Lacertidae

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 : 901

Lacertidae ( Figs 49E–H , 50G–J , 51B )

The angular of lacertids ( Fig. 49E–H ) is unfused and dorsoventrally enlarged. Its anterior end is narrower than the posterior one, which is lobe-shaped (sometimes forked, e.g. Po. bocagei UAM.R.PB 48 and Psammodromus algirus UAM.R.Ps 9; Fig. 49E ). A moderately developed angular ridge is present on the medial surface, starting roughly in the middle of the ventral margin and running anterodorsally up to the tip of the anterior end. Ventrally to the ridge, the bone is thickened. The posterior alveolar foramen pierces the angular with a dorsomedial to ventrolateral direction ( Fig. 49H ). The lateral surface is smooth, except for the articulation surface with the dentary, which covers its anterior-half ( Fig. 49E, F ). The other bones fuse to form a compound bone ( Figs 50G–J , 51B ) that can be separated in two portions in juveniles. The articular condyle is subquadrangular in dorsal view and rather flattened. A stocky tubercle develops in the medial direction from its anteromedial corner ( Fig. 51B ). The retroarticular process is straight and subtriangular in medial view, given that it narrows posteriorly. Its posterior end is truncated. A well-developed tympanic ridge is visible on its medial surface, running longitudinally from the posteroventral corner of the articular condyle to the posterior end of the process. This ridge marks the ventral margin of the concave portion of the process, whereas ventrally to it there is a ridge-like ventral expansion. The expansion is well developed in Ac. erythrurus and E. arguta , giving a curved ventral margin to the compound bone of these species ( Fig. 50G ). In other European lacertids, the margin is usually straight in medial view ( Fig. 50H, I ), but a strong ventral development is visible also in both compound bones of MRAC 91-077-R-76 ( Fig. 50J ) and in the left one of NHMW 663 ( Fig. 52 ), both large individuals of Lacerta viridis , suggesting some degree of individual variation maybe linked to size in this species (but some kind of pathological condition cannot be excluded a priori). The angular process is not present. The lateral surface of the compound bone is smooth, except for the presence of the wide articulation surface with the angular ( Fig. 50I ). In Lacerta agilis , Lacerta bilineata , Lacerta viridis and Ti. lepidus , a distinct and rather sharp longitudinal ridge runs dorsally to the articulation surface ( Fig. 50I ). This ridge undergoes a significant degree of individual variation, which might either be linked to the age or the size of the animal. A similar ridge is also present in some large specimen of Al. nigropunctatus (MDHC 243), Po. muralis (MDHC 6), Po. siculus (MDHC 91 and 229) and Po. tiliguerta (a poorly developed one in both the here studied specimens). The adductor fossa is very wide.

Figures

Figure 49. Angulars. A–B, Laudakia stellio (HUJ.OST-Z-423), left angular in dorsal (A) and medial (B) views. C–D, Chamaeleo chamaeleon (HUJ.OST-Z-425), right angular in dorsal (C) and medial (B) views. E, Psammodromus algirus (UAM.R.Ps9), left angular in lateral view. F–H, Ti. lepidus (MDHC 216), left angular in lateral (F), medial (G) and dorsal (H) views. I–J, Chalcides ocellatus (MDHC 250), left angular in lateral (I) and medial (J) views. K–L, Anguis gr.An. fragilis (MDHC 102), right angular in lateral (K) and medial (L) views. M–N, Pseudopus apodus (MDHC 214), right angular in lateral (M) and medial (N) views. Abbreviations: ar, angular ridge; asd, articulation surface for the dentary; paf, posterior alveolar foramen. Scale bars = 1 mm.

Figure 50. Compound bones.A–B, Laudakia stellio (MDHC 245), right surangular in medial (A) and lateral (B) views. C–D, Laudakia stellio (HUJ.OST-Z-424), fused left prearticular and articular in medial (C) and lateral (D) views. E–F, Chamaeleo chamaeleon (NHMW 611), right compound bone in medial (E) and lateral (F) views. G, Ac. erythrurus (UAM.R.ACVII), left compound bone in medial view. H–I, Lacerta agilis (MDHC 176), left compound bone in medial (H) and lateral (I) views. J, Lacerta viridis (MRAC 91-077-R-76), right compound bone in medial view. K–L, Ab. kitaibelii (MDHC 239), left compound bone in medial (K) and lateral (L) views. M–N, Chalcides ocellatus (MDHC 250), right compound bone in medial (M) and lateral (N) views. O–P, Ophiomorus punctatissimus (MDHC 427), right compound bone in medial (O) and lateral (P) views. Q–R, Tr. aurata (MDHC 280), left compound bone in medial (Q) and lateral (R) views. S–T, Anguis gr. An. fragilis (MDHC 102), right compound bone in medial (S) and lateral (T) views. U–V, Pseudopus apodus (MDHC 214), left compound bone in medial (U) and lateral (V) views. Abbreviations: ac, articular condyle with the quadrate; af, adductor fossa; ap, angular process; ar, articular; asa, articulation surface with the angular; asd, articulation surface with the dentary; asf, anterior surangular foramen; fct, foramen for the chorda tympani; lc, lateral crest; pra, prearticular; psf, posterior surangular foramen; rap, retroarticular process; sa, surangular; t, tubercle; tr, tympanic ridge. Scale bars = 1 mm.

Figure 51. Compound bones (continued). A, Laudakia stellio (MDHC 245), left compound bone in dorsal view. B, Lacerta agilis (MDHC 176), left compound bone in dorsal view. C, Chalcides ocellatus (MDHC 250), right compound bone in dorsal view. D, Anguis gr. An. fragilis (MDHC 102), right compound bone in dorsal view. E, Pseudopus apodus (MDHC 214), left compound bone in dorsal view. Abbreviations: ap, angular process; asf, anterior surangular foramen; psf, posterior surangular foramen; t, tubercle; tr, tympanic ridge. Scale bars = 1 mm.

Figure 52. Posterior end of the left compound bone of Lacerta viridis NHMW 663 in medial view, showing the strong expansion of the ventral margin. Scale bar = 1 mm.