Chalcides bedriagai ( Boscá, 1880 )

Marquina-Blasco, Rafael, Fagoaga, Ana, Crespo, Vicente D., Martínez-Ortí, Alberto, Bailon, Salvador, Sánchez-Marco, Antonio & Gracia-Monferrer, Daniel, 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 : 414-416

Chalcides bedriagai ( Boscá, 1880)

( Fig. 3 A-H)

Gongylus ocellatus bedriagai Boscá, 1880: 50 (original description of the species, holotype designated).

Chalcides bedriagae – Boulenger 1887: 402 (current taxonomy established). — Salvador 1998: 152 (lectotype designed).

MATERIAL EXAMINED. — 1 right premaxilla (COLT-4); 4 right maxillae (COLT-7 and 8); 2 left maxillae (COLT-56); 1 left postfrontal (COLT-23); 2 right pterygoids (COLT-20 and 24); 3 right dentaries (COLT-1 and 9); 4 left dentaries (COLT-3 and 11); 11 dorsal vertebrae (COLT-12 and 13); 4 caudal vertebrae (COLT-14); 1 right coxal (COLT-45); 1 right femur (COLT-47).

DESCRIPTION

The preserved premaxilla (COLT-4) is the left one ( Fig. 3A). This remain has three dental positions, but only two teeth are present. These are pleurodont, isodont, cylindrical, and monocuspid with a blunt apex. In frontal view, the posterodorsal process is short and leaf-shaped. No foramen is observable in the bone.

COLT-7 is the distal half of a right maxilla ( Fig. 3B). Thus, only the posterior and prefrontal processes, although partially broken, are preserved. In labial view, the prefrontal process seems to be subpentagonal, with an anterior margin broken, a dorsal margin roughly subdivided in anterodorsal and posterolateral portions and a sigmoidal posterior margin. A dorsal corner and a posterodorsal corner are clearly visible. The labial surface of the bone is smooth and only one labial foramen is visible; however, the surface is highly damaged so an additional foramen might also be present. In lingual view, the maxilla bears pleurodont, isodont, cylindrical, and monocuspid teeth with a more or less blunt apex. The teeth show a more or less visible ornamentation, with delicate vertical striation limited ventrally by a transverse groove. The supradental shelf is arched and partially broken at the palatine process.

The postfrontal is Y-shaped ( Fig. 3C). The anteromedial and anterolateral processes are short and pointed. Both processes have similar size; however, the anterolateral process is more robust than the anteromedial one. In ventral view, the ventral surface between these two processes is concave. On the medial margin, the insertion surface with the frontal and parietal is well marked, while on the lateral margin, the impression with the postorbital is less deep.

COLT-20 is the preserved anterior part of a right pterygoid ( Fig. 3D). The quadrate (posterior), transverse (anterolateral) and palatine (anteromedial) processes are partially broken. However, the latter is subrectangular and shows a thicker area in the middle of its platform. The transverse process is subtriangular and has well marked impressions of the ectopterygoid on its dorsal surface. The pterygoid recess is deep and U-shaped. The basis of the quadrate process is broken, for this reason it is not possible to describe it. In lateral view, the transverse process presents a wide and short insertion surface of the pterygoideus muscle. No pterygoid teeth are present.

The dentaries bear pleurodont, isodonts, and cylindrical teeth with flattened or slightly concave lingual surfaces of the crowns and apices oriented in lingual direction ( Fig. 3E). In labial view, the teeth appear monocuspid (a slightly pointed or blunt labial cuspid), but in lingual view, underneath the labial cuspid, a smaller lingual cuspid may be present. The antrum intercristatum is a generally well-marked groove located on one side and on the other, between these two cuspids. Every tooth apex shows a transversal groove, only some teeth show a vertical striation. The most complete dentaries (COLT-1 and COLT-3) are characterized by the presence of 17 dental positions ( Fig. 3E). The width/height ratio for all the teeth equals 0.3 (n = 31; δ = 0.07). The coronoid process is subtriangular, straight and posterodorsally projected. In labial view, this process does not show any impression of the coronoid on the wall of the dentary. The studied dentaries present four lingual foramina. In lingual view, the Meckelian groove is open in its whole length and narrower between the eighthninth dental position and the anterior end of the tooth row. The subdental shelf is slightly arched and the ventral margin of the dentary is straight.

The vertebrae are procoelous and longer than wide (vertebral centrum length (CL), CLmed = 1.94 mm; n= 5; σ = 0.22; CLmin = 1.69 mm; CLmax = 2.23 mm; minimum width of the neural arch, measured at the maximum intrazygapohyseal constriction (NAW), NAWmed = 0.98 mm; n = 4; σ = 0.08; NAWmin = 0.86 mm; NAWmax = 1.05 mm). In dorsal view, they show a few marked interzygapophyseal constrictions ( Fig. 3F). The neural arch shows a rudimentary zygosphene-zygantrum articulation, sensu Hoffstetter (1969) and Hoffstetter & Gasc (1969), with two shorts lateral facets (zygosphene) but with a barely outlined posterior zygantrum. The neural spine runs along the entire length of the neural arch, finishing in a point that overtakes the posterior end of the postzygapophysis. In lateral view, the neural spine is low. The synapophyses are oval-shaped and slightly projected anteroposteriorly. In ventral view, the centrum is subcylindrical with its anterior part slightly wider than the posterior one. It shows neither haemal keel nor foramen, except in the case of one vertebra stored under the number COLT-13, which presents a pair of slightly marked large subcentral foramina. In anterior and posterior view, the condyle and cotyle are dorsoventrally flattened. COLT-14 includes two vertebrae, which have a pair of dorsoventrally flattened transversal processes typical of caudal vertebrae ( Bailon 1991).

COLT-45 is the anterior edge of a coxal, a large elongated bone ( Fig. 3H). In lateral view, on the ilium the preacetabular spine and dorsal crest are absent. The acetabulum is rounded.

Only the proximal end of the femur is preserved. It shows a well-developed, ventrally expanded femoral condyle. The internal trochanter is small and is not well defined. Both structures are separated by a large and deep intertrochanteric fossa in ventral view.

REMARKS

The traits described on the material (unfused premaxilla, morphology of the teeth, straight ventral end of the dentaries, open Meckelian groove, presence of a thicker area in the palatine process of the pterygoid, vertebrae with the end of the neural spine overtaking the posterior of the postzygapophysis, and absence of the preacetabular spine and dorsal crest in the coxal) are consistent with the genus Chalcides ( Barbadillo 1989; Bailon 1991; Caputo et al. 1995; Blain 2009; Villa & Delfino 2019a; Čerňanský et al. 2020). At present, there are three species of that genus in the Iberian Peninsula, the autochthonous Chalcides striatus (Cuvier, 1829) and Chalcides bedriagai , and the introduced Chalcides ocellatus Forsskal, 1775 ( Bisbal-Chinesta et al. 2020). In the latter species, teeth are robust with enlarged crowns ( Kosma 2004; Villa & Delfino 2019a). This morphology differs strongly from other members of the genus Chalcides ( Kosma 2004) . As we describe above, the COLT fossils do not show these traits on the teeth. Their morphology and width/high proportion do not differ from those of the modern species Chalcides bedriagai , which is characterized by 15 to 18 dental positions and a width/height ratio of 0.3 ( Barbadillo 1989; Caputo 2004); in contrast to C. striatus , which is characterized by 18 to 21 dental positions ( Caputo 2004) and a tooth width/height ratio of 0.22 ( López-Ruiz et al. 2002).

The fossil record of the genus Chalcides in the Mediterranean islands is scarce. In this sense, cf. Chalcides has been reported from the late Miocene/early Pliocene of Menorca ( Bover et al. 2014) and indeterminate species of the genus had been reported from the Pleistocene of Menorca ( Estes 1983), and Mallorca ( Holman 1998). Skinks are highly capable of transmarine migration, as shown by the diversification of the genus Chalcides in the Canary Islands. However, in the case of the Balearic Islands sites, it has been proposed that Chalcides colonized the archipelago during the Messinian Salinity Crisis (MSC), when these islands were connected to the mainland ( Carranza et al. 2008). A similar scenario was proposed for the origin of the endemic herpetofauna of the Balearic Islands ( Pinya & Carretero 2011), and the spread of Chalcides bedriagai in the Iberian Peninsula ( Carranza et al. 2008). The MSC event had a strong influence in the Mediterranean herpetofauna (e.g. Georgialis et al. 2019a). Currently, C. bedriagai inhabits numerous islands close to both the Atlantic and Mediterranean coasts of the Iberian Peninsula ( Pollo 2015; and references in Ruiz-Sánchez et al. 2019).

ECOLOGY

Chalcides bedriagai is an Iberian endemic species localized throughout the Iberian Peninsula, except its northermost area. The distribution range of this taxon is included into the Mediterranean bioclimatic region, except for some localities of northwestern Iberia; although C. bedriagai always occupies thermal areas or Mediterranean-like environments. Chalcides bedriagai frequents a wide variety of habitats, which are mainly characterized by sandy or earthy substrate with an abundance of shelters (rocks, roots, leaves and shrubs) and high sun exposure, which constitutes a limiting factor of their presence ( Pollo 2015).