Podarcis sp.

Marquina-Blasco, Rafael, Fagoaga, Ana, Crespo, Vicente D., Martínez-Ortí, Alberto, Bailon, Salvador, Sánchez-Marco, Antonio, Gracia-Monferrer, Daniel, Santisteban, Carlos de & Ruiz-Sánchez, Francisco Javier, 2023, Squamates, rodents, and birds from Holocene deposits of the Illa Grossa Island (Columbretes Islands, Castellón, Spain): an unexpected diverse assemblage, Comptes Rendus Palevol 22 (18), pp. 409-438 : 416-417

cf. Podarcis sp.

( Fig. 3 I-M)

MATERIAL EXAMINED. — 4 premaxillae ( COLT-15, 16 and 43 ); 4 left maxillae ( COLT-18, 19 and 39 ); 2 right maxillae ( COLT-17 ); 2 left pterygoids ( COLT-21 and 22 ); 1 dorsal vertebra ( COLT-40 ); 1 possible sacral vertebra ( COLT-53 ); 2 caudal vertebrae ( COLT-41 ); 1 centrum of caudal vertebra ( COLT-48 ); 1 right coxal ( COLT-42 ); 2 left humeri ( COLT-45 and 57 ); 1 right humerus ( COLT-46 ) .

DESCRIPTION

The premaxillae of this species are represented in the Columbretes Islands by four small-sized remains, with an average with of the premaxillary shelf of 1.23 mm (n = 3; σ = 0.13). The posterodorsal process is thin and has parallel lateral margins ( Fig. 3I). The most complete specimen (COLT-43) has seven dental positions, but only three teeth are present. These are pleurodont, isodont, cylindrical, and monocuspid with a blunt apex. COLT-16 shows the distal end of the posterodorsal process slightly expanded ( Fig. 3J). The nasal foramina are present at the base of the posterodorsal process. In posterior view, this process has a well-defined medial crest.

The maxilla bears pleurodont, isodont, cylindrical, mono or bicuspid teeth with a blunt apex. In dorsal view, the remains have a wide palatal shelf with a large superior dental foramen. The anterior margin of the maxilla has short anteromedial and anterolateral processes. The two processes are similar in size; however, the anterolateral process seems to be slightly larger than the anteromedial one. The notch formed on the anterior concavity between both processes is shallow. A wide vomeronasal foramen is located in the basis of the anterior margin of the dorsal process. In lingual view, the anteromedial process does not show any lappet. However, in COLT-39 the anteromedial process, although broken, seems to be elevated and, probably, formed a lappet. It is impossible to evaluate the degree of development of the eroded prefrontal process. The posterior process is short and with a step on its dorsal margin ( Fig. 3K). In labial view, the surface of the maxilla is smooth and shows three labial foramina.

The dentaries are fragmentary ( Fig. 3L). The recovered remains bear pleurodont, isodont, cylindrical, bi- and monocuspid teeth, with a more or less pointed principal cuspid. In lingual view, the Meckelian groove is open and the subdental shelf is arched.

The vertebrae are procoelous and longer than wide. In dorsal view, they show a marked interzygapophyseal constriction. In the foremost part, the remains show a rudimentary zygosphene-zygantrum articulation, sensu Hoffstetter (1969) and Hoffstetter & Gasc (1969). The neural spine runs along the entire length of the neural arch, except its first quarter. The neural arch terminates in a point, which does not overtake the postzygapophysis. In lateral view, the neural spine is low. The vertebra has an oval-shaped synapophysis, which is slightly anteroposteriorly projected. The ventral margin of the centrum is convex. In ventral view, the centrum is subtriangular in shape with its anterior part wider than the posterior one. The haemal keel is absent. A pair of small not well-defined subcentral foramina is present. In anterior and posterior view, the condyle and the cotyle are small and have a subcircular shape.COLT-48 consists in a centrum of a procoelous caudal vertebra, slightly wider than longer with well-developed and dorsoventrally flattened transverse processes.

The coxal is a large elongated triradiate compound bone ( Fig. 3M). It is formed by the complete fusion of the ilium, ischium, and pubis, without any trace of suture line. In the posterior region of the ilium, a hooked preacetabular spine is dorsally projected. The coxal does not show any dorsal crest. The acetabulum is oval and large. The pubis is broken. Although the ischium is broken, it seems to be large and wide. It forms a posterior angle of about 90° with the ilium.

The recovered humeri have only the distal end preserved. The epiphysis is wider than the diaphysis. In ventral view, it shows a deep radioulnar fossa. The radial condyle is oval in shape and transversely compressed, whereas the ulnar condyle is slightly larger and rounded. The ectepicondyle is not well differentiated. The entepicondyle is reduced. The entepicondylar foramen is large.

REMARKS

The fossils described here show typical traits of Lacertidae : fused premaxilla with a slender posterodorsal process; pleurodont, isodont and mono or bicuspids teeth; ventral edge of the dentary concave in lingual view; Meckelian groove of the dentary open along its whole length in lingual view; procoelous vertebra with the centrum transversally convex and the neural spine not exceeding the posterior limit of the postzygapophysis; coxal with preacetabular spine but no dorsal crest, humerus with a laterally flattened radial condyle, rounded ulnar condyle, and the presence of an ectepicondylar foramen ( Bailon 1991; Barahona 1996; Russell & Bauer 2008). Although the osteology of the lacertids is poorly studied, some taxonomic ascription can be tried. Thus, the presence of a step in the posterior process of the maxilla is a characteristic reported byBarahona & Barbadillo (1997) and Villa & Delfino (2019a) for the lacertid genera Iberolacerta Arribas, 1997 , Lacerta Linnaeus, 1758 , and Podarcis . Regarding the premaxilla, the parallel position of lateral margins of the posterodorsal process and the number of dental positions exclude some lacertid species, reducing the options to Podarcis , Iberolacerta, Psammodromus Fitzinger, 1826 and Acanthodactylus Wiegmann, 1834 ( Barahona & Barbadillo 1997). The last two can be discarded due to the absence of a step in the posterior process of the maxilla ( Barahona & Barbadillo 1997; Villa & Delfino 2019a). The mean size of the premaxilla shelf is included in the range of the Podarcis species provided by Barahona (1996), except for Podarcis bocagei (Seoane, 1884) , considered as Podarcis bocagei bocagei in the refereed work, and Iberolacerta bonnali (Lantz, 1927) , in which sizes are larger than those recorded for the COLT lacertid premaxilla. On the other hand, the number of premaxillary teeth (7) restrains the options to Podarcis muralis (Laurenti, 1768) , P. bocagei , Podarcis hispanica sensu lato (Steindachner, 1870) and Iberolacerta bonnali (Lantz, 1927) ( Barahona & Barbadillo 1997) . Following biogeographic criteria, the presence of a species of Iberolacerta seems unlikely because these lacertids are almost entirely confined to small widely separated mountain areas (e.g. I. bonnali only inhabited the Central Pyrenees) and they tend to be taxa adapted to cold environments ( Ortega et al. 2016). Thus, all these characteristics permit an attribution of the COLT fossils to cf. Podarcis sp.

The fossil record of lacertids is known in the larger Mediterranean islands ( Bailon 2004). The insular record of the genus Podarcis is limited to Crete, Sicily, Sardinia, Corsica, Mallorca, Ibiza, and Menorca ( Bailon 2004; Villa & Delfino 2019b). Several works ( Bover et al. 2014; Rodríguez et al. 2017; Spilani et al. 2019) proposed that the ancestors of the current Podarcis species that inhabit these islands reached them via land bridges. However, the populations of Podarcis siculus (Rafinesque-Schmaltz, 1810) , present in Menorca, Sardinia and Corsica, have been introduced by humans in historical times ( Silva-Rocha et al. 2018).

CURRENT ECOLOGY

Podarcis is a circummediterranean genus that is widespread in Southern Europe, the Anatolian Peninsula and Northern Africa (Spreybroeck et al. 2016). At least, 12 species are endemic of the Mediterranean islands, especially in the Aegean Sea (Spreybroeck et al. 2020). At present, the Columbretes archipelago is inhabited by Podarcis liolepis atratus (Boscá, 1916) , until recently considered as an endemic insular subspecies ( Ruiz-Sánchez et al. 2019 and references therein). This lizard is present in all islands and islets of the Columbretes, except in the Ferrera group ( Castilla et al. 1998a). The absence of the species in Ferrera is not understood, since this island include potential habitats for this lizard. The presence of fossils of a Wall Lizard ( Podarcis sp. ), or related taxa, in a palaeontological context confirms the ancient occupation of the Columbretes Islands by this taxon. The open taxonomical attribution proposed for the lacertid fossils does not allow further inferences about the palaeoecological context during the formation of the site.