This is the accepted version of the article: Garcia-Artigas, Ruben; Mercedes Martín, Ramon; Cartanyà, Joan; [et al.]. «Faunal composition and paleoenvironmental reconstruction of a Middle-Late Triassic boundary assemblage in the Pyrenean basin (Catalonia, NE Spain)». Journal of Paleontology, (November 2021), p. 1-16. DOI 10.1017/jpa.2021.99 This version is available at https://ddd.uab.cat/record/250775 under the terms of the license 1 Faunal composition and paleoenvironmental reconstruction 2 of a Middle-Late Triassic boundary assemblage in the 3 Pyrenean basin (Catalonia, NE Spain) 4 5 Ruben Garcia-Artigas1,2, Ramon Mercedes-Martín3, Joan Cartanyà4,5, Arnau Bolet4,6, 6 Marc Riccetto4 and Josep Fortuny4* 7 1 8 Water Research Institute (IdRA), University of Barcelona, 08028 Barcelona, Spain. 9 2 10 Mineralogy, Petrology and Applied Geology Department, Faculty of Earth Sciences, 11 University of Barcelona, 08028 Barcelona, Spain 12 3 Departament de Geologia. Unitat d’Estratigrafia. Universitat Autònoma de Barcelona. 13 Cerdanyola del Vallès E-08193, Barcelona, Spain. < info@ramonmercedes.com > 4 14 Institut Català de Paleontologia, Universitat Autònoma de Barcelona. Edifici ICTA-ICP, 15 c/Columnes s/n, Campus de la UAB, 08193, Cerdanyola del Vallès Barcelona, Spain. 16 , , , 17 18 5 Centre d’Història Natural de la Conca de Barberà C/ Pedrera, 2 – 43400 Montblanc,Tarragona, 19 Spain 6 20 School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, 21 Bristol BS8 1RJ, United Kingdom 22 23 * corresponding author. 24 25 Running Header: A Triassic faunal assemblage from the Pyrenees 26 1 27 Abstract.—The Ladinian-Carnian transition in the Tethys domain was accompanied by 28 an important environmental change representing a milestone in the climate evolution of 29 the Triassic. However, estimations on paleodiversity composition and 30 paleoenvironmental conditions across this interval are scarce in marine settings due to 31 the lack of fossil-bearing successions. In this work, a refined paleontological and 32 sedimentological study has allowed to better characterize a well-preserved marine 33 ?Ladinian-Carnian carbonate succession in the South Central Pyrenees (Odèn site, 34 Catalonia, NE Spain). Vertebrate faunas include numerous actinopterygian specimens, 35 forming an assemblage composed of at least four taxa: Peltopleurus cf. P. nuptialis, 36 Saurichthys sp., Colobodus giganteus, and an indeterminate halecomorph. Specimens 37 belonging to the genus Peltopleurus are dominant whereas the long-snouted 38 Saurichthys, the halecomorph and the large-bodied Colobodus giganteus are less 39 abundant. Tetrapod remains are scarcely present and assigned to sauropterygians. 40 Invertebrate faunas include bivalves (Pseudocorbula gregaria) and brachiopods 41 (Lingula sp.). The fossil assemblage was recovered from organic-rich laminated silty 42 mudstone layers. Sedimentological and textural analyses suggest that fossil biotas were 43 deposited below the fair-weather wave base in shallow subtidal coastal settings. These 44 environments were sporadically sourced by silt/ clay. The age of the Odèn site based on 45 the recovered fauna is assigned to the ?late Ladinian – middle Carnian (Middle-Late 46 Triassic), which is in agreement with previously published ages based on palynomorph 47 data. 48 The refined integration of paleontological, sedimentological and biostratigraphic 49 data from the Odèn site and other vertebrate-bearing localities in the Tethys domain can 50 help better constraint the paleoenvironmental conditions and paleogeographical 51 configuration impacting ecosystem diversity during the late Ladinian – Carnian interval. 2 52 53 Introduction 54 55 The Upper Muschelkalk deposits of NE Iberian Peninsula have been historically and 56 largely studied. Paleontological, sedimentological, and chronostratigraphic research 57 conducted, particularly conducted in the Catalan Basin, have been crucial to understand 58 the evolution of the basin and its ecosystems during this time range (e.g. Verneuil, 59 1854; Wurm, 1913; Schmidt, 1935; Virgili, 1958; Hemleben and Freels, 1977; Via- 60 Boada et al., 1977; Calvet et al., 1987, 1990, 2004; Calvet and Tucker, 1988; Calvet and 61 Marzo, 1994; Fortuny et al., 2011; Mercedes-Martín et al., 2013, 2014a,b; Escudero- 62 Mozo et al., 2015; López-Gómez et al., 2019; García-Ávila et al., 2020, and references 63 therein). 64 Some of the most relevant Upper Muschelkalk fossils have been recovered in the 65 classical localities of Mont-ral and Alcover (Catalan Coastal Ranges) (e.g. Via-Boada, 66 1977; Beltan, 1972, 1975, Cartanyà, 1999; Cartanyà et al., 2015). More recently 67 discovered fossil-bearing sites in adjacent areas such as Mora d’Ebre - Camposines have 68 fueled a renewed interest in the paleontological study of their macrofaunal and 69 ichnofossil assemblages (Fortuny et al., 2011; Cartanyà et al., 2019; Mercedes-Martín 70 and Buatois, 2021) (Fig. 1). The Upper Muschelkalk deposits are represented by 71 extensive marine carbonate units of Ladinian (Middle Triassic), and potentially earliest 72 Carnian age based on recent palynological studies (García-Ávila et al., 2020). Faunas 73 recovered at the Mont-ral-Alcover and Mora d’Ebre-Camposines outcrops have been 74 referred to the late Ladinian (Middle Triassic) by Cartanyà et al. (2019). 75 In the present work, a detailed analysis of coeval Middle Triassic carbonate 76 successions has been performed in the nearby Pyrenean basin (NE Iberian Peninsula) 3 77 (Fig. 1). The corresponding sites have been inadequately studied compared with their 78 equivalent counterparts in the Catalan Coastal Ranges (Lehman, 1964; Fréchengues et 79 al., 1990; Fréchengues and Peybernès, 1991a, b; Calvet et al., 1993, 2004; Cartanyà et 80 al., 2011, 2015; Fortuny et al., 2011). 81 In the Pyrenean basin, fossil fishes are poorly known from only two localities 82 (Fig. 1): 1) Vilanova de la Sal, with reports of an actinopterygian fauna not described in 83 detail (Fortuny et al., 2011), and 2) Odèn, with abundant actinopterygian remains. The 84 Odèn locality was firstly reported by Lehman (1964) who described postcranial remains 85 assigned to Acidorhynchus, a genus currently considered a subjective junior synonym of 86 Saurichthys (Wu et al., 2011). Later, additional specimens referred to Saurichtys, as 87 well as to Peltopleuridae, Halecomorpha and to the large-bodied Colobodus were 88 reported from this site (Cartanyà et al., 2011, 2015; Fortuny et al., 2011). 89 The purpose of this work is twofold: 1) to update and summarize the composition 90 of the diverse faunal assemblage from the Ladinian- Carnian transition at the Odèn 91 locality to date, including the description of the most abundant actinopterygian taxon; 92 and 2) discuss the paleontological, chronostratigraphical, and paleoenvironmental 93 implications of this faunal assemblage in the context of adjoining Middle Triassic 94 basins of the Tethys region. 95 96 Geological setting 97 98 On the Iberian Peninsula, the Triassic stratigraphic record can be subdivided into three 99 parts, from the base to the top: Buntsandstein facies (continental clastic sediments 100 forming red beds), Muschelkalk facies (marine carbonates, evaporites and red beds), 101 and Keuper facies (tidal and sabkha deposits) (Virgili et al., 1983; Salvany and Ortí, 4 102 1989; Calvet et al., 1990). From a tectonostratigraphic point of view, the evolution of 103 the Iberian Peninsula during the upper Permian and Mesozoic can be divided into three 104 rifts and their corresponding post-rift stages, which controlled the sedimentation styles. 105 The rift cycle corresponding to the late Permian - Triassic mainly affected the eastern 106 part of the Iberian plate, giving rise to basins that were filled with sediments attributed 107 to the Germanic facies during the late Permian and Triassic (Salas and Casas, 1993; 108 Ramos et al., 1996; Salas et al., 2001). 109 In the South Pyrenean sector (Les Nogueres-Cadí), the Muschelkalk facies lies on 110 top of the Buntsandstein facies (Anisian), which is composed by sandstones, 111 conglomerates, and clay deposits. The Upper Muschelkalk of the South Pyrenean sector 112 is represented by several limestone-marl-dolostone units of Anisian to Ladinian age 113 (Fréchengues et al., 1990, 1991, 1992; Fréchengues and Peybernès, 1991a, b; Calvet et 114 al., 1993). From base to top, the Upper Muschelkalk is an assemblage of marly 115 dolostones, grey limestones, and limestones with laminated dolostones (Fig. 1) 116 deposited in laterally restricted carbonate ramp intertidal to subtidal environments 117 potentially equivalent to those in the Catalan Coastal Ranges. The total thickness of the 118 Upper Muschelkalk facies in the South Pyrenean region ranges between 37 and 108 119 meters according to Calvet et al. (1993). In this sub-basin, the Muschelkalk facies can 120 be subdivided into three lithological units from bottom to top: Marly Dolomites Unit (2 121 to 8 meters thick), Grey Limestone Unit (20 to 70 meters thick) and Laminated 122 Limestone and/or Dolomites Unit (15 to 30 meters thick) (Calvet et al., 2004) (see Fig. 123 1). 124 The studied outcrops at the Odèn locality can be broadly assigned to the 125 Laminated Limestone and/or Dolomites Unit of Calvet et al. (1993), who proposed a 126 late Ladinian – middle Carnian age for these units based on palynological data. 5 127 128 Material and Methods 129 130 A 28.5-meter long composite sedimentary section was logged at the Odèn locality. The 131 base of the section can be found in the kilometric point 29 of L-401 road, between the 132 villages of Coll de Nargó and Odèn (Figs. 1 and 2). Thirteen rock samples were 133 collected for thin-section analyses. Sedimentary textural descriptions were carried out 134 with a Nikon Eclipse 8400 optical microscope, and photomicrographs were taken with 135 an attached Nikon Microphot FX camera. The material studied here was collected 136 starting in 2009 and were followed by some additional paleontological excavations in 137 2010, 2016, and 2020, yielding a total of 450 specimens (see Results section). All field 138 campaigns were performed under legal permits issued by Departament de Cultura of the 139 Generalitat de Catalunya (Catalan local government). Nine actinopterygian specimens 140 (genus Peltopleurus) are described in detail for the first time in this work (IPS85811, 141 IPS86048, IPS106902, IPS106957, IPS106977, IPS122561, IPS107023, IPS85919 and 142 IPS106909). All actinopterygian specimens underwent chemical and mechanical 143 preparation. The chemical preparation included swabbing the pieces with formic acid 144 (5%) and mechanically removing the matrix surrounding or covering the skeleton using 145 a thin needle under a stereomicroscope. The specimens were imaged by using a 146 binocular Leica MZ 16A and line drawings were made with Corel Draw© software. 147 Repositories and institutional abbreviations.— All specimens examined in this study 148 are deposited in the: Institut Català de Paleontologia Miquel Crusafont (Sabadell, Spain) 149 and are labelled using the acronym IPS. 150 151 Systematic Paleontology 6 152 153 Subclass Actinopterygii Cope, 1887 154 Order Peltopleuriformes Gardiner, 1967 155 Family Peltopleuridae Brough, 1939 156 157 Genus Peltopleurus Kner, 1866 158 159 Figures 3-9 160 161 Peltopleurus cf. P. nuptialis 162 163 Type species.— Peltopleurus splendens Kner, 1866. Its type locality is Raibl, Carinthia 164 which is in a Julian marine limestone in Italy 165 166 Occurrence.— Lower levels of organic-rich laminated mudstones from the facies 167 association 1 (organic-rich laminated silty mudstone). Laminated Limestone and/or 168 Dolomites Unit of Calvet et al. (1993). 169 170 Description.— General morphology. Peltopleurus cf. P. nuptialis has a fusiform body 171 with a forked caudal fin and presents general features that all the species of Peltopleurus 172 share (see below). This taxon has two distinct morphotypes (herein named as 173 morphotype A and B, respectively) with differences in the pectoral, pelvic, anal, and 174 dorsal fins and in the rostral bone. Its maximum standard length is 25 mm, with a total 175 length of 29 mm and a head length constituting around 34% of the standard length. 176 7 177 Snout.— The rostral bone has a rounded convex shape with differences 178 representing two morphotypes. In morphotype A, this bone presents a smoothed 179 surface, whereas morphotype B specimens show at least two prominent conical 180 tubercles with a maximum height of 0.3 mm (Figs. 3.1 – 3.2 and 4). The nasal bone has 181 a convex shape with a small notch for the anterior nostril on its anterior margin (Figs. 182 3.3 and 4). It contacts the rostral bone. These two elements are in contact with the 183 frontal, the premaxilla, and possibly with the antorbital. However, this character cannot 184 be discern with confidence in any recovered specimen. The premaxilla is rectangular, 185 bearing two big conical teeth on its oral margin (Figs. 3.2 and 4). 186 Skull roof.— The frontal bone is broad and expanded in its posterior part and 187 narrower anteriorly. The surface of the frontal bone has at least 16 small conical 188 tubercles randomly arranged (Figs. 4 and 5). The parietal bone has a smooth surface and 189 its contact with the frontal bone is straight (Figs. 4 and 5). There is a ridge parallel to 190 the orbital margin of the frontal and parietal bones identified as the supraorbital sensory 191 canal. The subrectangular dermopterotic (Fig. 3.1) is placed in contact to the frontal, 192 parietal, the extrascapular and the suborbital (Figs. 3 and 4). The extrascapular and the 193 post-temporal are not well preserved due to the disarticulation of the skulls. 194 Circumorbital series.— There are two infraorbitals (Figs. 3 and 4). The first 195 infraorbital is in contact with the antorbital, the premaxilla, and the distal part of the 196 maxilla whereas the second infraorbital is the largest one, being in contact with the rest 197 of the maxilla and half of the preoperculum. The dermosphenotic is similar in size to the 198 first infraorbital, being in contact with the second infraorbital, the rest of the 199 preoperculum and the suborbital, the frontal and one supraorbital. No dermohyal is 200 observed due to preservational reasons. The supraorbitals are not well preserved in any 8 201 recovered specimens due to the state of preservation. However, in one specimen (Fig. 202 3.1) it is possible to discern a potential supraorbital. 203 Cheek bones.— The suborbital is large and triangular with rounded edges and 204 contacts the preoperculum, the operculum, the dermopterotic and the skull roof bones 205 (Figs. 3 and 4). 206 The preoperculum is trapezoidal with its upper and lower margins narrower than 207 the central portion. Its anterior margin is in contact with the infraorbitals 2 and 3. Its 208 posterior margin is in contact mainly with the operculum but also with the 209 suboperculum. On its lower margin, the preoperculum is in contact with the maxilla and 210 its upper margin is in contact with the suborbital (Figs. 3 and 4). The posterior margin 211 shows a ridge parallel to the margin identified as the preoperculum sensory canal. 212 The maxilla shows a thin anterior part and a broad rounded posterior one. The oral 213 margin bears at least 14 sharp conical teeth of different heights (Figs. 3 and 4). The 214 anterior margin is in contact with the premaxilla and the posterior part of the maxilla is 215 in contact with the preoperculum and the cleithrum. The palatal bones bear several rows 216 of flattened oval teeth hinting at a semi-durophagous diet (Fig. 7.3). 217 Opercular series.— The operculum and the suboperculum bones are D-shaped. 218 The operculum is large and in contact with the preoperculum and the suborbital on its 219 anterior margin and the cleithrum on its posterior margin (Fig. 3 and 4). The 220 suboperculum has a straight contact with the operculum. This suboperculum is 221 significantly smaller and in contact with the maxilla on its anterior margin. 222 Lower Jaw.— The dentary bone shows a narrow anterior portion and an expanded 223 posterior end, with at least one small notch on its middle part (Figs. 3.3 and 4). The oral 224 margin bears at least 16 sharp conical teeth of different height, slightly larger than those 225 of the maxilla. 9 226 Girdles and paired fins.— The shoulder girdle is composed by a robust cleithrum. 227 It is sickle-shaped, with an irregular surface, and a shorter supracleithrum (Figs. 3 and 228 4). The cleithrum is in contact with the posterior margin of the operculum and 229 suboperculum (Figs. 3.1 and 4). The branchiostegal rays are not preserved in any 230 specimen due to the fragility of these bones and the poor preservation of this area of the 231 skull. 232 The pectoral fin is long and made of at least seven distally segmented rays. On the 233 specimens referred to morphotype B these rays consist of a long proximal segment and 234 at least seven shorter segments (Figs 6 and 7.1). The unsegmented anterior ray bears six 235 sharp hooks on its anterior margin, followed by the first segmented ray showing at least 236 7 hooks along its anterior margin. The rest of these segmented rays show a single hook 237 on the distal margin. Specimens referred to morphotype A present a shorter fin, with the 238 same structure but without hooks. The pelvic fin is smaller than the pectoral fin, 239 composed by at least 8 rays and showing the same structure of rays and hooks as on the 240 pectoral fin (Fig. 6). 241 Median fins.— The dorsal fin is made of long lepidotrichia, composed of at least 242 10 distally segmented rays and four basal fulcra (Fig. 7.2). On morphotype B, the 243 segments from the anterior ray show a sharp hook on each fragment whereas in 244 morphotype A these rays are shorter and without any hook. 245 The anal fin shows two different patterns. In morphotype B, this anal fin is made 246 of at least eight rays with a minimum of five segments bearing hooks. Above these rays 247 there are an indeterminate number of very thin rays ending in small sharp hooks. This 248 fin is partially covered by a triangular scute (Fig. 8). In morphotype A, this anal fin is 249 formed of at least 14 rays with a minimum of five segments missing the hooks and the 250 scute. 10 251 The caudal fin is hemiheterocercal with a forked profile and composed of 24 252 principal rays made up of a minimum of 8 segments (Figs. 6 and 9). There are four 253 basal fulcra on each lobe and four or five epaxial rays on the upper lobe. However, the 254 state of preservation precludes to distinguish more details of the caudal fin as the 255 fringing fulcra and procurrent rays. 256 Squamation.— The scale covering is made up of 35 or 36 vertical smooth scales 257 rows along the lateral line of the body (Figs. 6 and 9). The lateral-line scales are 258 sigmoidal and increase in depth on the anterior part of the body and decrease in size to 259 the posterior part. There are two rows of rectangular scales on the dorsal margin above 260 the lateral-line scales and one row on the ventral margin below the lateral line scales 261 (Fig. 9). All the scales have a small spine on the posterior margin (Fig. 9). The caudal 262 region is made up of five triangular scale rows. 263 264 Material.— IPS106977, anterior part of the body. IPS106957, a complete body missing 265 the anterior part of the skull. IPS107023, a poorly preserved body including the skull. 266 IPS86048, a nearly complete body with its disarticulated skull and all the fins. 267 IPS85811, a partially disarticulated body showing some cranial features. IPS106902, a 268 partially disarticulated body with a good preservation of some fin 269 characters. IPS122561, anterior part of the body preserving most of cranial bones. 270 IPS85919, a partially disarticulated body showing some features of the fins. IPS106909, 271 a poorly preserved body showing some cranial features. 272 273 Remarks.— The small size of the body, the presence of a big operculum, a tall 274 preoperculum and a hemiheterocercal caudal fin are diagnostic characters of 275 Peltopleuriformes (Gardiner, 1967). Recently, Xu and Ma (2016) defined 11 276 Peltopleuriformes sensu stricto including only Peltopleuridae and Thoracopteridae. The 277 monophyly of these clades, based on Xu and Ma (2016) analyses, is well supported by 278 five synapomorphies: supraorbital sensory canal ending in the frontal; absence of a 279 preoperculum/dermopterotic contact; presence of a postpiracle; presence of dense 280 brush-like rays articulating proximally with several stout segments in the male anal fin; 281 and presence of enlarged lateral scutes associated with the anal fins. All these characters 282 are identified on the Odèn specimens, except the presence of postpiracle, not observed 283 probably by preservation reasons. 284 Regarding Peltopleuridae, the original diagnosis of this group provided by Brough 285 (1939) include as diagnostic characters the small size of the body, large orbits, fins of 286 small to moderate size, hemiheterocercal forked tail, deep flank scales, frontals large 287 and elongated, rectangular parietals, long and narrow supratemporals, wide 288 preoperculum attached to the maxilla, large operculum, small suboperculum, and few 289 branchiostegal rays. All these characters are identified on the Odèn specimens with the 290 exception of the branchiostegal rays, which are not preserved. Brough (1939) marked as 291 a diagnostic character a weak dentition with minute teeth on the maxilla, or no teeth at 292 all. However, Lombardo (1999) noted that this character is not really diagnostic for 293 Peltopleuridae due to the strong dentition present in Peltopleurus notocephalus and 294 Peltopleurus nuptialis (Bürgin, 1992; Lombardo, 1999). For this reason, Lombardo 295 (1999) questioned the diagnosis of Brough (1939), although she did not present an 296 emended diagnosis of this family. 297 Peltopleurus is a genus included within the clade Peltopleuridae, including 12 298 species, from Middle to Upper Triassic. This genus have been recovered from Austria, 299 Italy, Spain, Switzerland and South China (Kner, 1866; Brought, 1939; Beltan, 1972, 300 1975; Bürgin, 1992; Lombardo, 1999; Cartanyà, 1999; Xu and Ma, 2016; Xu et al., 12 301 2018). It was erected on the basis of a unique combination of characters (Kner, 1866): i) 302 a small fish with a fusiform body, in agreement with the Odèn specimens with an 303 average ratio of total length - maximum body depth of 3.89; ii) a flank with a 304 longitudinal row of tall scales; the specimens from Odèn show that longitudinal row of 305 deep scales; iii) a vertical preoperculum and a maxilla with a narrow anterior region and 306 an expanded postorbital; this vertical preoperculum and this narrow morphology on its 307 anterior part and expanded on its posterior part maxilla are also present on the 308 specimens from Odèn; iv) the presence of a wide and semicircular opercular region; the 309 opercular region in the specimens from Odèn is broad and D-shaped, matching with the 310 description for this genus; v) caudal fin externally symmetrical, as present on the Odèn 311 specimens. vi) a short axial body lobe with at least six epaxial rays. On the specimens 312 reported here, the axial body is short and there are at least four or five epaxial rays. All 313 aforementioned characters support the attribution of reported specimens from the Odèn 314 site to the genus Peltopleurus. 315 Differences on the pectoral, pelvic, anal and dorsal fins as well on the rostral bone 316 reveals the presence of dimorphism in the Odèn taxon. Morphotype A has a pectoral fin 317 made of at least seven rays distally segmented, a pelvic fin with at least eight rays 318 distally segmented, an anal fin composed by at least 14 rays distally segmented, a dorsal 319 fin composed by at least 10 rays distally segmented, and the rostral bone being rounded 320 and smoothed. Morphotype B has a pectoral fin made of at least seven rays distally 321 segmented and much longer than those of morphotype A; moreover, morphotype B 322 presents the following characters: the anterior unsegmented ray bears on its anterior 323 margin six sharp hooks, followed by the first segmented ray bearing at least seven 324 hooks along its anterior margin. The rest of these segmented rays show: a single hook 325 on its distal margin; a pelvic fin with at least eight rays distally segmented with the 13 326 same hook structure as the pectoral fin and an anal fin made of at least eight rays 327 composed by a minimum of five segments bearing hooks. Above these rays there is an 328 indeterminate number of very thin rays ending in small sharp hooks. This fin is partially 329 covered by a triangular scute. The dorsal fin is composed of at least 10 rays distally 330 segmented, the segments from the anterior ray show a sharp hook on each fragment and 331 the rostral bone is rounded and it has a prominent tubercle. 332 The presence of two morphotypes with differences mainly related to fin 333 morphology is know from Peltopleurus species such as P. nuptialis, where what would 334 correspond to our morphotype A is assumed to be a female and morphotype B would 335 represent the male as shown by the presence of hook structures as discussed in 336 Lombardo (1999). 337 The specimens herein described present similarities with the specimens referred by 338 Lombardo (1999) to Peltopleurus nuptialis, erected on basis to the following combination 339 of features. Small species of Peltopleurus, up to 25 mm standard length with 32 vertical 340 scale rows. Our specimens share this standard length but with 35 or 36 scale rows. Two 341 scales rows dorsal to the deepened flank scales and one ventral. The specimens recovered 342 in the Pyrenees show the same squamation pattern. Posterior margin of all scales with one 343 to three small spines. The specimens herein described show only one spine on the 344 posterior margin of all scales. All fins, except for the caudal one, have anterior margins 345 bearing a series of hook-like structures. These hook structures are identified in our 346 specimens on all the fins except the caudal one. There is distinct sexual dimorphism. 347 Despite the similarities between P. nuptialis and the specimens herein described 348 shown on the diagnosis, some differences are worth highlighting. The pectoral fin in the 349 Odèn specimens seems to be significantly longer than the pectoral fin on P. nuptialis. 350 The frontal bones in the specimens from Odèn have at least 16 small conical tubercles 14 351 randomly arranged, feature not identified on P. nuptialis. The cleithrum on the Odèn 352 specimens seems to be longer than that described in P. nuptialis. Considering the state 353 of preservation of the specimens described herein, we decided to keep a conservative 354 taxonomic assignation and, although subtle differences with P. nuptialis exist, we prefer 355 to assign these specimens to Peltopleurus cf. P. nuptialis. Some characters are not well 356 preserved in the Odèn specimens and additional data are required to assess with 357 confidence the taxonomical assignment of this material. 358 359 Results 360 Summary of macrofaunal assemblages at Odèn locality.— The first fossil recovered 361 from Odèn consisted of postcranial remains referred to Saurichthys sp. by Lehman 362 (1964). Calzada and Magrans (1997) reported a lingulate brachiopod. A second 363 specimen of Saurichthys, a lower jaw, was described by Cartanyà et al. (2011). Finally, 364 a skull of the large-bodied colobodontid Colobodus giganteus was also recovered and 365 described in detail by Cartanyà et al. (2015). 366 More than 90% of the body fossils recovered during last field campaigns (see 367 Methods for further details) belong to vertebrates and only about 10 invertebrate 368 specimens are referred to the bivalve Pseudocorbula gregaria (Fig. 10.1); among the 369 vertebrate fossils, almost 60% belong to Peltopleurus, around 15% belong to 370 indeterminate actinopterygians (Fig. 10.3), and 20 specimens are referred to Saurichthys 371 (representing almost 10% of the total samples, mostly representing lower jaws and, to a 372 lesser extent, cranial bones). Around 20 specimens (representing almost 10% of the total 373 samples) have been tentatively referred to an undetermined halecomorph actinopterygian; 374 furthermore, few additional poorly preserved colobodontid remains have been also 15 375 discovered. Furthermore, there are 10 ribs and teeth tentatively referred to sauropterygian 376 reptiles (Fig. 10.2). 377 378 Facies description .—Three facies associations were identified based on depositional 379 texture, skeletal and non-skeletal components, sedimentary features, and lateral 380 relationships (Figs. 11, 12 and 13). The recognition of facies heterogeneities across the 381 studied area enabled the identification of the sedimentary environments. 382 383 Facies association 1: Organic-rich laminated silty mudstone.—This facies consists 384 of an up to 11.5 m thick, laterally restricted alternation of 30- to 80- cm-thick dark grey 385 to pale brown, fetid and organic-rich finely laminated silty mudstones with up to 2-m- 386 thick massive and organic-rich mudstone (Fig. 11.1 - 11.2). Most massive layers show 387 planar to slightly undulated bottom contacts. Rare intervals exhibit channel-fill 388 structures with fining-upward cross-bedded bundles over erosional, sharp bases (Fig. 389 11.1). In places, up-to-10-cm-thick intraclastic packstone, or up to 40 cm-thick brown 390 marly clay intervals are interbedded within the finely laminated units. Some metric- 391 scale slumped and fractured beds are recognized in the massive intervals. The major 392 allochems are carbonaceous intraclasts (up to 1 mm wide), plant remains (up to 1 cm 393 wide), fish coprolites (up to 1 cm wide), fish scales, peloids, thin-shelled bivalve 394 intraclasts, and unidentified microfossil remains (Fig. 11.3 - 11.4). Trace fossils are 395 absent, but the organic-rich mudstone component of this facies yielded a fish 396 assemblage comprising at least four taxa (see below), scarce tetrapod remains assigned 397 to marine reptiles (sauropterygians), bivalves (Pseudocorbula gregaria), and 398 brachiopods (Lingula sp.). Most actinopterygians referred to Peltopleurus were found in 399 the laminated lower levels, whereas the halecomorph specimens were recovered from 16 400 the upper horizons. In contrast, Saurichthys specimens were regularly found throughout 401 the entire facies (Fig. 14). 402 The thin lamination, absence of bioturbation, good preservation of the 403 actinopterygian remains (retaining organic matter and remaining articulated), and 404 scarcity of in-situ benthonic fossils suggest anoxic/dysoxic conditions. 405 The depositional texture and sedimentary features of facies association 1 suggest 406 deposition below the fair-weather wave base under relatively low-energy conditions in 407 shallow subtidal marine environments episodically sourced by silt and clay. However, 408 the presence of Pseudocorbula gregaria might indicate the proliferation of such 409 bivalves during periods of limited terrigenous input (García-Gil, 1991). The thinly 410 bedded organic-rich and undisturbed mudstone laminae suggest both low-energy 411 environments and recurrent oxygen deficiency at the sea bottom leading to anoxic to 412 suboxic conditions that probably enhanced fossil fauna preservation. The diversity of 413 vertebrate fauna encountered in this facies association suggests enough water depth to 414 support nektonic lifestyles. Channel-fill structures over erosional bases suggest the 415 circulation of sporadic sea-bottom currents (Fig. 14). 416 417 Facies association 2: Laminated silty mudstone to wackestone .—Facies association 418 2 is made up of 8 m thick, laterally continuous (up to 400 m wide) thinly bedded 419 alternation of centimeter-thick silty pale grey mudstone to wackestone with millimeter- 420 thick dark brown-grey silt to clay laminae (Fig. 12). The tops of the limestone-rich 421 intervals exhibit persistent wave ripple structures with straight, symmetrical, and 422 parallel crests (Fig. 12.1). Ripple marks range between 0.5 to 1 cm in length, and 423 normally are 0.5 cm in height. Inter-ripple depressions are silt-rich and in many cases 424 dewatering structures occur (Fig. 12.2 – 12.4). Flame structures tend to leave open 17 425 porosity conduits at 45º to 80º from ripple planes, which are partially filled by silt or 426 cement (Fig. 12.3 – 12.4). Convolute lamination is observed as slightly folded and 427 unbroken layers (up to 15cm in height) with arcuate crests (Fig 12.2) laterally extending 428 over 20 to 100 cm in outcrop. The siliciclastic proportion of this facies is slightly 429 increased towards the eastern section of the outcrops where dewatering structures are 430 growingly less evident. 431 The depositional texture and lateral stratigraphic distribution of this unit suggest 432 sedimentation in shallow subtidal to intertidal mud flats with variable contributions of 433 silt and clay in a coastal environment. The low frequency of the ripple bedforms and 434 their elongated, parallel crests suggest low to moderate hydraulic conditions in wave- 435 influenced settings. 436 437 Facies association 3: Slumped and collapsed breccia deposits .—This facies 438 association consists of between 2-to-8-m-thick laterally restricted unit of slumped and 439 contorted beds dominated by poorly sorted, mainly clast-supported breccia and blocks 440 (5 to 60 cm in diameter) (Fig. 13). This unit is pinching out towards the eastern part of 441 the outcrop. Most of the blocks are made up of sub-consolidated silty mudstone to 442 wackestone (Facies Association 2) and, to a lesser extent, of reworked organic-rich 443 laminated silty mudstone (Facies Association 1) (Fig. 13.1 – 13.2). The former is more 444 abundant towards the western area of the outcrop. 445 According to the depositional texture and the stratigraphic relationships, this 446 facies is interpreted as a restricted gravitational collapse formed by remobilization of the 447 shallower facies association 2 on top of the deeper facies association 1. The lateral 448 thickness variations of facies association 3 suggest rising water depths westwards with 449 an increase in deposition of reworked and contorted laminated silty mudstones towards 18 450 such direction. Gravity-flow deposition could be triggered by storm events or 451 syntectonic activity as identified in adjacent coeval Middle Triassic areas of the Catalan 452 Basin (Mercedes-Martín and Buatois, 2021). 453 454 Discussion 455 456 Faunal assemblage. —The macrofaunal assemblage recovered at the Odèn site includes 457 two invertebrate taxa: a lingulate brachiopod and the bivalve Pseudocorbula gregaria. 458 Aside from being less diverse, invertebrates are in appearance volumetrically less 459 abundant in comparison with the fish assemblage present. In this assemblage, the genus 460 Peltopleurus is highly dominant. Less common taxa are represented by the 461 colobodontid Colobodus giganteus, the long-snouted Saurichthys, and an indeterminate 462 halecomorph. Specimens of Saurichthys can only be identified at the genus level, in 463 agreement with previous reports by Lehman (1964), Cartanyà et al. (2011) and Fortuny 464 et al. (2011). 465 The Odèn fish assemblage is comparable to that found at the coeval locality of 466 Vilanova de la Sal (Fig. 1). This site is particularly known for the presence of a semi- 467 articulated specimen of a pachypleurosaur sauropterygian (Fortuny et al., 2011), as well 468 as some fragmentary actinopterygian fossils including Peltopleurus and Saurichthys that 469 have never been described in detail. Furthermore, the site yielded specimens tentatively 470 attributed to the genus Eosemionotus (Fortuny et al., 2011), a taxon unknown so far 471 from the Odèn site. Colobodus, halecomorphs, and invertebrates are apparently absent 472 in the Vilanova de la Sal outcrops, although the site has been less extensively sampled. 473 Additional taxonomic and sedimentological work, as well as a more extensive sampling 474 at Vilanova de la Sal site and coeval locations in the neighboring sub-basins are 19 475 required to better reconstruct the Pyrenean paleoecosystems during the Middle-Late 476 Triassic transition. 477 Although the fossil-bearing sites at Mora d’Ebre-Camposines and Mont-ral- 478 Alcover are roughly coeval with the Pyrenean Odèn site (as all of them are situated in 479 Upper Muschelkalk facies), they are characterized by different faunal assemblages. For 480 example, the Mora d’Ebre-Camposines site displays an important assemblage of 481 invertebrates, particularly ammonoids (including Protachyceras hispanicum, 482 Protachyceras vilanovae, Anolcites sp. and Iberites pradoi), thylacocephalans, and 483 bivalves (dominated by Daonella) (Cartanyà et al., 2019), none of which have been 484 recovered at Odèn. This is consistent with the particular geological context of the Odèn 485 site, located adjacent to more restricted coastal mud flats compared to Mora d’Ebre- 486 Camposines that were likely situated in more open marine settings. In addition, the 487 Ladinian vertebrate fauna in Mora d’Ebre-Camposines is dominated by the perleidid 488 actinopterygian Moradebrichtys vilasecae, although Saurichtys is also present. Overall, 489 the faunas and environments at Mora d’Ebre-Camposines and Odèn are clearly different 490 and might correspond to slightly different ages with the Odèn outcrops potentially 491 slightly younger. 492 On the other hand, Mont-ral – Alcover record a greater number of invertebrate 493 and vertebrate specimens. Nektonic and planktonic organisms are dominated by 494 actinopterygians, sauropterygian reptiles, cephalopods, and swimming decapods, among 495 others. Benthic forms like reptant decapods, crinoids, limulids, holothurids, and 496 brachiopods are present but not dominant (Via-Boada et al., 1977). Up to 13 families of 497 actinopterygians are recorded in the Mont-ral – Alcover outcrops. Of particular interest, 498 saurichthyids are abundant, including Saurichthys. However, Peltopleurus, 499 Eosemionotus, Perleidus and Colobodus, are also present (Cartanyà, 1999). 20 500 Differences in faunal diversity between the Mont-ral –Alcover and Odèn sites are 501 striking despite the fact that some taxa (e.g. Peltopleurus, Saurichthys, Colobodus and 502 marine reptiles) can be found in both assemblages. We acknowledge that taphonomic 503 and sampling bias possibly exists, and future surveys will help to get a clearer picture of 504 the faunal composition in these settings. Despite the Catalan Coastal Ranges sub-basin 505 (Mont-ral –Alcover sites) and the Pyrenean sub-basin (Odèn site) recorded peritidal to 506 subtidal marine deposition during the Middle Triassic times, more work is required to 507 further reconstruct the paleogeography and the degree of connectivity between both 508 sub-basins during the Ladinian-Carnian. 509 510 Chronostratigraphical implications. —The age of the Odèn fossiliferous levels is 511 difficult to constrain, but potentially ranges from the ?late Ladinian to the early - middle 512 Carnian. The possible oldest age (?late Ladinian) can be assumed based on the presence 513 of the actinopterygian genus Peltopleurus, which is also recovered from the late 514 Ladinian of Montral-Alcover (Cartanyà, 1999). Indeed, lateral equivalent carbonate 515 units have a late Ladinian – early Carnian age based on palynomorph associations (see 516 García-Ávila et al., 2020). Nonetheless, it should be noted that Peltopleurus is also 517 known from even older stratigraphic intervals (Anisian and Ladinian) at Monte San 518 Giorgio (Lombardo, 1999; Furrer et al., 2008). Thus, a greater age cannot be completely 519 ruled out based only on the presence of the actinopterygian Peltopleurus. 520 On the other hand, the palynological assemblage identified in the Laminated 521 Limestone and/or Dolomites Unit in Odèn has been dated to the middle Carnian (Calvet 522 et al., 1993). 523 21 524 Paleonvironmental and paleogeographic implications.—The Upper Muschelkalk 525 carbonate sedimentation in the Triassic Catalan Basin (NW Spain) probably took place 526 in extensive fault-block marine carbonate ramp settings during periods of rapid syn-rift 527 subsidence (Calvet and Tucker, 1988, Mercedes-Martin et al., 2013). However, the 528 sedimentological and paleogeographical setting of the co-eval deposits in the South 529 Pyrenean basin (NE Spain) is less well resolved (Calvet et al., 1993). 530 The present work refines the sedimentary and paleoenvironmental context of the 531 Upper Muschelkalk to Keuper facies transition outcropping at Odèn (Fig. 14). The 532 study of lateral and vertical facies relationships has permitted the recognition of two 533 types of sedimentary environments, from laterally extensive shallow subtidal-intertidal 534 coastal mud flats to more restricted and deeper subtidal settings. The occurrence of 535 gravity flow deposits (facies association 2) and syn-sedimentary slumped and contorted 536 beds in facies association 1 suggest active fault-block instability likely involved in 537 facies differentiation. The slightly steeped paleoslope toward the west is thought to 538 segregate the shallower coastal silty mud flat areas and the deeper subtidal and low 539 energy settings, where abundant vertebrate faunas proliferated. Rapid lateral facies shift 540 suggests a strong degree of basin compartmentalization in the Pyrenean sector when 541 compared with the time-equivalent facies in settings of the Coastal Catalan Ranges 542 (e.g., Gaia or Priorat domain, Mercedes-Martín et al., 2013). In the former settings, 543 sedimentary architectures of kilometer scale have been recognized with more gradual 544 facies lateral changes. Despite such differences, the tectonic compartmentalization of 545 these marine basins is thought to have favored the preferred development of taphonomic 546 traps in subtidal settings where enhanced faunal preservation occurred. 547 The predominance of silty and clay-rich carbonate facies in the Odèn outcrops 548 contrasts with the conspicuous absence of terrigenous sediment portions in the Triassic 22 549 Coastal Catalan Ranges. This suggest that the region of Odèn represents land attached 550 setting where shallow subtidal- intertidal carbonate coastal deposition was influenced 551 by silt/ clay sources, while in the Coastal Catalan Ranges more open marine conditions 552 prevailed. 553 554 Conclusions 555 556 Recent paleontological surveys in the Upper Muschelkalk to Keuper deposits at Odèn 557 (Pyrenean basin) have provided new faunal data suggesting that this location can hold 558 the key to better clarify the poorly known local ecosystem composition and shed light 559 on the diversification among peltopleuriform actinopterygians during the Middle 560 Triassic. 561 To date, the faunal assemblage includes, at least, four actinopterygian taxa: 562 Peltopleurus cf. P. nuptialis; Sauricthys sp.; Colobodus giganteus, and an indeterminate 563 halecomorph. A few disarticulated remains document the presence of sauropterygian 564 reptiles (Fig. 14). 565 The age range of the organic-rich laminated silty mudstone fossil-bearing units is 566 considered to be ?late Ladinian – middle Carnian based on palynomorph associations 567 (Calvet et al., 1993). The depositional environments where the faunas existed suggest 568 sedimentation in shallow subtidal, low-energy coastal settings, below the fair-weather 569 wave base and sourced by sporadic silt/ clay. Deposition in organic-rich laminated silty 570 mudstone intervals might have led to preservation of the vertebrate remains under 571 anoxic conditions. The tectonically driven compartmentalization of these marine basins 572 played a key role favoring subtidal settings as taphonomic traps for enhanced faunal 573 preservation in the studied site and likely in other locations of Tethys domain. Despite 23 574 the fact that the Catalan Coastal Ranges sub-basin (Mont-ral –Alcover sites) and the 575 Pyrenean sub-basin (Odèn site) were dominated by peritidal to subtidal sedimentation 576 during Middle Triassic times, more work is warranted to further reconstruct the 577 paleogeography and the degree of connectivity between these sub-basins and the Tethys 578 sea during the Ladinian-Carnian interval. 579 580 Acknowledgements 581 Special thanks to E. Solà, A. Sagarra, A. G. Sellès, M. Petruzzelli, E. Mujal, M. Vilalta, 582 A. Lecuona, M. Fernàndez-Coll, B. Vila, À. Galobart and J. Marmi for fieldwork 583 support. J. Gallemí and S. Calzada (Barcelona, Catalonia) are acknowledged for their 584 contribution on relevant information about the site. I. Casanovas-Vilar (ICP) is 585 acknowledged for imaging support. The authors acknowledge the logistic support of the 586 Odèn town council and “Centre de Natura d’Odèn”. J.F. is a member of the 587 consolidated research group (GRC) 2017 SGR 86. A.B. is supported by a Juan de la 588 Cierva Incorporación Fellowship (IJC2018-037685-I, funded by Ministerio de Ciencia e 589 Innovación of the Spanish Government). We acknowledge support from the CERCA 590 programme (ICP) from the Generalitat de Catalunya, and the projects “Vertebrats del 591 Permià i el Triàsic de Catalunya i el seu context geologic” (Ref 2010/70085), “Evolució 592 dels ecosistemes amb faunes de vertebrats del Permià i el Triàsic de Catalunya” (ref. 593 2014/100606) and “Evolució dels ecosistemes durant la transició Paleozoic–Mesozoic a 594 Catalunya” (ref. CLT009/18/00066), based at the ICP and financially supported by the 595 Departament de Cultura (Generalitat de Catalunya). R.M.M. acknowledges the Linnean 596 Society of London for supporting this work throughout a Percy Sladen Memorial Fund 597 Grant. An anonymous reviewer and the editor (H.-D. 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Nearly complete skulls with a drawing of the 762 identified bones, the doted lines represent sensory canals. (1) IPS106977. (2) 763 IPS122561. (3) IPS107023. Cl, cleithrum; Den, dentary bone; Dpt, dermopterotic; Dsp, 764 dermosphenotic; Exsc, extrascapular; Fr, frontal; Io, infraorbital; Mx, maxilla; Na, 765 nasal; Op, operculum; Pa, parietal; Par, Parasphenoid; pf, pectoral fin; Pmx, premaxilla; 766 Pop, preoperculum; Pt, posttemporal; Ro, rostral; Scl, supracleithrum; So, suborbital; 767 Sop, suboperculum; Su, supraorbital. 768 33 769 770 Figure 4. Peltopleurus cf. P. nuptialis. Idealized reconstruction of the skull based on 771 the combined observations of the specimens studied. Ao, antorbital; Cl, cleithrum; Dhy, 772 dermohyal; Dpt, dermopterotic; Dsp, dermosphenotic; Exsc, extrascapular; Fr, frontal; 773 Io, infraorbital; Lj, lower jaw; Mx, maxilla; Na, nasal; Op, operculum; Pa, parietal; 774 Pmx, premaxilla; Pop, preoperculum; Pt, posttemporal; Ro, rostral; Scl, supracleithrum; 775 So, suborbital; Sop, suboperculum; Su, supraorbital. 776 777 34 778 Figure 5. Peltopleurus cf. P. nuptialis. Skull roof of the specimen IPS85811 showing 779 the small conical tubercles randomly arranged on the frontal bone (black dots) and the 780 supraorbital sensory canal (dotted lines). (1) Photograph. (2) Interpretative drawing. Fr, 781 frontal; Pa, parietal. 782 783 Figure 6. Peltopleurus cf. P. nuptialis. IPS86048, a nearly complete body with its skull 784 disarticulated. (1) Photograph. (2) Interpretative drawing. In this morphotype B 785 specimen it is possible to identify the long dorsal and pectoral fins with their hooks, the 786 pelvic fins with its hooks, the anal fin partially covered by the scute and the caudal fin. 787 35 788 789 Figure 7. Peltopleurus cf. P. nuptialis. (1) IPS86048 and (2) IPS85919., detail of the 790 long pectoral and dorsal fins with their hook structure on the anterior margin of the 791 segments. (3) IPS106909, detail of the skull showing the lines of flattened oval teeth. 792 793 794 Figure 8. Peltopleurus cf. P. nuptialis. Morphotype B anal fins showing the described 795 structure composed by normal rays (NR) bearing hooks on each segment, a series of 796 thin rays (ThR) ending in small sharp hooks (Hs) and a triangular scute (Sc) covering 797 the fin. (1) IPS86048. (2) IPS106957. (3) IPS106902. 798 799 36 800 Figure 9. Peltopleurus cf. P. nuptialis. IPS106957, a nearly complete body missing the 801 anterior portion. This morphotype B specimen shows the main features of the 802 squamation. (1) Photograph. (2) Interpretative drawing. 803 804 805 Figure 10. Additional faunas recovered from the studied section. (1) Pseudocorbula 806 gregaria (IPS123389). (2) Sauropterygian rib (IPS-86018). (3) small robust dentary 807 from an unidentified actinopterygian (IPS122539). 808 809 37 810 811 Figure 11. Organic-rich laminated silty mudstone (Facies association 1). (1) Massive 812 tabular beds showing channel-fill with cross-bedded bundles over erosional surfaces. (2) 813 Massive beds alternate with finely laminated, fossil-bearing mudstones (top). (3) 814 Actinopterygian remains in the top laminae of the finely laminated facies. (4) 815 Photomicrograph of organic-rich micritic mudstone with floral remains (arrows). 816 38 817 818 Figure 12. Laminated silty mudstone to wackestone (Facies association 2). (1) 819 Laminated mudstone to wackestone units showing wave ripple structures with straight, 820 symmetrical, and parallel crests. Note silt-rich intervals in pale brown color. (2) 821 Dewatering structures tend to form open conduits producing vertically folded structures. 822 (3) Waterscape conduits can be at 45º to 80º from ripple planes (arrows) which are 823 partially filled by silt or cement. (4) Photomicrograph of dewatering flame structures 824 filled by calcite cement. 825 39 826 827 Figure 13. Slumped and contorted breccia deposits (Facies association 3). (1) Detail of 828 slumped organic-rich laminated facies (Facies association 1, F1), (2) In some settings, 829 slumped and collapsed beds are dominated by poorly sorted, mostly clast-supported 830 breccia and blocks of Facies association 2 (F2). 831 40 832 833 Figure 14. Schematic paleoenvironmental reconstruction of Facies Association 1 (FA1) 834 which contains the macrofauna studied in this work. 41