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 : 851-852

Anguidae ( Fig. 12M–P, V )

In European anguids, both anteromedial and anterolateral processes are pointed and well developed, defining a very deep and U-shaped anterior concavity that is also moderately narrow in dorsal view ( Fig. 12V ). The two processes are slender and roughly similar in size in Anguis gr. An. fragilis , but the anteromedial process is slightly shorter than the anterolateral one in Pseudopus apodus . A well-developed lappet is present on the dorsal surface of the anteromedial process. In Anguis gr. An. fragilis , this lappet projects anteriorly beyond the end of the process with a pointed tip and bends slightly in medial direction ( Fig. 12V ). The posterior process is long, slender and pointed in lateral view, lacking any step. The vomeronasal foramen is small (very small in Pseudopus apodus ) and opens in a shallow anteriorly concave area, bordered laterally and medially by two low ridges. The superior dental foramen is wide and continues posteriorly in a wide groove that runs along the dorsal surface of the posterior process. Teeth are large (maximum size is reached in the middle of the tooth row in Anguis gr. An. fragilis and by its posterior end in Pseudopus apodus ) and subpleurodont, lacking only on the posterior end of the maxilla. In Anguis gr. An. fragilis , they are monocuspid, trenchant, well-spaced and distinctly posterolingually bent by their tip ( Fig. 12M, N ). Maxillae of Pseudopus apodus have two different tooth morphologies: anteriorly, they have monocuspid, cylindrical and slightly robust teeth, provided with a pointed and not curved tip, whereas on the posterior end there are very large, cylindrical and stout teeth, provided with a blunt and rounded crown ( Fig. 12O, P ). Teeth of Pseudopus apodus are closely spaced and increase gradually in size posteriorly, but the last ones are smaller than the preceding ones. Striae are not present in Anguis gr. An. fragilis , but visible on both the lingual and the labial sides in Pseudopus apodus . The facial process is subtrapezoidal in lateral view, with a slightly convex dorsal margin and slightly concave anterior and posterior margins; the latter is almost vertical in Anguis gr. An. fragilis ( Fig. 12M, N ) and slightly oblique in Pseudopus apodus ( Fig. 12O, P ). The width of the process is smaller than half the length of the bone in Anguis gr. An. fragilis and roughly half the length in Pseudopus apodus . Both its anterodorsal and posterodorsal corners are rounded and a variable number of small foramina can be present near the former one. No dermal ornamentation is present on the lateral surface of the facial process in Anguis gr. An. fragilis ( Fig. 12M ), whereas a very light one is visible in Pseudopus apodus ( Fig. 12O ). The medial surface has a thickened area on the anterior margin and a low (sometimes more distinct in Anguis gr. An. fragilis ) arched ridge, similar to the one present in lacertids and scincids. The maximum length of the alveolar border goes from 3.3 mm to 7 mm in Anguis gr. An. fragilis and from 12.5 mm to 16.6 mm in Pseudopus apodus , whereas the number of tooth positions is nine in Anguis gr. An. fragilis and goes from nine to 14 in Pseudopus apodus . Three or four ventrolateral foramina are present in Anguis gr. An. fragilis , three, four or five in Pseudopus apodus .

PREFRONTAL

The paired prefrontal ( Fig. 14 ) has an anteriorly concave body, named the orbitonasal flange. The large and pointed dorsal process starts from the medial side of the dorsal margin of the flange, extending in the posterodorsal direction. The laminar anterodorsal process develops in anterior direction from the orbitonasal flange and a posteroventral process develops ventrolaterally from its ventrolateral corner. A small posterolaterally directed projection is present at the tip of the posteroventral process. A wide notch of the lacrimal foramen is located between the anterodorsal and the posteroventral processes.

Figures

Figure 12. Maxillae (continued) – A–B, Z. vivipara (UAM.R.Lv24), left maxilla in lateral (A) and medial (B) views. C–D, Ab. kitaibelii (MDHC 239), left maxilla in lateral (C) and medial (D) views. E–F, Chalcides chalcides (MDHC 398), right maxilla in lateral (E) and medial (F) views. G–H, Chalcides ocellatus (MDHC 250), right maxilla in lateral (G) and medial (H) views. I–J, Ophiomorus punctatissimus (MDHC 427), left maxilla in lateral (I) and medial (J) views. K–L, Tr. aurata (MDHC 280), right maxilla in lateral (K) and medial (L) views. M–N, Anguis gr.An. fragilis (MDHC 102), right maxilla in lateral (M) and medial (N) views. O–P, Pseudopus apodus (MDHC 215), left maxilla in lateral (O) and medial (P) views (the anterior tip of the anteromedial process is broken and there is a pathologically-growth tooth). Q, Ac. erythrurus (UAM.R.ACVII), left maxilla in dorsal view. R, Lacerta bilineata (MDHC 381), right maxilla in dorsal view. S, Chalcides chalcides (MDHC 398), right maxilla in medial view.T, Chalcides ocellatus (MDHC 250), right maxilla in dorsal view. U, Ophiomorus punctatissimus

Figure 14. Prefrontals – A–B, Laudakia stellio (HUJ.OST-Z-5), right prefrontal in dorsal (A) and dorsolateral (B) views. C, Chamaeleo chamaeleon (MNHN 2002–24), right prefrontal in posterior view. D–E, Chamaeleo chamaeleon (NHMW 611), left prefrontal in dorsal (D) and medial (E) views. F–H, Lacerta bilineata (MDHC 381), left prefrontal in dorsal (F), lateral (G) and posterior (H) views. I–K, Ophisops elegans (MDHC 281), right prefrontal in dorsal (I), posterior (J) and lateral (K) views. L–N, Ti. lepidus (MDHC 216), left prefrontal in dorsal (L), posterior (M) and lateral (N) views. O–Q, Ab. kitaibelii (MDHC 239), right prefrontal in dorsal (O), posterior (P) and lateral (Q) views. R–T, Tr. aurata (MDHC 280), left prefrontal in dorsal (R), posterior (S) and lateral (T) views. U–W, Anguis gr. An. fragilis (MDHC 102), left prefrontal in dorsal (U), posterior (V) and lateral (W) views. X–Z, Pseudopus apodus (MDHC 214), left prefrontal in dorsal (X), posterior (Y) and lateral (Z) views. Abbreviations: adp, anterodorsal process; dp, dorsal process; n, notch of the lacrimal foramen; ofp, orbitonasal flange projection; onf, orbitonasal flange; pc, palpebral crest; pj, projection; pvp, posteroventral process; t, tubercle. Scale bars = 1 mm.