0016756815000576 1464 Mujal, E., Gretter, N., Ronchi, A., López-Gómez, J., Falconnet, J., Diez, J.B., De la 1465 Horra, R., Bolet, A., Oms, O., Arche, A., Barrenechea, JF., Steyer, J-S., Fortuny, J., 1466 2016b. Constraining the Permian/Triassic boundary in continental environments: 1467 stratigraphic and paleontological record from the Southern-Eastern Pyrenees (NE 1468 Iberian Peninsula). Palaeogeogr. Palaeoclimatol. Palaeoecol. 445, 18–37. 1469 https://doi.org/10.1016/j.palaeo.2015.12.008 1470 Mujal, E., Fortuny, J., Bolet, A., Oms, O., López, J.Á., 2017a. An archosauromorph 1471 dominated ichnoassemblage in fluvial settings from the late Early Triassic of the 1472 Catalan Pyrenees (NE Iberian Peninsula). Plos ONE 12(4), e0174693. 1473 https://doi.org/10.1371/journal.pone.0174693 1474 Mujal, E., Fortuny, J., Pérez-Cano, J., Dinarès-Turell, J., Ibáñez-Insa, J., Oms, O., Vila, 1475 I., Bolet, A., Anadón, P., 2017b. Integrated multi-stratigraphic study of the Coll de 1476 Terrers late Permian-Early Triassic continental succession from the Catalan 1477 Pyrenees (NE Iberian Peninsula): A geologic reference record for equatorial 1478 Pangaea. Global Planet. Change 159, 46–60. 1479 https://doi.org/10.1016/j.gloplacha.2017.10.004 1480 Mujal, E., Belaústegui, Z., Fortuny, J., Bolet, A., Oms, O., López, J.Á., 2018b. 1481 Ichnological evidence of a horseshoe crab hot-spot in the Early Triassic 1482 Buntsandstein continental deposits from the Catalan Pyrenees (NE Iberian 1483 Peninsula). J. Iber. Geol. 44, 139–153. https://doi.org/10.1007/s41513-017-0026-2 1484 Mujal, E., Iglesias, G., Oms, O., Fortuny, J., Bolet, A., Méndez, J.M., 2018a. 1485 Rhynchosauroides footprint variability in a Muschelkalk detrital interval late 1486 Anisian-middle Ladinian) from the Catalan Basin (NE Iberian Peninsula). Ichnos 1487 25(2–3), 150–161. https://doi.org/10.1080/10420940.2017.1337571 44 1488 Mujal, E., Marchetti, L., Schoch, R.R., Fortuny, J., 2020. Upper Paleozoic to lower 1489 Mesozoic tetrapod ichnology revisited: Photogrammetry and relative depth pattern 1490 inferences on functional prevalence of autopodial. Front. Earth Sci. 8, 248. 1491 https://doi.org/10.3389/feart.2020.00248 1492 Niedźwiedzki, G., Brusatte, S.L., Butler, R.J., 2013. Prorotodactylus and Rotodactylus 1493 tracks: an ichnological record of dinosauromorphs from the Early–Middle Triassic 1494 of Poland, in: Nesbit, S.J., Desojo, J.B., Irmis, R.B. (Eds.), Anatomy, Phylogeny 1495 and Palaeobiology of Early Archosaurs and their Kin. Geological Society Special 1496 Publications 379. Geological Society of London, London, pp. 319–351. 1497 Niedźwiedzki, G., Soussi, M., Boukhalfa, K., Gierliński, G.D., 2017. Middle-Upper 1498 Triassic and Middle Jurassic tetrapod track assemblages of Southern Tunisia, 1499 Sahara Platform. J. Afr. Earth Sci. 129, 31–44. 1500 https://doi.org/10.1016/j.jafrearsci.2016.12.006 1501 Nopcsa, F.v., 1923. Die Familien der Reptilien. Fortsch. Geol. Paläont. 2, 210. 1502 Ortí, F., Pérez-López, A., Salvany, J.M., 2017. Triassic evaporites of Iberia: 1503 sedimentologic and palaeogeographic implications for the western Neotethys 1504 evolution during the Middle Triassic-Earliest Jurassic. Palaeogeogr. Palaeoclimatol. 1505 Palaeoecol. 471, 157–180. https://doi.org/10.1016/j.palaeo.2017.01.025 1506 Ortí, F., Salvany, J.M., Rosell, L., Castelltort, X., Inglès, M., Playà, E., 2018. Middle 1507 Triassic evaporite sedimentation in the Catalan basin: implications for the 1508 paleogeographic evolution in the NE Iberian platform. Sediment. Geol. 374, 158– 1509 178. https://doi.org/10.1016/j.sedgeo.2018.07.005 1510 Padian, K., 2013. The problem of dinosaur origins: integrating three approaches to the 1511 rise of Dinosauria. Earth Environ. Sci. Trans. R. Soc. Edinb. 103, 1–20. 1512 Peabody, F.E., 1948. Reptile and amphibian trackways from the Moenkopi Formation 1513 of 1514 Arizona and Utah. Univ. Calif. Publ. Bull. Dep. Geol. Sci. 27, 295–468. 1515 Pérez-López A., 1993. Estudio de las huellas de reptil, del icnogénero 1516 Brachychirotherium, encontradas en el Triásico subbético de Cambil (Jaén). Estud. 1517 Geol. 49, 77–83. https://doi.org/10.3989/egeol.93491-2340 1518 Petti F.M., Bernardi M., Kustatscher E., Renesto S., Avanzini M., 2013. Diversity of 1519 continental tetrapods and plants in the Triassic of the Southern Alps: Ichnological, 1520 Paleozoological and Paleobotanical evidence, in: Tanner L.H., Spielmann J.A., 45 1521 Lucas S.G. (Eds.), The Triassic System. N. M. Mus. Nat. Hist. Sci. Bull. 61, pp. 1522 458–484. 1523 Pinheiro, F.L., França, M.A.G., Lacerda, M.B., Butler, R.J., Schultz, C.L., 2016. An 1524 exceptional fossil skull from South America and the origins of the archosauriform 1525 radiation. Sci. Rep. 6, 22817. https://doi.org/10.1038/srep22817 1526 Reolid, J., Reolid, M., 2017. Traces of Floating Archosaurs: An Interpretation of the 1527 enigmatic trace fossils from the Triassic of the Tabular Cover o Southern Spain, 1528 Ichnos 24(3), 222–233. https://doi.org/10.1080/10420940.2016.1265524 1529 Reolid, M., Márquez-Aliaga, A., Belinchón, M., García-Forner, A., Villena, J., 1530 Martínez-Pérez, C., 2018. Ichnological evidence of semi-aquatic locomotion in 1531 early turtles from Eastern Iberia during the Carnian Humid Episode (Late Triassic). 1532 Palaeogeogr. Palaeoclimatol. Palaeoecol. 490, 450–461. 1533 https://doi.org/10.1016/j.palaeo.2017.11.025 1534 Reolid, J., Cardenal, F.J., Reolid, M., Mata, E., 2020. 3D Imaging of southernmost 1535 Triassic archosaur footprints from Europe (Southern Spain). J. Iber. Geol. 46, 145– 1536 161. https://doi.org/10.1007/s41513-020-00125-0 1537 Rieppel, O., Hagdorn, H., 1998. Fossil reptiles from the Spanish Muschelkalk (Mont-ral 1538 and Alcover, Province Tarragona). Hist. Biol. 13(1), 77–97. 1539 https://doi.org/10.1080/08912969809386575 1540 Rieppel, O., 2000. Sauropterygia I: Placodontia, Pachypleurosauria, Nothosauroidea, 1541 Pistosauroidea. In P. Wellnhofer (Ed.), Handbuch der Paläoherpetologie, Teil 12A. 1542 Verlag Dr. Friedrich Pfeil, Munich, pp. 134. 1543 Romano, M., Bernardi, M., Petti, F.M., Rubidge, B., Hancox, J., Benton, M.J., 2020. 1544 Early Triassic terrestrial tetrapod faune: a review. Earth-Sci. Rev. 210, 103331. 1545 https://doi.org/10.1016/j.earscirev.2020.103331 1546 Rühle v. Lilienstern, H., 1939. Fährten und Spuren im Chirotherium-Sandstein von 1547 Südthüringen. Fortschritte der Geologie und Paläontologie 12(40), 293–387. 1548 Ruta, M., Cisneros, J.C., Liebrecht, T., Tsuji, L.A., Müller J., 2011. Amniotes through 1549 major biological crises: faunal turnover among Parareptiles and the end-Permian 1550 mass extinction. Palaeontology 54(5), 1117–1137. https://doi.org/10.1111/j.1475- 1551 4983.2011.01051.x 1552 Schneider, J.W., Lucas, S.G., Scholze, F., Voigt, S., Marchetti, L., Klein, H., Opluštil, 1553 S., Wernerburg, R., Golubevm, V.K., Barrick, J.E., Nemyrovska, T., Ronchi, A., 1554 Day, M.O., Silantiev, V.V., Rößler, R., Saber, H., Linnemann, U., Zharinova, V., 46 1555 Shen, S.-Z., 2020. Late Paleozoic–early Mesozoic continental biostratigraphy— 1556 Links to the Standard Global Chronostratigraphic Scale. Palaeoworld, 29(2), 186– 1557 238. https://doi.org/10.1016/j.palwor.2019.09.001. 1558 Schoch, R.R., Milner, A.R., 2000. Handbuch der Paläoherpetologie 3B: 1559 Stereospondyli.Pfeil, Munich, 203 pp. 1560 Schoch, R.R., Seegis, D., 2016. A Middle Triassic palaeontological gold mine: the 1561 vertebrate deposits of Vellberg (Germany). Palaeogeogr. Palaeoclimatol. 1562 Palaeoecol. 459, 249–267. https://doi.org/10.1016/j.palaeo.2016.07.002 1563 Schoch, R., Sues, H.-D., 2015. A Middle Triassic stem-turtle and the evolution of the 1564 turtle body plan. Nature 523, 584–587. https://doi.org/10.1038/nature14472 1565 Schoch, R.R., Sues, H.-D., 2018. A new lepidosauromorph reptile from the Middle 1566 Triassic (Ladinian) of Germany and its phylogenetic relationships. J. Syst. 1567 Palaeontol. 12, 113–131. https://doi.org/10.1080/02724634.2018.1444619 1568 Schoch, R.R., Ullmann, F., Rozynek, B., Ziegler, R., Seegis, D., Sues, H.-D., 1569 2018. Tetrapod diversity and palaeoecology in the German Middle Triassic (Lower 1570 Keuper) documented by tooth morphotypes. Palaeobio. Palaeoenv. 98, 615–638. 1571 https://doi.org/10.1007/s12549-018-0327-2 1572 Simões, T.R., Caldwell, M.W., Tałanda, M., Bernardi, M., Palci, A., Vernygora, O., 1573 Bernardini, F. Marcini, L., Nydam, R., 2018. The origin of squamates revealed by a 1574 Middle Triassic lizard from the Italian Alps. Nature 557, 706–709. 1575 https://doi.org/10.1038/s41586-018-0093-3 1576 Sobral, G., Simões, T.R., Schoch, R.R., 2020. A tiny new Middle Triassic stem- 1577 lepidosauromorph from Germany: implications for the early evolution of 1578 lepidosauromorphs and the Vellberg fauna. Sci. Rep. 10, 2273. 1579 https://doi.org/10.1038/s41598-020-58883-x 1580 Solé de Porta, N., Calvet, F., Torrento, L., 1987. Análisis palinológico del Triásico de 1581 los Catalanides (NE España). Cuad. Geol. Ibér. 11, 237–254. 1582 Stubbs, T.L., Pierce, S.E., Rayfield, E.J., Anderson, P.S.L., 2013. Morphological and 1583 biomechanical disparity of crocodile-line archosaurs following the end-Triassic 1584 extinction. Proc. R. Soc. B. 280, 20131940. https://doi.org/10.1098/rspb.2013.1940 1585 Sues, H.-D., Fraser, N.C., 2010. Triassic life on land. Columbia University Press. 1586 Sun, Y.D., Joachimski, M.M., Wignall, P.B., Yan, C.B., Chen, Y.L., Jiang, H.S., Wang, 1587 L.D., Lai, X.L., 2012. Lethally hot temperatures during the Early Triassic 1588 Greenhouse. Science 338, 366–370. https://doi.org/10.1126/science.1224126 47 1589 Thomson, T.J., Droser, M.L., 2015. Swimming reptiles make their mark in the Early 1590 Triassic: Delayed ecologic recovery increased the preservation potential of 1591 vertebrate swim tracks. Geology 43(3), 215–218. https://doi.org/10.1130/G36332.1 1592 Valdiserri, D., Avanzini, M., 2007. A tetrapod ichnoassociation from the Middle 1593 Triassic (Anisian, Pelsonian) of Northern Italy. Ichnos 14(1), 105–116. 1594 https://doi.org/10.1080/10420940601010703 1595 Valentini, M., Conti, M. A., Mariotti, N., 2007. Lacertoid footprints of the upper 1596 Permian Arenaria di Val Gardena Formation (Northern Italy). Ichnos, 14(3–4), 1597 193–218. https://doi.org/10.1080/10420940601049974 1598 Xing, L., Klein, H., 2019. Chirotherium and first Asian Rhynchosauroides tetrapod 1599 trackways from the Middle Triassic of Yunnan, China. Hist. Biol. 11 p. 1600 https://doi.org/10.1080/08912963.2019.1661409 1601 Xing, L., Klein, H., Lockley, M.G., Li, J., Zhang, J., Matsukawa, M., Xiao, J., 2013. 1602 Chirotherium trackways from the Middle Triassic of Guizhou, China. Ichnos 20, 1603 99–107. https://doi.org/10.1080/10420940.2013.788505 1604 Xing, L., Klein, H., Lockley, M.G., Wu, X.-c., Benton, M.J., Zeng, R., Romilio, A., 1605 2020. Footprints of marine reptiles from the Middle Triassic (Anisian-Ladinian) 1606 Guanling Formation of Guizhou Province, southwestern China: The earliest 1607 evidence of synchronous style of swimming. Palaeogeogr. Palaeoclimatol. 1608 Palaeoecol. 558, 109943. https://doi.org/10.1016/j.palaeo.2020.109943 1609 1610 Figure captions 1611 1612 Figure 1. Palaeogeographic maps depicting the global occurrences of Middle Triassic 1613 tetrapod tracksites (see Table S1 for references of the tracksites). A. Map of Pangaea at 1614 240 Ma modified from Alroy (2013). B–C. Anisian and Ladinian maps of the Western 1615 Tethys, modified from Manzanares et al. (2020) (see also references therein). 1616 Figure 2. Geographical and geological setting. A. Map of the Iberian Peninsula 1617 (modified from Escudero-Mozo et al., 2015 and Mujal et al., 2018a). B. Geological map 1618 of the Gaià-Montseny domain (modified from Ortí et al., 2018) with the location of the 1619 known tetrapod tracksites and other reference sections from the middle Muschelkalk 1620 facies. C. Synthetic stratigraphic sections of the middle Muschelkalk from the localities 1621 depicted in B with position of track levels. 48 1622 Figure 3. The Penya Rubí locality. A. Stratigraphic interval including the bulk of the 1623 tetrapod footprints on: the dolostone interval of the Arbolí Gypsum (lower arrow), and 1624 the first sandstone stratum of the Guanta Sandstone (upper arrow). B. Finely laminated 1625 dolostone bearing footprints of the Arbolí Gypsum, note the cyclic change of thickness 1626 of the laminae. C. Lateral equivalent of the dolostone in B, displaying cross lamination 1627 and being coarsier (sandier). D. Ripples in red sandstones oriented in opposite 1628 directions, just above the track-bearing dolostone. E. Water escape and load structures 1629 within the red sandstones and mudstones just below the dolostone layers. F. Wrinkle 1630 structures resulting from desiccation of microbial mats (IPS106602). G, H. Footprints 1631 of Rhynchosauroides tirolicus preserved in finely laminated dolostones (IPS106601a; 1632 G), and relatively deeply impressed (IPS106617a; H). 1633 Figure 4. The Puigventós (A) and Montmany (B–J) localities. A. Common aspect of 1634 the Puigventós strata, being partially covered and fragmented. B. Sandstones, with cross 1635 stratification and ripples on top of each stratum, interbedded in red mudstones. C. 1636 Lateral section of IPS120437 displaying parallel lamination at the lower part and 1637 climbing ripples at the upper part; the arrow points to the section of Sphingopus ferox 1638 digit imprints. D. Left pes track of Sphingopus ferox (IPS120433) with the common 1639 preservation state of tracks in Montmany. E. Densely bioturbated sandstone including 1640 vertical and horizontal cylindrical burrows. F. Potential wrinkle structures of a 1641 microbial mat on a fine- to very fine-grained sandstone. G. Desiccation cracks. H. 1642 Potential gypsum moulds (partially recrystallised with calcite). I. Mould of a hopper 1643 crystal. J. Distinct massive carbonate layer (arrow), probably a dolostone, bearing 1644 abundant Rhynchosauroides tirolicus footprints, and likely corresponding to a portion of 1645 the Arbolí Gypsum embedded within Guanta Sandstone siliciclastic red beds. 1646 Figure 5. Middle Muschelkalk (Catalan Basin) tetrapod tracks I. A. Left track of 1647 Procolophonichnium haarmuehlensis with skin impressions in convex hyporelief 1648 (IPS106601b). B. Small right track of P. isp. in convex hyporelief (IPS120440). C. 1649 Trackway of Chelonipus isp. in convex hyporelief (IPS110268). D. Right manus track 1650 of Rhynchosauroides tirolicus with skin impressions in concave epirelief (IPS106605c). 1651 E. Right manus-pes set of Rh. tirolicus in convex hyporelief (IPS106617b). F. Tiny left 1652 manus-pes set of Rh. isp. in concave epirelief (IPS120439). G. Left track of 1653 Rotodactylus isp. in concave epirelief (IPS107033b). 1654 Figure 6. Middle Muschelkalk (Catalan Basin) tetrapod tracks II. A. Two left manus- 1655 pes sets of Chirotherium cf. sickleri (with corresponding 3D colour-depth model) in 49 1656 convex hyporelief (MGSB-26310). B. Left pes track of C. barthii with skin impressions 1657 in convex hyporelief (IPS85803), arrows point to hopper crystal moulds. C. Left pes 1658 track of Isochirotherium cf. coureli, with Rotodactylus isp. tracks (arrows) and 1659 Rhynchosauroides tirolicus above digit IV, in convex hyporelief (portion of 1660 IPS110269). D. Right manus-pes set of Sphingopus ferox (with corresponding 3D 1661 colour-depth model) in convex hyporelief (IPS120435). Roman numbers refer to digit 1662 imprints. 1663 Figure 7. Occurrence of Middle Triassic tetrapod ichnotaxa and morphotypes based on 1664 Tables S1, S2 and S3. A. Percentage of occurrences of each ichnotaxon/morphotype 1665 within every defined palaeoenvironment; the number of total occurrences counted for 1666 each ichnotaxon/morphotype is above each bar; ichnotaxa and morphotype highlight in 1667 grey are those shown in B, whereas the rest are represented in “Others”. B. 1668 Ichnotaxon/morphotype relative proportions (percentages) in each palaeoenvironment; 1669 the graph shows the percentage that each ichnotaxon/morphotype represents in each 1670 setting; above each bar, the number of occurrences recorded in each setting is indicated. 1671 All ichnotaxa/morphotypes with less than 10 occurrences considering all 1672 regions/localities analysed (each being <4% of the total ichnodiversity) are included in 1673 “Others”. Data from both graphs correspond to presence/absence records of each 1674 ichnotaxon/morphotype without considering the absolute number of footprints from the 1675 analysed regions/localities. 1676 Figure 8. Idealised reconstruction of the Middle Triassic palaeoenvironmental settings 1677 showing the relative abundance of representative tetrapod (ichno-) taxa. Presence, 1678 distribution and relative abundance of tetrapod tracks is based on the references of 1679 Table S1, Fig. 7, and discussion in the text. Silhouettes are not to scale. 50