Anguidae

Villa, Andrea & Delfino, Massimo, 2019, A comparative atlas of the skull osteology of European lizards (Reptilia: Squamata), Zoological Journal of the Linnean Society 187 (3), pp. 828-928 : 842-843

Anguidae ( Figs 5Y, Z , 6A–C, J, K )

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 ). 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 , 6A, C ). 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 ) than in Pseudopus apodus ( Fig. 6A ). 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 ). The occipital shield is small in Anguis gr. An. fragilis ( Fig. 5Y ) and large in Pseudopus apodus ( Fig. 6A ). 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 , 6A, C ). 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 ) and Pseudopus apodus with a shield that is distinctly longer than the area levis ( Fig. 6A ). 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 ), 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 ). 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 ). 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 ). In juveniles of Anguis and in Pseudopus apodus , the posterior portion of the wide fossa is visible in ventral view ( Fig. 6B ). 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 ). The carina is not developed posteriorly in Anguis gr. An. fragilis ( Fig. 5Y, Z ). 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 ), at the contact of the anterolateral and posterolateral ventral crests, but not in Anguis gr. An. fragilis ( Fig. 6J ). A wide and elliptical ( Anguis gr. An. fragilis ; Fig. 5Y, Z ) or circular ( Pseudopus apodus ; Fig. 6A, B ) parietal foramen is present in the middle of the table, even though sometimes it can be obliterated by the dermal ornamentation ( Fig. 6C ). 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 , 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.

Figures

Figure 5. Parietals – A–B, Laudakia stellio (MDHC 245), parietal in dorsal (A) and ventral (B) views. C–D, Chamaeleo chamaeleon (NHMW 611), parietal in dorsal (C) and ventral (D) views. E–F, Ac. erythrurus (UAM.R.ACVII), parietal in dorsal (E) and ventral (F) views. G–H, Lacerta schreiberi (UAM.R.S-6), parietal in dorsal (G) and ventral (H) views. I–J, Ophisops elegans (MDHC 281), parietal in dorsal (I) and ventral (J) views. K–L, Ti. lepidus (MDHC 216), parietal in dorsal (K) and ventral (L) views. M–N, Z. vivipara (UAM.R.Lv24), parietal in dorsal (M) and ventral (N) views. O–P, Ab. kitaibelii (MDHC 239), parietal in dorsal (O) and ventral (P) views. Q–R, Chalcides chalcides (MDHC 398), parietal in dorsal (Q) and ventral (R) views. S–T, Chalcides ocellatus (MDHC 250), parietal in dorsal (S) and ventral (T) views. U–V, Ophiomorus punctatissimus (MDHC 427), parietal in dorsal (U) and ventral (V) views.W–X, Tr. aurata (MDHC 280), parietal in dorsal (W) and ventral (X) views. Y–Z, Anguis gr. An. fragilis (MDHC 102), parietal in dorsal (Y) and ventral (Z) views. Abbreviations: al, area levis; alp, anterolateral process; as, anterior section of the anterolateral ventral crest; aspa, articulation surface with the processus ascendens of the supraoccipital; avc, anterolateral ventral crest; fps, frontoparietal shield; ips, interparietal

Figure 6. Parietals (continued) – A–B, Pseudopus apodus (MDHC 214), parietal in dorsal (A) and ventral (B) views (supratemporal processes are broken). C, Pseudopus apodus (PIMUZ A/III0975), parietal in dorsal view. D, Laudakia stellio (MDHC 245) in right lateral view. E, Chamaeleo chamaeleon (NHMW 611), parietal in right lateral view. F, Lacerta bilineata (MDHC 381), parietal in left lateral view. G, Chalcides ocellatus (MDHC 250), parietal in left lateral view. H, Ophiomorus punctatissimus (MDHC 427), parietal in left lateral view. I, Tr. aurata (MDHC 280), parietal in left lateral view. J, Anguis gr. An. fragilis (MDHC 102), parietal in left lateral view. K, Pseudopus apodus (MDHC 214), parietal in right lateral view (supratemporal processes are broken). Abbreviations: al, area levis; as, anterior section of the anterolateral ventral crest; aslf, articulation surface with the lappet of the frontal; ca, carina arcuata; ep, epipterygoid process; fps, frontoparietal shield; l, lappet; mc, median crest; pc, parietal crest; pfs, parietal fossa; ps, posterior section of the posterolateral ventral crest. Scale bars = 1 mm.

Figure 8. Premaxillae – A–C,Laudakia stellio (HUJ.OST-Z-424), premaxilla in anterior (A), left lateral (B), and posterior (C) views. D, Chamaeleo chamaeleon (NHMW 721), articulated premaxilla in anterior view. E–H, Ac.erythrurus (UAM.R.ACVII), premaxilla in anterior (E), posterior (F), left lateral (G) and ventral (H) views. I–L, I. monticola monticola (UAM.R.Lm77), premaxilla in anterior (I), posterior (J), right lateral (K) and dorsal (L) views. M–P, Lacerta bilineata (MDHC 15), premaxilla in anterior (M), posterior (N), left lateral (O) and dorsal (P) views. Q–T, Po. waglerianus (MDHC 390), premaxilla in anterior (Q), posterior (R), right lateral (S) and dorsal (T) views. U, Z. vivipara (UAM.R.Lv24), premaxilla in posterior view. V–Y, Chalcides chalcides (MDHC 94), left premaxilla in anterior (V), posterior (W), lateral (X) and dorsal (Y) views.Abbreviations: am, alveolar margin; anp, ascending nasal process; ap, alveolar plate; flc, foramen of the longitudinal canal; ip, incisive process; pp, palatal process; sc, septonasal crest. Scale bars = 1 mm.

Figure 9. Premaxillae (continued) – A–D, Chalcides ocellatus (MDHC 250), right premaxilla in anterior (A), posterior (B), dorsal (C) and lateral (D) views. E–H, Anguis gr. An. fragilis (MDHC 102), premaxilla in anterior (E), posterior (F), left lateral (G) and ventral (H) views. I–J, Pseudopus apodus (MDHC 215), premaxilla in anterior (I) and posterior (J) views (the right side of the alveolar plate is broken). Abbreviations: ip, incisive process; mp, maxillary process; n, notch; pp, palatal process; sc, septonasal crest; vp, vomerine process. Scale bars = 1 mm.