Anguidae

Anguidae View in CoL View at ENA ( Figs 5Y, Z View Figure 5 , 6A–C, J, K View Figure 6 )

The parietal of anguids is unpaired and presents a rectangular table that is longer than it is wide. The anterior margin is slightly irregular, with small interdigitations in adults, whereas the lateral ones are roughly straight. In ventral view, a small articulation surface for the ventral lappet of the posterolateral process of the frontal is visible near each anterolateral corner of the table, and a similar small and anteriorly developed ventral lappet is present medially to this surface. The anterolateral processes are poorly developed. The long supratemporal processes are strongly medially expanded in their proximal-half, but they narrow distally, ending with a moderately robust and posteriorly rounded distal end. The ventral curve is little developed ( Fig. 6J, K View Figure 6 ). A well-developed dermal ornamentation is present on the dorsal surface of the table, and the frontoparietal, interparietal, lateral and occipital shields are recognizable ( Figs 5Y View Figure 5 , 6A, C View Figure 6 ). The interparietal shield is large and reaches the anterior margin of the table, limiting the frontoparietal ones to the anterolateral corners of the bone. On the anterior margin, the interparietal shield is distinctly wider in Anguis gr. An. fragilis ( Fig. 5Y View Figure 5 ) than in Pseudopus apodus ( Fig. 6A View Figure 6 ). Linked to this difference in width, the anterior end of each groove separating the interparietal shield from the related frontoparietal shield is directed towards the anterolateral corner of the ornamented surface in Anguis gr. An. fragilis , whereas it is located more medially in Pseudopus apodus [see also Klembara et al. (2017) and Klembara & Rummel (2018)]. Moreover, the dermal ornamentation in Anguis gr. An. fragilis is usually less marked on the frontoparietal shields compared to the rest of the table ( Fig. 5Y View Figure 5 ). The occipital shield is small in Anguis gr. An. fragilis ( Fig. 5Y View Figure 5 ) and large in Pseudopus apodus ( Fig. 6A View Figure 6 ). Posteriorly, the ornamentation does not reach the posterior margin of the parietal table, because of the presence of a large and smooth area levis ( Figs 5Y View Figure 5 , 6A, C View Figure 6 ). According to Klembara (2012), Klembara et al. (2017) and Klembara & Rummel (2018), the area levis is shorter than the occipital shield in Anguis , whereas it is as long as the shield in Pseudopus . However, a certain degree of variation of this feature is evident based our specimens, which include Anguis gr. An. fragilis with an occipital shield that is as long as the area levis ( Fig. 5Z View Figure 5 ) and Pseudopus apodus with a shield that is distinctly longer than the area levis ( Fig. 6A View Figure 6 ). As in lacertids and scincids, the ventral crests are visible on the otherwise smooth ventral surface. Anterolateral and posterolateral crests contact each other in both Anguis gr. An. fragilis and Pseudopus , whereas the contact between the anterolateral and the medial ones is only present in the latter genus ( Fig. 6B View Figure 6 ), because in Anguis gr. An. fragilis the posterior ends of the anterolateral ventral crests is shifted towards the posterior margin of the bone ( Fig. 5Z View Figure 5 ). The contact of the anterolateral ventral crest with the medial ventral crest in Pseudopus apodus splits the margin of the parietal fossa into two sections, respectively called crista juxtafovealis (anterior to the contact) and crista postfovealis (posterior to the contact) in Klembara et al. (2010). Due to the posterior shifting of the posterior end of the anterolateral ventral crest, the crista postfovealis is not present in Anguis gr. An. fragilis . The medial ventral crest [lamina medialis in Klembara et al. (2010)] is moderately wide, the posterolateral ventral crests [ventrolateral ridge in Klembara et al. (2010)] can be robust or sharp and the anterolateral ventral crests [cristae cranii parietalis in Klembara et al. (2010)] are sharp. The latter are subdivided in two sections: a well-developed anterior one and a low posterior one. The parietal table of Pseudopus apodus extends laterally beyond the anterolateral ventral crests, forming a wide facies muscularis on each side of the bone. This facies is not developed in Anguis gr. An. fragilis . A narrow and smooth ventrolateral surface located laterally to the posterolateral ventral crest versus a crest that marks the lateral margin of the supratemporal process is commonly used to distinguish Pseudopus from Anguis (see, for example: Klembara et al., 2010, 2017; Klembara, 2012; Klembara & Rummel, 2018). However, it seems that, at least among the herein-studied specimens, Anguis gr. An. fragilis can also display such a narrow surface in some cases ( Fig. 5Z View Figure 5 ). In adults of Anguis gr. An. fragilis , the medial ventral crest completely covers the parietal fossa and, therefore, only the wide and U-shaped parietal notch is visible posteriorly to it ( Fig. 5Z View Figure 5 ). In juveniles of Anguis and in Pseudopus apodus , the posterior portion of the wide fossa is visible in ventral view ( Fig. 6B View Figure 6 ). Moreover, in the latter species, a carina arcuata extends posteriorly covering most of the notch, which appears only as a wide but shallow concavity in dorsal view ( Fig. 6A View Figure 6 ). The carina is not developed posteriorly in Anguis gr. An. fragilis ( Fig. 5Y, Z View Figure 5 ). The development of the parietal notch undergoes ontogenetic variation in Anguis gr. An. fragilis , because its depth seems to increase during growth. A little or moderately developed epipterygoid process is present in Pseudopus apodus ( Fig. 6K View Figure 6 ), at the contact of the anterolateral and posterolateral ventral crests, but not in Anguis gr. An. fragilis ( Fig. 6J View Figure 6 ). A wide and elliptical ( Anguis gr. An. fragilis ; Fig. 5Y, Z View Figure 5 ) or circular ( Pseudopus apodus ; Fig. 6A, B View Figure 6 ) parietal foramen is present in the middle of the table, even though sometimes it can be obliterated by the dermal ornamentation ( Fig. 6C View Figure 6 ). Maximum length of the parietal varies from 3.2 mm to 5.8 mm in Anguis gr. An. fragilis and from 11 mm to 11.5 mm in Pseudopus apodus , whereas its maximum width goes from 3 mm to 4.4 mm in the former and from 10.5 mm to 11 mm in the latter.

PREMAXILLA

The unpaired premaxilla ( Figs 8 View Figure 8 , 9 View Figure 9 ) is composed of a ventral alveolar plate and an ascending nasal process that projects posterodorsally from the middle portion of the alveolar plate. Posteriorly, the alveolar plate extends into the two thin and triangular palatal processes, divided medially by a wide notch. Between the bases of these processes, the small and ventrally directed incisive process is present. The teeth are supported by the alveolar margin of the alveolar plate. By the junction between the ascending nasal process and the alveolar plate, the foramina of the longitudinal canals are visible by the sides of the process. A septonasal crest runs medially along the posterior surface of the nasal process.