Cretaceous Research 131 (2022) 105094 Contents lists available at ScienceDirect Cretaceous Research journal homepage: www.elsevier.com/locate/CretRes Identification of a large anguimorph lizard (Reptilia, Squamata) by an articulated hindlimb from the upper Maastrichtian (Upper Cretaceous) of Basturs-1 (Lleida, Spain) ndez a, *, A. Bolet b, c, A. Torices d, A. Pe A. Cabezuelo Herna rez-García a a Grupo de Biología Evolutiva, Facultad de Ciencias, UNED, Avda Esparta s/n, Las Rozas, Madrid, 28232, Spain b  de Paleontologia Miquel Crusafont, ICTA-ICP, Edifici Z, Calle de Les Columnes s/n, Campus UAB, Cerdanyola del Vall Institut Catala es, Barcelona, 08193 Spain c School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol, BS8 1RJ United Kingdom d Departamento de Ciencias Humanas, Universidad de La Rioja, Luis de Ulloa 2 Logron ~ o, La Rioja, 26004, Spain a r t i c l e i n f o a b s t r a c t Article history: Appendicular remains of squamate reptiles are barely described in the fossil record due to their low Received 29 March 2021 preservational potential and generally poor diagnostic information. Not many squamate fossil individuals Received in revised form preserve appendicular bony elements, these being mainly restricted to the rare articulated specimens 6 November 2021 found in a limited number of localities with specific conditions that favor exceptional preservation. Accepted in revised form 10 November 2021 Available online 17 November 2021 Detailed descriptions of these bones, especially tarsals and metatarsals, are thus scarce in the literature due to the lesser relevance given to these elements in most anatomical descriptions. In this study we analyze an unpublished fossil specimen from the Maastrichtian of Basturs-1 (Lleida, Catalonia, Spain) Keywords: Iberian Peninsula corresponding to several articulated appendicular pes bones of a possible member of Varaniformes. We Mesozoic also provide detailed insights on the anatomy of the tarsalia and metatarsalia, particularly in angui- Upper Cretaceous morphs. The fossil specimen here described, with an estimated snout-vent length (SVL) of ~581 mm, Varaniformes reveals the putative varaniform from Basturs-1 as one of the largest Mesozoic terrestrial lizards, and Metatarsal possibly the largest from the European fossil record. Previous observations of an association between large lizards and dinosaur nesting sites are further supported by the find of this giant form in a locality known for the presence of numerous dinosaur eggs. © 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 1. Introduction used to group them as well as related extinct taxa. Gao and Norell (1998) used the term in a more restrictive sense, consisting in the The squamate fossil record from the Maastrichtian (uppermost most recent common ancestor of Telmasaurus and Varanidae, and Cretaceous) of Europe includes representatives of Iguania, “Scin- all its descendants. Conrad (2008) and Conrad et al. (2011a) used comorpha”, Anguimorpha, Ophidia and Gekkota (Folie and Codrea, the term Varaniformes for the group containing forms closer to 2005; Pereda-Suberbiola, 2009; Bolet Mercadal, 2014; Bolet, 2017; Varanus than to Heloderma or mosasaurs. In contrast to Conrad Marmi et al., 2014; Csiki-Sava et al., 2015; Blanco et al., 2015, 2016; (2008), Conrad et al. (2011a) recovered “Varanoidea” as para- Ortega et al., 2015; Blanco, 2017). European Maastrichtian angui- phyletic in their combined evidence analysis of anguimorph re- morphs contain anguids (e.g. Blain et al., 2010), but most have been lationships, in agreement with molecular phylogenetic analyses referred to groups included in the old conception of “Varanoidea”. that consider Shinisaurus as more closely related to Varanus than In this view of squamates interrelationships, based on morpho- Heloderma. We here refer to Varaniformes sensu Conrad (2008), logical data (e.g. McDowell and Bogert, 1954; Pregill et al., 1986; and use the term “Varanoidea” informally for those fossils whose Caldwell, 1999; Conrad, 2008; Gauthier et al., 2012), helodermatids attribution was made under the old definition of the term, and are and varanids were closely related, and the term “Varanoidea” was too incomplete to support their attribution to either monstersaurs (Heloderma plus its stem) or varaniforms. All of this is further complicated by the uncertain position of mosasauriforms, which * Corresponding author. have been considered as “varanoids” (e.g. Estes et al., 1988; Conrad, ndez). E-mail address: alberto1996febrero@gmail.com (A. Cabezuelo Herna https://doi.org/10.1016/j.cretres.2021.105094 0195-6671/© 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). ndez, A. Bolet, A. Torices et al. A. Cabezuelo Herna Cretaceous Research 131 (2022) 105094 2008; Conrad et al., 2011a), pythonomorphs (a clade consisting in 2. Materials and methods mosasaurs plus snakes, see Lee, 1997; Lee and Caldwell, 2000 and Reeder et al., 2015), or recovered in a stem-ward position outside A total of 161 specimens belonging to both extinct and extant Anguimorpha (stem “scleroglossans” in Gauthier et al., 2012). Note, lepidosaurs were considered for the comparative study performed however, that mosasauriforms are only tangentially considered here. Some of the specimens corresponding to extant species were here, basically for discarding mosasauriform affinities of the fossil studied firsthand in the MACV, MNCN, and MNHN collections. The described, and for considering their distribution in the paleogeo- information for the other extant specimens considered here was graphic figures. Terrestrial “varanoids” have been reported from the obtained from the online platforms GBIF (Global Biodiversity In- Upper Cretaceous of Europe (e.g. Buffetaut et al., 1997; Laurent et formation Facility (https://www.gbif.org/)), iDigBio (Integrated al., 2002; Houssaye et al., 2013a; Rage, 2013; Ortega et al., 2015), Digitized Biocollections (https://www.idigbio.org/)) and the 3D although material is too fragmentary to provide an assignation to simulator MorphoSource (https://www.morphosource.org/). In- either monstersaurs or varaniforms. Iberian fossils referred to formation about fossil individuals was mainly obtained from the “varanoids” include taxa ranging from the Barremian or Aptian to papers in which those individuals were originally described (see the Maastrichtian, being mosasaurs (then considered to be “vara- Supplementary information 1 in Appendix A). noids”, but see above) the most abundant group (Bardet et al., 1999, Based on previous works (see Borsuk-Białynicka, 2018 and ref- 2006, 2013a,b; Pereda-Suberbiola et al., 2015) (Fig. 1). Regarding erences therein), the following measurements were obtained using Iberian terrestrial “varanoids”, they include Arcanosaurus ibericus previously defined criteria: hooking angle of the fifth metatarsal (vertebrae from the Barremian or Aptian of Salas de los Infantes, (ha), corresponding to the angle between the long axis of the Burgos) and some other indeterminate forms (vertebrae from the metatarsal and a line perpendicular to the articular facet for the upper Campanian or lower Maastrichtian of Lo Hueco, in Cuenca, fourth distal tarsal; lateral plantar tubercle angle (lpta), corre- and Aveiro and Viso, in Portugal; and upper Maastrichtian of sponding to the angle between this tubercle in relation to the Albaina, Trevin ~ o County) (Antunes and De Broin, 1988; Vullo et al., medial plantar tubercle and the outer process; inflexion angle (inf), 2009; Houssaye et al., 2013b; Ortega et al., 2015; Pereda-Suberbiola relating to the bending of the long axis in the plantar-dorsal plane; et al., 2015). angulation, considering the geometric shape of the fifth metatarsal Here we report a previously undescribed specimen attributable in proximal view; distal tarsal proportion (dtIV/dtIII), considering to Anguimorpha composed of several articulated appendicular the fourth/third distal tarsal ratio in maximum preaxial-postaxial bones, referred as an indeterminate archosaur by Lo pez-Martínez length. The ha, lpta, inf and dtIV/dtIII were all measured with the (2000), from the Maastrichtian site of Basturs-1 (Lleida, Catalonia, software Avizo 7.1®. The shape and size of the third and fourth Spain; Fig. 2), which is tentatively assigned to a large member of distal tarsals and fifth metatarsal, as well as positions of tubercles in Varaniformes. the latter, were the morphological traits considered in this study to Anatomical abbreviations. dt, distal tarsal; lpt, lateral plantar compare between species and clades. tubercle; mpt, medial plantar tubercle; mt, metatarsal; op, outer In order to obtain the complete appendicular 3D model, and the process. 3D models of each skeletal element, the specimen was processed in Institutional abbreviations. AMNH, American Museum of Natural the Non-destructive Techniques Laboratory of the Museo Nacional History, New York, USA; CAS, California Academy of Sciences, San de Ciencias Naturales, in Madrid, where it was CT-scanned to pro- Francisco, California, USA; CT, Ankara University, department of vide the 3D model according to the following technical parameters: Engineering Geology, C ̧ eştepe, Turkey; FMNH, Field Museum of 160 kV, 62 mA, 0.625 thick copper filter, 0.127-pixel size, 900 pro- Natural History, Chicago, Illinois, USA; GNM, Simon Janashia jections. The files obtained (DCM and tiff files) were processed Museum of Georgia, Georgian National Museum, Tbilisi, Georgia; using the software Avizo 7.1® in through the axes XY, XZ and YZ. IGM, Institute of Geology, Mongolian Academy of Sciences, Ulaan Both the bone material and the sediment were reconstructed on Bataar, Mongolia; IRScNB, Institut Royal des Sciences Naturelles de the 3D model separately, so that the latter could be virtually Belgique, Brussels, Belgium; KNM, Kenya National Museum, Nai- removed. Finally, the surface of the specimen as a whole was robi, Kenya; LGPUT, Laboratory of Geology and Palaeontology of the generated. University of Thessaloniki, Thessaloniki, Greece; MAFI,  Magyar  Allami Fo €ldtani Inte zet (Hungarian Geological Institute), Budapest, 3. Systematic paleontology Hungary; MCD, Museu de la Conca Della , Lleida, Spain; MCSNT, Museo Civico di Storia Naturale di Trieste, Italy; MNCN, Museo Squamata Oppel, 1811 Nacional de Ciencias Naturales-CSIC, Madrid, Spain; MNHN AC, Anguimorpha Fürbringer, 1900 Anatomie Compare e, Muse um National d’Histoire naturelle, Paris, ?Varaniformes Conrad, 2008 France; MPUR, Museo Paleontologico dell’Universita  di Roma, Lazio, ?Varaniformes gen. et sp. indet (Figs. 3e5) Italy; MSNM, Museo di Storia Naturale di Milano, Italy; NCSM, North Carolina Museum of Natural Sciences, North Carolina, USA; Material. MCD-8827, an articulated left hindlimb, preserving two NHMUK, Natural History Museum of London, UK; RPl, Ravin de la complete tarsals and four metatarsals (Figs. 3e5), the mtV being the Pluie locality, acronym of the collections of the LGPUT; TMM, Texas only complete of them. Memorial Museum (The University of Texas at Austin), Austin, Locality and Horizon. Basturs-1 fossil site (Fig. 2), uppermost Texas, USA; UANL-FCT, Universidad Auto noma de Nuevo Leo n, Cretaceous (Maastrichtian). Tremp Synclinal, Lleida, Catalonia, Facultad de Ciencias de la Tierra, Linares, Nuevo Leo n, Mexico; UCM Spain (Lopez-Martínez, 2000; Csiki-Sava et al., 2015; Gaete et al., MACV, Museo de Anatomía Comparada de Vertebrados, Uni- 2015; Fondevilla et al., 2018, 2019). versidad Complutense de Madrid, Madrid, Spain; UF, University of Description. MCD-8827 measures 7.06 cm in its maximum length Florida, Gainesville, USA; UMMZ, University of Michigan Museum and 3.11 cm in its maximum width. Six articulated bony elements of Zoology, Michigan, USA; USNM, National Museum of Natural can be identified: two distal tarsals (the third and the fourth) and History, Smithsonian Institution, Washington D.C., USA; YPM, Yale four metatarsals (from the second to the fifth) (Fig. 3AeF). Meta- Peabody Museum, New Haven, Connecticut, USA; ZPAL, Zakład tarsals from the second to the fourth lack their distal parts Paleobiologii, Polska Akademia Nauk (Paleobiological Institute, (Fig. 3AeF), so their total original length is unknown (see Table 1), Polish Academy of Sciences), Warsaw, Poland. and the fifth metatarsal is completely preserved (Fig. 3AeF). 2 ndez, A. Bolet, A. Torices et al. A. Cabezuelo Herna Cretaceous Research 131 (2022) 105094 Fig. 1. Main localities of the “varanoid” fossil taxa compiled for this study and fossil specimen MCD-8827, corresponding to a partial left pes attributable to ?Varaniformes from the Maastrichtian of Basturs-1 (Lleida, Spain). “Varanoidea” geographical range during the Cretaceous showing a main distribution throughout the supercontinent Laurasia. A, Eu- ropean, North African and middle East localities: 1, Salas de los Infantes, Viajete Site (Burgos, Spain) (BarremianeAptian); 2, La Cabanea Formation (Asturias, Spain) (upper Cen-  omanian); 3, Castillo-Lasarte (Alava, Spain) (upper Campanian) and Albaina, Laneo quarry (Condado de Trevineo, Burgos, Spain) (upper Maastrichtian); 4, Lo Hueco (Cuenca, Spain) (upper Campanianelower Maastrichtian); 5, Aveiro (Portugal) (upper Campanianelower Maastrichtian); 6, Viso (Portugal) (upper Campanianelower Maastrichtian); 7, Font de la Carrasca Quarry, Castalla (Alicante, Spain) (upper Maastrichtian); 8, Basturs-1 (Lleida, Catalonia, Spain) (Maastrichtian); 9, Auzas Marls (France) (upper Maastrichtian); 10, Cruzy (Herault) and Montse ret (Corbieres) (France) (upper Campanianelower Maastrichtian); 11, Madame Island (France) (upper Cenomanian); 12, Sainte-Maure (Indre-et-Loire, France) (middle Turonian); 13, Mesvin (Hainault, Belgium); 14, DIMAC quarry, Hesseltal Formation (Germany) (lowermost Turonian); 15, Piotrawin (Poland) (upper Campanian) and Nasiłow (Poland) (upper Maastrichtian); 16, Maruszo w (Poland) (upper Maastrichtian); 17, Komen (Slovenia) (upper Cenomanian); 18, Hvar Island (Croatia) (upper Cenomanian); 19, Nardo  (Lecce, Puglia, Italy) (upper Campanian, lower Maastrichtian); 20, Charquieh, Khneifiss, Bardeh and Soukhneh (Syria) (Maastrichtian); 21, Hakel (Lebanon) (loweremiddle Cenomanian); 22, Judean Hills (Israel) (upper Cenomanianelower Turonian); 23, Goulmima (Er-Rachidia, Morocco) (lower Turonian); 24, Youssoufia (Morocco) (Maastrichtian). B, Asian localities: 25, Dzharakuduk (Uzbekistan) (Turonian/Coniacian); 26, Zhirkindek (Kazakhstan) (TuronianeConiacian); 27, Khermeen-Tsav and Hirmiin Tsav (Gobi Desert, Mongolia) (SantonianeCampanian and ?middle Campanian); 28, Khulsan, Ukhaa Tolgod and Uuden Sair (Gobi Desert, Mongolia) (?upper Santonian/?lower Campanian, ?middle Campanian, upper Campanian); 29, Shabarakh Usu (Gobi Desert, Mongolia) (SantonianeCampanian); 30, To €gro € kgiin Shiree (Gobi Desert, Mongolia) (?middle Campanian); 31, Bayan Mandahu (Urad Houqi, Inner Mongolia, China) (middle Campanian); 32, Kuwajima (Honshu, Japan) (BerriasianeValanginian); 33, Boseong, (Chollanam-do, South Korea) (Cam- panian); 34, Nankang (Jiangxi, China) (Maastrichtian); C, American localities: 35, Milk River Area (Alberta, Canada) (Campanian); 36, Lance Formation (Wyoming) (Maastrichtian); 37, Emery County (Utah, USA) (AlbianeCenomanian); 38, Kaiparowits Formation (Utah, USA) (Campanian); 39, Cedar Hill (Dallas County, Texas) (middle Turonian); 40, Vallecillo (Nuevo Leo  n State, Mexico) (lower Turonian); 41, Lebrija (Colombia) (lower Coniacian); 42, Coello (Colombia) (Campanian); 43, The Upper Magdalena Valley (Colombia) (Turonian). Data according to Gilmore (1928, 1943), Arambourg (1952), Estes (1964), Borsuk-Białynicka (1984), Nessov (1981), Antunes and De Broin (1988), Rage (1989), Norell et al. (1992, 2008), Alifanov (1993), Cifelli and Nydam (1995), Gao and Hou (1996), Lingham-Soliar (1996), Buffetaut et al. (1997), Dal Sasso and Pinna (1997), Norell and Keqin (1997), Bardet et al. (1999, 2000, 2003, 2006, 2013a, b), Keqin and Norell (2000), Nydam (2000, 2013), Kordikova et al. (2001), Peng et al. (2001), Laurent et al. (2002), Machalski et al. (2003), Pierce and Caldwell (2004), Rage and Ne raudeau (2004), Bell and Polcyn (2005), Haber and Polcyn (2005), Evans et al. (2006), Smith and Buchy (2008), Vullo et al. (2009), Houssaye et al. (2010), Palci and Caldwell (2010), Conrad et al. (2011b), Pa ramo-Fonseca (2011), Mo et al. (2012), Houssaye et al. (2013a, b), Yi and Norell (2013), Ortega et al. (2015), Park et al. (2015), Pereda-Suberbiola et al. (2015), Paparella et al. (2018), Smith et al. (2019). The fourth distal tarsal in MCD-8827 is rhomboidal in shape and is posterodistally and the fifth metatarsal posteroproximally through slightly longer in its preaxial-postaxial axis than in its proximal- a larger surface (Fig. 3C). Proximally, in its inner surface, the fourth distal axis (Fig. 3BeC). This bony element articulates medi- distal tarsal bears a distinct tongue-in-groove concavity (Fig. 3BeC odistally with the third distal tarsal through a small contact surface red arrows) which we interpret as the articular facet for the (Fig. 3C). The fourth distal tarsal also contacts the fourth metatarsal astragalocalcaneum. The third distal tarsal is smaller in size, nearly 3 ndez, A. Bolet, A. Torices et al. A. Cabezuelo Herna Cretaceous Research 131 (2022) 105094 Fig. 2. Geographical location of the Maastrichtian fossil site of Basturs-1 (Lleida, Spain) where the fossil specimen MCD-8827, corresponding to a partial left pes attributable to ? Varaniformes, was found. The geographical coordinates of the site, 42 100 15.12800 N, 1 10 1.31500 E, were obtained from the georeferenced map corresponding to Gaete et al. (2015: fig. 2). half the width of the fourth distal tarsal (Fig. 3C). This bony element has a moderately long longitudinal axis (Fig. 4AeB), and it bears a is slender and more elongated than the fourth distal tarsal, with a well-developed proximal head with squarish contours, isolated posterior process directed towards the plantar surface (Figs. 4CeD, from the rest of the metatarsal and so setting up a ‘long-necked’ 5A). The third distal tarsal articulates with the fourth distal tarsal at configuration (Fig. 5AeC). The fifth metatarsal is distinguished by its proximal-most facet. Moreover, this element articulates ante- its double angulation, here referred as ‘hooking angle’ and ‘inflexion rodistally with the second metatarsal, posterodistally with the third angle’ (Fig. 5C, E). Metatarsals from two to four have rounded cross- metatarsal and with the fourth metatarsal through its most post- sections and are laterally flattened (Fig. 3EeF) with a distinct eroproximal facet (Figs. 3BeC, 5A). The position of the third distal dorsal-plantar development (Fig. 4CeD), most noticeable on the tarsal is noteworthy in that it lies between the second and the third fourth metatarsal. metatarsals, contacting them by means of a wedge-like distal tip The hooking angle (ha) and the inflexion angle (inf) are 122.4 and (Figs. 3BeC, 5A). 120 respectively (see Table 1 and Supplementary information 2 in The second metatarsal articulates proximally through its postaxial Appendix B). The angle of the lateral plantar tubercle in relation to facet with the anterodistal facet of the third distal tarsal and with the other two (lpta) is estimated to be about 82.6 due to preser- the third metatarsal posteroproximally (Fig. 3BeC). The third vation issues (see Table 1 and Supplementary information 2 in metatarsal articulates anteroproximally with the third distal tarsal Appendix B). Angulation in MCD-8827 results in it being sub- and with the fourth metatarsal posteroproximally. Both the second pentagonal in shape (Fig. 5D). The fourth distal tarsal is roughly and the third metatarsals bear moderately developed proximal twice the width of the third (dtIV/dtIII) (Fig. 3C, see Table 1). epiphyses (Fig. 3BeC). The fourth metatarsal articulates with the fourth distal tarsal through its proximal-most facet and, in its anteroproximal facet, a distinct contact with the third distal tarsal 4. Discussion occurs and bears a better developed epiphysis than the second and third metatarsals (Fig. 3BeC). The fifth metatarsal articulates 4.1. Systematic assignment of MCD-8827 proximally with the fourth distal tarsal and, despite contacting the fourth metatarsal, there is no direct articulation between the latter Identification of MCD-8827 as a member of Squamata. MCD-8827 with the fifth metatarsal (Figs. 3BeC, EeF, 5A). The fifth metatarsal shows two characters considered synapomorphies of Squamata, bears a partially eroded outer process (Figs. 4AeB, 5AeB), the base allowing its attribution to this clade: presence of a distinct ‘tongue- of which is preserved. Despite this partial preservation, its base in-groove’ articular surface on the fourth distal tarsal for the demonstrates that it was distinct and well developed (Fig. 5C). astragalocalcaneum (Fig. 3BeC) (Brinkman, 1979; Rewcastle, 1980; Ventrally, the fifth metatarsal possesses two well developed tu- Estes et al., 1988; Gauthier et al., 1988; Reynoso, 1998, 2000; Evans bercles and a slightly elevated area corresponding to the base of the and Wang, 2005, 2010; Conrad, 2006a; Sullivan, 2010; Conrad et al., outer process (Fig. 5C). The lateral plantar tubercle is elongated, 2011b); and presence of a specialized fifth metatarsal with double robust and has a rounded ovoid tip that extends close to the medial angulation and well developed plantar tubercles (Fig. 5C, E) (Estes plantar tubercle. The medial plantar tubercle also bears a rounded et al., 1988; Carroll and DeBraga, 1992; Reynoso, 2000; Evans, 2003; ovoid tip that is less robust (Fig. 5C). The outer process is distally Conrad and Norell, 2007; Jerez, 2012). placed from both plantar tubercles and seems less prominent than A fourth-third distal tarsal proportion of roughly two, as docu- both lateral and medial plantar tubercles (Fig. 5C). The fifth meta- mented in this study and others (Rieppel, 1992; Conrad, 2006a; tarsal is proportionally more robust than the other metatarsals. It Rieppel and Grande, 2007; Smith and Buchy, 2008; Evans and 4 ndez, A. Bolet, A. Torices et al. A. Cabezuelo Herna Cretaceous Research 131 (2022) 105094 Fig. 3. Original material and digital reconstruction of MCD-8827 fossil specimen, corresponding to a partial left pes attributable to ?Varaniformes, from the Maastrichtian of Basturs-1 (Lleida, Spain). Original material (A, D) and reconstructed 3D model from CT-Scan (BeC, EeF) before (B, E) and after (C, F) surrounding matrix was removed (transparent red) in dorsal (AeC) and plantar views (DeF). Arrows indicate the tongue-in-groove articulation of dtIV exclusive of Squamata. Scale bar: 10 mm. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.) 5 ndez, A. Bolet, A. Torices et al. A. Cabezuelo Herna Cretaceous Research 131 (2022) 105094 Fig. 4. Original material and digital reconstruction of MCD-8827 fossil specimen, corresponding to a partial left pes attributable to ?Varaniformes, from the Maastrichtian of Basturs-1 (Lleida, Spain). Original material (A, C) and reconstructed 3D model (B, D) in left lateral (outer face) (AeB) and right lateral (inner face) (CeD) views. Scale bar: 10 mm. Fig. 5. Reconstruction of the articulations and morphology of the metatarsal V of MCD-8827, corresponding to a partial left pes attributable to ?Varaniformes, from the Maas- trichtian of Basturs-1 (Lleida, Spain). A, main articulations shown between tarsal and metatarsal elements with mtV, where the transparent elements represent those which articulate with the latter. BeE, general morphology of mtV shown in dorsal (B), plantar (C), proximal (D) and lateral views (E). Arrows indicate the long-necked hooked mtV configuration typical of Lepidosauromorpha. Plantar tubercles: lpt (orange); mpt (green); op (purple). Scale bars: A, E, 6 mm; B, C, 10 mm; D, 7 mm. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.) Wang, 2010; Conrad et al., 2011b), can be recognized as exclusive to study show a fourth-third distal tarsal proportion of approximately Squamata (Table 2), being also shared by MCD-8827 (Table 1). In three (see Table 2). This was also observed in the S. punctatus this sense, the Sphenodon punctatus specimens analysed in this specimens analysed in other works (e.g. Brinkman, 1979; Benton, 6 ndez, A. Bolet, A. Torices et al. A. Cabezuelo Herna Cretaceous Research 131 (2022) 105094 Table 1 1985; Gauthier et al., 1988). This character, along with a rounded Tarsal and metatarsal measures of fossil specimen MCD-8827, corresponding to a centrally placed lateral plantar tubercle, unique for S. punctatus, in partial left pes attributable to ?Varaniformes, from the Maastrichtian of Basturs-1 (Lleida, Spain). Length measures of metatarsals II-IV are not representative of the combination with a moderately developed outer process, and a actual element length since they are fragmented in their distal part. Hooking (ha), poorly developed medial plantar tubercle (none of them shared inflexion (inf) and lateral plantar tubercle (lpta) angles were only measured in mtV. with the Basturs-1 specimen analysed here), differentiates the fifth Measures Anatomical element metatarsal of S. punctatus from that of the squamates (see Fig. 6A,G) (Brinkman, 1979; Gauthier et al., 2012; Regnault et al., 2016; mtII mtIII mtIV mtV dtIV/dtIII Borsuk-Białynicka, 2018). Radius (cm) 0.52 0.68 0.8 0.57 e Comparison of MCD-8827 with the squamate clade Gekkota. The Length (cm) 4.05 4.42 5.55 2.68 fossil specimen MCD-8827 differs from Gekkota in having a slender ha (o) 122.4 and elongated fifth metatarsal with a “pedunculated” lateral e inf (o) 120 lpta (o) 82.6 plantar tubercle capped with an ovoid-rounded protuberance. In Proportion 1.83 contrast, the gekkotan condition shows a rather short fifth Table 2 Tarsal and metatarsal V measure ranges in the Lepidosauria taxa analysed in the study. The table shows a summary of the main values obtained for the hooking angle (ha) and the proportion between the dtIV and dtIII (dtIV/dtIII) from the lepidosaur specimens here studied (see Supplementary information 2 in Appendix B). Measures Taxon Squamata Sphenodontia Iguania Anguimorpha Scincoidea Lacertoidea Sphenodon MtV ha (o) 130.1-?142.1 119.4e136.6 131e142 ?134-145 115.1 dtIV/dtIII 1.94e2.09 ?1.75e2.22 1.99e2.04 1.90e2 2.93e3 Fig. 6. Tarsal and metatarsal traits in some lepidosaur taxa examined in this study. AeF, morphology of the tubercles of the mtV; GeK, angulation in proximal view, the upper margin corresponding to the dorsal region; LeM, dtIV/dtIII proportion; and NeO, inflexion angle in some species of Lepidosauria: Sphenodon punctatus (A, G), Amblyrhynchus cristatus (B), Shinisaurus crocodilurus (C, I), Xenosaurus rectocollaris (D), Heloderma horridum (E), Varanus bengalensis (F, M), H. suspectum (J, L, N), Iguana iguana (H), V. rudicollis (K), V. griseus (O). Plantar tubercles: lpt (orange); mpt (green); op (purple). DtIII (yellow) y dtIV (blue). Dashed lines in red represent the articular facet for dtIV. Drawings not to scale. Scale bars: F, K, L, 2 mm; J, N, O, 1 mm; M, 4 mm. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.) 7 ndez, A. Bolet, A. Torices et al. A. Cabezuelo Herna Cretaceous Research 131 (2022) 105094 metatarsal with a rather bulbous and “non-pedunculated” tubercle overlying position upon the third distal tarsal (see fig. 36 in (see Daza and Bauer, 2012; Scherz et al., 2017), and raised plantar Gilmore, 1942). MCD-8827, instead, has a rhomboidal fourth distal tubercles, really close to the articulation facet and between each tarsal that lies completely upon the third distal tarsal (Fig. 5A). other (Russel et al., 1997; Scherz et al., 2017). Gekkotans tend to Additionally, the proximal head in the fifth metatarsal of the three acquire a symmetrical foot as a result of a shorter fourth metatarsal specimens mentioned of P. sternbergi is not as developed as in compared to the third one (Russel et al., 1997; Simo ~ es et al., 2016), a MCD-8827. Besides, the specimen USNM 15568 has measures for all condition that cannot be confirmed in MCD-8827 due to the frag- the five metatarsals, showing a mtIV/mtV ratio of 2.77, which is mentary state of these bony elements. Additionally, in gekkotans apparently higher than that estimated for MCD-8827 (about 2.07). the proximal head of the fourth metatarsal is extremely broadened On the other hand, the Yale Peabody Museum specimen of so that the angle between the shafts of the third and fifth meta- Polyglyphanodon sternbergi (YPM VP 003230) preserves the fifth tarsal increases and, consequently, the imbrication amongst the metatarsal in both dorsal and ventral views. In dorsal view, the fifth metatarsals is proximally reduced (Daza and Bauer, 2012; Simo ~ es metatarsal also shows a less developed proximal head than that of et al., 2016). This condition is not shared with MCD-8827 since the fifth metatarsal of MCD-8827. In ventral view, the fifth meta- the third metatarsal proximally overlaps a great portion of the tarsal of P. sternbergi bears two distinct rounded and ‘not-pedun- fourth (Figs. 3, 5A). culated’ plantar tubercles that resemble those of the teiid Ameiva Comparison of MCD-8827 with the squamate clades Scincoidea ameiva, but with the medial plantar tubercle situated right in the and Lacertoidea. The scincoids Cordylus angolensis, C. cordylus, edge of the articular facet with the fourth distal tarsal and, thus, C. namakuiyus, C. phonolithos, Corucia zebrata, Ctenotus schom- differing as well from those of MCD-8827. burgkii, Egernia whitii, Smaug barbertonensis, S. giganteus and Tri- A specimen of Gilmoreteius (Macrocephalosaurus) chulsanensis bolonotus sp. and the lacertoids Ameiva ameiva, Ecpleopus (ZPAL-I/14) preserving the hindlimb was described in detail by gaudichaudii, Heterodactylus imbricatus, Leposoma scincoides, Sulimski (1975). The foot is illustrated both in dorsal and ventral Micrablepharus maximiliani, Placosoma cordylinum and Takydromus views. In dorsal view, the third distal tarsal lies completely lateral to sexlineatus (as members of their corresponding clades for which the fourth distal tarsal unlike in Polyglyphanodon sternbergi (YPM observations were obtained) tend to have a stout proximal head of VP 003230) and the fossil specimen from Basturs-1 (MCD-8827). the fifth metatarsal which, in ventral view, is notably widened (see The fourth distal tarsal is subrectangular in shape (see fig. 11A1eA2  n fig. 6 in Jerez, 2012, and fig. 5 in Cer  anský and Smith, 2019). MCD- in Sulimski, 1975) rather than rhomboidal as in MCD-8827 8827, however, has a fifth metatarsal with the proximal part (Fig. 3AeC). As in P. sternbergi, the proximal head of the fifth resulting in a well-developed head that is somehow elongated to- metatarsal is not as developed as in MCD-8827. In ventral view, the wards and behind the fourth distal tarsal (Fig. 5A). Moreover, in fifth metatarsal of ZPAL-I/14 is illustrated as bearing a distinct these two clades the medial plantar tubercle tends to be situated lateral plantar tubercle which seems ‘not-pedunculated’ and a apart from the outer process and, together with the lateral plantar medial plantar tubercle hardly developed, thus differing from the tubercle, they develop in a dorsal-plantar plane in a “heel-like” fossil specimen MCD-8827 (Fig. 5C). Besides, the mtIV/mtV ratio in manner (see fig. 11F in Müller, 2001; fig. 4 eAmphiglossus ornaticeps ZPAL-I/14 (G. chulsanensis) is 2.90, which is much higher than that plate, central imagee in Miralles et al., 2015; fig. 7C in Tałanda, estimated for the fossil specimen MCD-8827 from Basturs-1 (about 2018; and fig. 5 in Cer n anský and Smith, 2019), and with moder- 2.07). ate developed apophyses of the tubercles. In contrast, MCD-8827 Comparison of MCD-8827 with the squamate clade Mosasaur- bears two plantar tubercles that are more longitudinally devel- iformes. European mosasauriforms preserving the tarsus include oped, relatively closer to each other and with bigger ovoid Acteosaurus tommasinii from the upper Cenomanian of Komen apophyses. (Slovenia) and Primitivus manduriensis from the upper Campanian/ Comparison of MCD-8827 with the squamate clade Iguania. The lower Maastrichtian of Nardo  (Italy). MCD-8827 differs from fossil specimen MCD-8827 differs from the members of Iguania in A. tommasinii in the hooked fifth metatarsal, which in the latter has having a fifth metatarsal morphology presenting well-developed, a hookless configuration (Palci and Caldwell, 2010). MCD-8827 ovoid-rounded tubercles and a protuberant outer process shares with P. manduriensis a fifth metatarsal with a proximal (Fig. 5C), in contrast to the iguanian condition where the outer expanded head, but the latter differs from MCD-8827 in having a process is barely developed and the plantar tubercles tend to ac- slightly curved fifth metatarsal which is notably shorter (1.04 cm; quire a more elongated shape with the medial plantar tubercle, Paparella et al., 2018) than that of MCD-8827 (2.68 cm) making a usually the most developed, generally resulting in a ‘downward- mtIV/mtV ratio of 1.05, at least half the value estimated for MCD- pointing’ structure (e.g. Bronchocela cristatella or Sceloporus undu- 8827 (2.07). Forms from other continents include the lower/mid- latus). This feature is much more evident in the species within the dle Cenomanian Aphanizocnemus lebanensis of Hakel (Lebanon) and family Iguanidae (e.g. Amblyrhynchus cristatus, Ctenosaura similis or the lower Turonian Vallecillosaurus donrobertoi of Nuevo Leo n Iguana iguana) (see Brinkman, 1979, 1980; Borsuk-Białynicka, 2018; (Mexico). MCD-8827 differs from A. lebanensis in the fifth meta- and Fig. 6B, H in this work). tarsal, which is not hooked in the latter, and in the dorso-ventral Comparison of MCD-8827 with the squamate clade Borioteiioidea. compression of metatarsals (Dal Sasso and Pinna, 1997), these The clade Borioteiioidea (or Polyglyphanodontia sensu Gauthier two traits being characteristic of aquatic forms (mosasauriforms) et al., 2012) includes large fossil taxa (e.g. Polyglyphanodon, Gil- (DeBraga and Carroll, 1993; Dal Sasso and Pinna, 1997; Lee et al., moreteius) occasionally represented by skeletons preserving hin- 2016; Paparella et al., 2018; Gonçalves Augusta, 2019). MCD-8827, dlimb elements. The three specimens of Polyglyphanodon sternbergi in contrast, presents metatarsals that are laterally flattened described by Gilmore (1942) (USNM 15568, USNM 15816 and (Fig. 4). MCD-8827 differs from V. donrobertoi in the placement of USNM 15817) preserve the entire foot (see fig. 36 in Gilmore, 1942). the third and fourth distal tarsals, these elements being situated However, the pes of these specimens are preserved and illustrated one after the other in the latter and not lying one upon each other in dorsal view and the fifth metatarsal is not described in detail, as it occurs in MCD-8827; in the less pronounced inflexion of the hence, no anatomical features of the plantar tubercles could be fifth metatarsal; and, finally, in the length of the fifth metatarsal, compared. Nonetheless, some features could be compared: the shorter (1.01 cm) (Smith and Buchy, 2008) than in MCD-8827, specimen USNM 15568 possesses a “flattened” fourth distal tarsal making a mtIV/mtV ratio of 1.7 (in contrast to that of MCD-8827, (referred as “tarsale 4” in Gilmore, 1942) that acquires a slightly with an estimated minimal value of 2.07). 8 ndez, A. Bolet, A. Torices et al. A. Cabezuelo Herna Cretaceous Research 131 (2022) 105094 Comparison of MCD-8827 with the squamate clade Anguimorpha. lateral plantar tubercle and the outer process (Fig. 6E; see also MCD-8827 shares with the pes of Anguimorpha the presence of a Conrad, 2006a,b). In both H. horridum and H. suspectum the third fifth metatarsal with well-developed medial and lateral plantar and fourth distal tarsals are placed one after another (Fig. 6L), the tubercles, the latter being elongated; the elongated condition of the hooking angles are around 130 and the inflexion angles are pretty metatarsal long axis (e.g. Evans and Wang, 2005; Conrad, 2006a; acute (81.6 and 88 respectively), therefore, differing from MCD- see Fig. 5C); and a hooking angle lower than 137 (see Table 2). 8827. Within anguimorphs, MCD-8827 differs from the xenosaurids (e.g. The middle Campanian Gobiderma pulchrum of To €gro €kgiin Xenosaurus grandis and X. rectocollaris) in the mediodistally posi- Shiree (Mongolia) also shares the ‘helodermatid’ condition of the tioned lateral plantar tubercle, and in the outwards inclination of its position of the distal tarsals (one settled after the other). Never- “peduncle” (see fig. 9B in Conrad, 2006a and Fig. 6D in this work). theless, its fifth metatarsal has a distally placed lateral plantar tu- Both X. grandis and X. rectocollaris have a wider hooking angle bercle (Conrad et al., 2011b), which is much smaller in length (less (135 ) than MCD-8827 (122.4 ) (see Supplementary information 2 than 1 cm), differing from MCD-8827 in this regard. However, the in Appendix B). reported fifth metatarsal that “is only slightly shorter than II and IV” The shinisaurid Shinisaurus crocodilurus has a fifth metatarsal is not evident in the provided figure (see fig. 51A in Conrad et al., with a moderate outer process and a lateral plantar tubercle placed 2011b). It is finally important to note that not all phylogenetic an- next to the articular condyle of the metatarsal (Fig. 6C, I) (Conrad, alyses recovered G. pulchrum as a monstersaur. Gauthier et al. 2006a,b; Bhullar, 2011; Conrad et al., 2011b). The fifth metatarsal (2012) recovered it on the stem of a monophyletic “Varanoidea”, of the Eocene shinisaurid Bahndwivici ammoskius, from Wyoming whereas in Reeder et al. (2015) it was placed, together with Aiolo- (USA), resembles that of S. crocodilurus in having a lateral plantar saurus oriens and Estesia mongoliensis, as sister to varanids. The pes tubercle placed distally, near the articular condyle (Conrad, 2006b), of Palaeosaniwa canadensis (Monstersauria) from the Upper as well as a medial plantar tubercle and outer process similar in Cretaceous of Canada is known (Balsai, 2001), but has not been shape and placement to those found in S. crocodilurus, hence described in detail, and comparison is thus not possible. differing from MCD-8827. Regarding varaniforms, MCD-8827 more closely resembles this The anguids Abronia graminea, Diploglossus millepunctatus, group rather than monstersaurs in: Varanus-like plantar tubercles Elgaria coerulea and Mesaspis moreletii have a fifth metatarsal with similar in their ovoid shape and relative position; a medial plantar a moderate outer process, a medial plantar tubercle slightly bigger tubercle similar in size to that of the lateral plantar tubercle than the lateral plantar tubercle, somehow intermediate between (Figs. 5C, 6F) (see also Rewcastle, 1980; Conrad, 2006a); and the helodermatids and varanids (see below), and a well-developed relative positions of the third and fourth distal tarsals in MCD-8827, proximal head of the fifth metatarsal. On the contrary, MCD-8827 shared with Varanus spp., whose fourth distal tarsals always lie has a fifth metatarsal with a medial plantar tubercle not bigger completely upon the third distal tarsals (Figs. 5A, 6M) (see also than the lateral plantar tubercle, a bigger development of the Owen, 1866; Goodrich, 1942; Benton, 1985; Brinkman, 1979, 1980; proximal head and a smaller hooking angle (122.4 ) than the Lee et al., 2016). Additional features help in tipping the balance anguids above mentioned (133o-136.6 ). towards varaniform against monstersaur affinities. MCD-8827 Rieppel and Grande (2007) mentioned a fifth metatarsal bearing more closely resembles varaniforms than helodermatids in hav- an “expanded head with squarish contours” as a character that the ing: a hooking angle of 122.4 , which falls within the range ob- varanid Saniwa ensidens shares with other “varanoids”. However, tained for Varanus and Lanthanotus specimens examined in this other anguimorphs here studied show a similar configuration (e.g. study (between 119.4 and 122.6 , the latter value corresponding to Abronia graminea, Mesaspis moreletii or Xenosaurus rectocollaris). Lanthanotus) and out of the range of Heloderma horridum and Similarly, MCD-8827 resembles the pes of helodermatids and var- H. suspectum (about 130 ) (see Supplementary information 2 in anids in having these squarish contours along with well-developed Appendix B; see also Rieppel, 1980; Conrad, 2006a); and an plantar tubercles generally placed close to each other (Figs. 5C, inflexion angle of 120 closer to the range of Varanus spp. than to 6EeF) (see Rieppel and Grande, 2007). However, note that, Heloderma spp. (81o-88 ) (see Supplementary information 2 in because current molecular and combined phylogenies regard shi- Appendix B). MCD-8827 also differs from the extant members of nisaurs as more closely related to varanids than to helodermatids Heloderma in the morphology of the fifth metatarsal in lateral view, (e.g. Conrad et al., 2011a; Wiens et al., 2012; Burbrink et al., 2019), where the inflexion and the lateral plantar tubercle is less pro- the similarities between helodermatids and varanids noted above nounced (Varanus-like) (Figs. 5E, 6O) rather than acute and protu- cannot be regarded as indicative of shared ancestry. berant, as in H. horridum and H. suspectum (Fig. 6N) (see also Lee, Large fossil anguimorphs include members of Monstersauria 1997; Conrad, 2006b; Borsuk-Białynicka, 2018). (Heloderma plus its stem), Varaniformes (Varanidae plus its stem), Despite MCD-8827 resembling the general morphology of the and indeterminate “varanoids”, the latter term traditionally used varanid pes, the fossil specimen clearly shows some features that for forms more similar to Heloderma and Varanus than to other differ from the extant Varanus: it differs from the extant members anguimorphs, although the group is now considered as poly- of Varanus in its inflexion angle, 120 in MCD-8827, being wider in phyletic (see above and also Burbrink et al., 2019). Regarding the species of Varanus (approximately 140 ) (see Supplementary “Varanoidea”, no anatomical comparison between MCD-8827 and information 2 in Appendix B; and Lee, 1997; Borsuk-Białynicka, the fossil “varanoids” of the Iberian Peninsula is possible due to the 2018); in the third distal tarsal, which in Varanus spp. acquires a lack of tarsal/metatarsal elements preservation in those specimens. subtriangular shape (Fig. 6M) (see Brinkman, 1979, 1980; Goodrich, However, some European and non-European monstersaurs and 1942; Lee et al., 2016) whereas in MCD-8827 is elongated and with varaniforms preserve tarsal/metatarsal elements to be compared a pointing-backwards process (Fig. 5A); in the angulation, with a with the fossil specimen of Basturs-1 (see section Extinct species of signature trapezoidal shape in the Varanus specimens here ana- Supplementary information 1 in Appendix A). lysed (Fig. 6K) (see “angulation” in Borsuk-Białynicka, 2018) but Regarding monstersaurs, MCD-8827 differs from the extant with a subpentagonal shape in MCD-8827 (Fig. 5D); and in the helodermatids Heloderma horridum and H. suspectum in their fifth reduction of the proximal articulation area of the fifth metatarsal, metatarsal with an enlarged medial plantar tubercle that expands this element not being in contact along its axis with the fourth reaching most of the surface of the articular facet with the fourth metatarsal in Varanus (Owen, 1866; Brinkman, 1980; Rieppel, 1980; distal tarsal, and which is much bigger in comparison with the Estes et al., 1988; Lee, 1997; Rieppel and Grande, 2007; Sullivan, 9 ndez, A. Bolet, A. Torices et al. A. Cabezuelo Herna Cretaceous Research 131 (2022) 105094 2010; El-Bakry et al., 2013; Borsuk-Białynicka, 2018), while in MCD- Cenomanian of USA (Nydam, 2000, Pianka et al., 2004; Yi and 8827 these two elements maintain a close contact between each Norell, 2013, Alifanov, 2018), whereas the earliest varaniforms other (Figs. 3AeF, 5A). Besides, MCD-8827 also differs from the recorded are not older than Coniacian or Santonian/Campanian in closest extant relative of Varanus, Lanthanotus borneensis, in the age (Borsuk-Białynicka, 1984; Rage and Auge, 1993; Kordikova et al., lateral plantar tubercle, which in the latter is placed distally, near 2001; Pianka et al., 2004). The fossil record seems to indicate an the articulation condyle of the fifth metatarsal (Rieppel, 1980, 1992; Asian origin for Varanidae and a North American origin for Hel- Lee, 1997; Conrad, 2006a; Conrad et al., 2011b). odermatidae, the latter originating from an Asian monstersaur-like With regards to fossil forms, no other Cretaceous varaniform form (Fig. 1B) (Pregill et al., 1986; Averianov and Danilov, 1997; than the Santonian or Campanian Telmasaurus grangeri specimen Alifanov, 2000; Nydam, 2000; Bhullar and Smith, 2008; Arida and (AMNH 6643), described by Gilmore (1943), preserves tarsal or Bo€ hme, 2010; Smith and Gauthier, 2013; Mead et al., 2015). metatarsal elements, but these elements were not described in MCD-8827 falls within a geologic time range (Maastrichtian) detail and the preservation of such elements hinder their descrip- when monstersaurs, varaniforms, and indeterminate related forms tion. In the Cenozoic, the European Paranecrosaurus feisti and the were relatively common components of the Laurasian fauna. North American Saniwa ensidens both preserve pes bones. The Nonetheless, varaniforms have not been confidently identified at lower Eocene S. ensidens specimen FMNH PR2378 presents a pes that time in Europe, since the oldest confirmed records in the typical of Varanidae (Rieppel and Grande, 2007), thus sharing with continent pertain to Saniwa orsmaelensis (lower Eocene of Belgium; Varanus the absence of a much bigger medial plantar tubercle and a Dollo, 1923) and Paranecrosaurus feisti (middle Eocene of Germany; fourth distal tarsal completely lied upon third distal tarsal, and Stritzke, 1983). Some of the specimens traditionally assigned to differing from MCD-8827 in their subtriangular third distal tarsal “Varanoidea” could potentially represent varaniforms, but none of without pointing-backwards process mentioned above. The P. feisti them is complete enough to warrant an unambiguous identifica- specimens HLMD-Me 13709 and SMF-ME 10954 share a similar tion. Varaniforms are known from the Upper Cretaceous of configuration of the articulation between the metatarsal V and the Mongolia (e.g. Cherminotus longifrons, Saniwides mongoliensis; Tel- distal tarsal IV with MCD-8827, due to the first of these bones ex- masaurus grangeri), Kazakhstan and China, as shown in Fig. 1B tends further back the latter (see Fig. 5A in this work and fig. 24AeB (Gilmore, 1943; Borsuk-Białynicka, 1984; Alifanov, 1993, 2000; Clos, in Smith and Habersetzer, 2021). Moreover, P. feisti and MCD-8827 1995; Gao and Hou, 1996; Keqin and Norell, 2000; Kordikova et al., share features such as the relative position of the third distal tarsal 2001; Fitch et al., 2006; Norell et al., 2008; Conrad et al., 2012). with respect to the fourth one (the latter lied upon the first one), Some authors have referred fossils from the Santonian or Campa- the configuration of both the lateral plantar tubercle and the outer nian and Turonian or Coniacian of Mongolia and Kazakhstan (Asia) process, and the grade of inflexion of the fifth metatarsal. None- to Saniwa and close forms (Alifanov, 1993; Kordikova et al., 2001, theless, MCD-8827 differs from P. feisti in the shape of the fourth respectively). If correct, this taxon would be the only varaniform distal tarsal in ventral view (being U-shaped in P. feisti; see infor- present both before and after the Cretaceous-Paleogene boundary, mation about the “Pohl-Perner specimen” in the Appendix 3B of since no other forms present in the uppermost Cretaceous have Smith and Habersetzer, 2021), and in the morphology of the third been recovered from the Paleocene (Longrich et al., 2012; Nydam, distal tarsal (being subtriangular and without pointing-backwards 2013). However, these specimens are, due to their fragmentary process in P. feisti). In the Iberian Neogene, Varanidae is repre- nature, best regarded as indeterminate varaniforms. To date, MCD- sented by Varanus marathonensis (Delfino et al., 2013; Georgalis et 8827 represents the sole specimen tentatively attributable to a al., 2017; Ivanov et al., 2017; Villa et al., 2018) for which elements of varaniform lizard in the Basturs-1 fossil site. The information the tarsus have not been yet described. gathered exclusively from this fragmentary specimen, altogether Considering all the characters available in the fossil specimen of with the scarce information on appendicular fossil material from Basturs-1 here studied and discussed above, it is assigned to this clade in the Upper Cretaceous of Europe, do not allow more Anguimorpha and tentatively referred to Varaniformes. accuracy in the determination. 4.2. Biogeographic implications for the Cretaceous squamate record 4.3. Size estimation of the individual from Basturs-1 The fossil record of large sized squamates in the Cretaceous is The most striking feature of MCD-8827 is its large size. Although dominated by mosasauriforms (mosasaurs and related taxa, see the fragmentary nature of the specimen precludes an accurate Fig. 1). This aquatic radiation (Bardet et al., 2003; Haber and Polcyn, estimation of the SVL of the taxon, a tentative approximation can be 2005; Evans et al., 2006) culminated in the successful mosasaurs, calculated. According to DeMar et al. (2017), the largest Mesozoic which greatly expanded during the Late Cretaceous (Fig. 1A, C) terrestrial fossil squamate would be Chianghsia nankangensis, an (Lingham-Soliar, 1996; Bardet et al., 1999, 2000, 2003, 2006, Upper Cretaceous monstersaur from China (Mo et al., 2012) with an 2013a,b; Machalski et al., 2003; Pierce and Caldwell, 2004; Rage approximate SVL of 1000 mm. Park et al. (2015), however, reported and Ne raudeau, 2004; Bell and Polcyn, 2005; Smith and Buchy, the even larger taxon Asprosaurus bibongriensis. Unfortunately, no 2008; Vullo et al., 2009; Pa ramo-Fonseca, 2011; Maka di et al., comparison is possible between these taxa and MCD-8827 because 2012; Pereda-Suberbiola et al., 2015; Paparella et al., 2018; Smith of the lack of shared elements among those preserved. A slightly et al., 2019). Among terrestrial squamates, large taxa include bor- smaller size specimen has been reported for the North American ioteiioids (e.g. Polyglyphanodon), monstersaurs and varaniforms. putative monstersaur Palaeosaniwa canadensis (~850 mm) but, The two latter groups would include forms related to hel- although hindlimbs are known (Balsai, 2001) they have not been odermatids and varanids respectively, plus a suite of forms tradi- described in detail and again comparison is not possible. The esti- tionally referred as “varanoids” that cannot be attributed to one or mated SVL of MCD-8827, as calculated from mtV length, would be the other. These were already present by the Lower Cretaceous comprised between that of these large monstersaurs and the bor- record (Fig. 1) with forms such as Arcanosaurus ibericus from the ioteiioid Polyglyphanodon sternbergi from the Upper Cretaceous of Barremian or Aptian of Spain (Houssaye et al., 2013b), and inde- North America, with an estimated SVL of 450 mm. A regression line terminate taxa from the Aptian and Albian of Mongolia and USA calculated from the mtV length and SVL of 29 fossil and extant (Alifanov, 1993; Cifelli and Nydam, 1995). The earliest clear record squamates, allowed to predict a SVL of 580.96 mm for MCD-8827 of Monstersauria is Primaderma nessovi from the Albian or (Fig. 7). According to the minimum SVL value of 600 mm 10 ndez, A. Bolet, A. Torices et al. A. Cabezuelo Herna Cretaceous Research 131 (2022) 105094 Fig. 7. Size estimate for the fossil specimen of Basturs-1 (MCD-8827) based on comparisons of the ln of the mtV length across a selection of 29 fossil and extant squamates. MCD- 8827, whose mtV is almost 27 mm, is represented by a “cross” symbol, and corresponds with an estimated SVL of 581 mm. Numbers correspond to: 1, Varanus dumerilii (YPM-HERR 012148); 2, Lanthanotus borneensis (FMNH-134698); 3, V. exanthematicus (YPM-HERR 019119); 4, V. acanthurus (FMNH-97862); 5, Sauromalus varius (YPM-HERR 019215); 6, V. jobiensis (YPM-HERR 011074); 7, Heloderma suspectum (AC-1966-100); 8, V. prasinus (YPM-HERR 010328); 9, V. beccarii (YPM-HERR 013267); 10, V. salvator (YPM-HERR 011064); 11, V. beccarii (YPM-HERR 011899); 12, H. suspectum (YPM-HERR 016818); 13, V. dumerilii (YPM-HERR 011038); 14, V. exanthematicus (YPM-HERR 013940); 15, V. exanthematicus (YPM-HERR 011063); 16, V. rudicollis (YPM-HERR 011144); 17, V. bengalensis (YPM-HERR 011028); 18, V. salvator (MNCN-13818); 19, V. prasinus (YPM-HERR 011747); 20, Macro- cephalosaurus chulsanensis (ZPAL MgR-I/14); 21, V. salvator (YPM-HERR 011043); 22, S. varius (YPM-HERR 019217); 23, Saniwa ensidens (USNM PAL 617520); 24, Hydrosaurus pustulatus (YPM-HERR 016563); 25, H. pustulatus (YPM-HERR 014869); 26, V. varius (YPM-HERR 016800); 27, S. ensidens (FMNH PR2378); 28, S. ensidens (FMNH PR2380); 29, V. komodoensis (TMM-M-17921). specified by Conrad et al. (2012), the Basturs-1 specimen would be Basturs-1 is a relevant European dinosaur egg site (e.g. De close to the minimum size for being considered a giant terrestrial Lapparent, 1958; Sander et al., 1998), so this specimen seems to lizard. However, note that other lizards traditionally regarded as represent yet another example of an interesting association be- giant, like large fossil forms of Gallotia from the Canary Islands, are tween large anguimorphs and dinosaur egg sites. Basturs-1 fossil much smaller than this, with a maximum SVL of 500 mm (Barahona record is dominated by titanosaur sauropod eggs (attributable to et al., 2000), the largest extant “giant” species being about 232 mm Megaloolithus), although it has also yielded an articulated skeleton in SVL. The largest size ever achieved by a terrestrial lizard would tentatively referred to a lizard, fragmentary teeth of crocodiles and correspond to the extinct Varanus priscus (SVL >2000 mm), fol- bones of adult and juvenile dinosaurs (Lo pez-Martínez, 2000). The lowed by the extant Varanus komodoensis (SVL ~1500 mm), sizes putative lizard was interpreted as a potential nest raider (Lo  pez- according to Conrad et al. 2012. Note, however, that the fossil giant Martínez, 2000), but has never been described. It is, however, taxon is not included in the regression line because we do not have much smaller in size than the specimen described herein, sug- access to specimens for which both the mtV length and the SVL are gesting that these specimens do not belong to the same taxon. known. A SVL of ~581 mm probably situates the form from Basturs- Moreover, according to its size, MCD-8827 is more likely to repre- 1 as the largest terrestrial lizard from the European fossil record sent an example of nest raider lizard than the small skeleton. Ac- and contributes to our limited knowledge on the diversity and cording to Riera et al. (2009), the lithology found at Basturs-1 paleoecology of Iberian Upper Cretaceous lizards. corresponds to a medium to very coarse grain sandstone, and the As a final note, large sized Upper Cretaceous anguimorphs like interpreted paleoenvironment is of beach, barrier and delta. The the North American Palaeosaniwa canadensis and the Asian Aspro- nearby locality of Basturs Poble does not contain eggs, but it is saurus bibongriensis, Chianghsia nankangensis and Estesia mongol- extremely rich in hadrosaur bones and has occasionally yielded iensis have been all found close to dinosaur eggs (Gilmore, 1928; theropod dinosaur and crocodile remains. This site contains mixed Norell et al., 1992; Mo et al., 2012; Park et al., 2015), suggesting very fine-to coarse-grained sandstone, microconglomerates and they might represent nest raiders (Park et al., 2015). The locality of conglomerates interpreted as a meandering fluvial channel 11 ndez, A. Bolet, A. Torices et al. A. Cabezuelo Herna Cretaceous Research 131 (2022) 105094 environment. It is thus possible that changes in the recorded fauna References across these localities were indeed influenced by changes in the depositional setting and environment, and reflect true composi- Alifanov, V., 1993. Some peculiarities of the Cretaceous and Palaeogene lizard faunas of the Mongolian People's Republic. Kaupia. Darmst€ €ge zur Natur- adter Beitra tional differences. geschichte 3, 9e13. Alifanov, V.R., 2000. The fossil record of Cretaceous lizards from Mongolia. In: Benton, M.J., Shishkin, M.A., Unwin, D.M., Kurochkin, E.N. (Eds.), The Age of Dinosaurs in Russia and Mongolia. 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These elements (with the possible Bardet, N., Carmelo Corral, J., Pereda Suberbiola, X., 1999. Marine reptiles from the exception of the astragalocalcaneum) have been of limited help in uppermost Cretaceous of the Laneo quarry (Iberian Peninsula). Estudios del Museo de Ciencias Naturales de Alava  14, 373e380. characterising the different groups of squamates. Bardet, N., Cappetta, H., Pereda Suberbiola, X., Mouty, M., Al Maleh, A.K., Some characters of MCD-8827 (e.g. proximal head of the fifth Ahmad, A.M., Khrata, O., Gannoum, N., 2000. The marine vertebrate faunas from metatarsal with squarish contours, plantar tubercles and outer the Late Cretaceous phosphates of Syria. Geological Magazine 137, 269e290. process pretty developed in an ovoid-rounded shape, lateral Bardet, N., Pereda Suberbiola, X., Jalil, N.-E., 2003. A new mosasauroid (Squamata) from the Late Cretaceous (Turonian) of Morocco. 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A few other characters (e.g. absence of an enlarged Bardet, N., Martin, G., Carmelo Corral, J., Pereda Suberbiola, X., Astibia, H., 2013b. medial plantar tubercle occupying the majority of the articulation New mosasaurid teeth (Reptilia: Squamata) from the Maastrichtian of Albaina facet, fourth distal tarsal completely lied upon the third distal tarsal (Laneo quarry, Condado de Trevineo). Spanish Journal of Palaeontology 28, 69e78. and a hooking angle closer to 140 ), however, seem to support a Balsai, M.J., 2001. The phylogenetic position of Palaeosaniwa and the early evolution of the Platynotan (Varanoid) anguimorphs. Electronic Dissertations. University closer affinity of the specimen studied here to Varanus than to of Pennsylvania, pp. 1e278. Heloderma or Shinisaurus and, accordingly, it is tentatively assigned Bell Jr., G.L., Polcyn, M.J., 2005. Dallasaurus turneri, a new primitive mosasauroid to Varaniformes. This form is the largest terrestrial squamate so far from the Middle Turonian of Texas and comments on the phylogeny of Mosa- sauridae (Squamata). Netherlands Journal of Geosciences d Geologie en known from the European fossil record, and is among the largest Mijnbouw 84, 177e194. squamates from the worldwide Mesozoic record. Moreover, it Benton, M.J., 1985. Classification and phylogeny of the diapsid reptiles. Zoological represents an additional record of a large anguimorph associated to Journal of the Linnean Society 84, 97e164. Bhullar, B.-A.S., 2011. The Power and Utility of Morphological Characters In Sys- a dinosaur nesting site. A more precise identification is hampered tematics: A Fully Resolved Phylogeny of Xenosaurus and Its Fossil Relatives by the current limited knowledge of tarsus elements morphologies (Squamata: Anguimorpha). Bulletin of the Museum of Comparative Zoology in many extant groups and, particularly, for fossil forms. 160, 65e181. Bhullar, B.-A.S., Smith, K.T., 2008. Helodermatid Lizard from the Miocene of Florida, the Evolution of the Dentary in Helodermatidae, and Comments on Dentary Morphology in Varanoidea. Journal of Herpetology 42, 286e302. Acknowledgments Blain, H.-A., Canudo, J.-I., Cuenca-Besco s, G., Lo pez-Martínez, N., 2010. Amphibians and squamate reptiles from the latest Maastrichtian (Upper Cretaceous) of Blasi 2 (Huesca, Spain). Cretaceous Research 31, 433e446. This research has been funded by the Ministerio de Ciencia e Blanco, A., 2017. Vertebrate microfossil diversity from the Tremp Formation Innovacio n of the Spanish Government (PID2019-111488RB-I00). (Maastrichtian): Contributions to evolution of the Late Cretaceous terrestrial A.B. work is supported by a Juan de la Cierva Incorporacio n ecosystems from the northeastern Iberian Peninsula. PhD Thesis. Universitat Autonoma de Barcelona, pp. 29e330. Fellowship (IJC2018-037685-I, funded by Ministerio de Ciencia e Blanco, A., Me ndez, J.M., Marmi, J., 2015. The fossil record of the Uppermost Innovacio n of the Spanish Government). A.T. is supported by La Maastrichtian Reptile Sandstone (Tremp Formation, northeastern Iberian Rioja Government by “Convenio para la financiacio n de actividades Peninsula). Spanish Journal of Palaeontology 30, 147e160. Blanco, A., Bolet, A., Blain, H.-A., Marmi, J., 2016. Amphibians and squamates from de la Ca tedra Extraordinaria de Patrimonio Paleontolo gico” in the the Maastrichtian (Late Cretaceous) of north-eastern Iberia. Cretaceous Universidad de La Rioja. Support from the CERCA programme (ICP) Research 57, 624e638. from the Generalitat de Catalunya is acknowledged. Authors thank Bolet, A., 2017. First early Eocene lizards from Spain and a study of the composi- tional changes between late Mesozoic and early Cenozoic Iberian lizard as- M. Padilla (MACV), M. Calvo (MNCN), M. A. Brown, K. 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