Lacertidae

Lacertidae View in CoL View at ENA ( Figs 2G–Q View Figure 2 , 3H View Figure 3 )

Frontals of lacertids are paired, but they can fuse during ontogeny. Only in Ac. erythrurus , E. arguta (Pallas, 1773) and Ophisops elegans do they fuse early in the postnatal ontogeny and compose, therefore, an unpaired bone for most of the life of the animal ( Fig. 2G, H View Figure 2 ); in this case, the suture line is not visible on the ventral surface. The medial constriction, which is always well-evident in juveniles ( Fig. 4 View Figure 4 ), varies among different species in the adults: frontals of Ac. erythrurus , Eremias arguta and Ophisops elegans are strongly constricted ( Fig. 2G, H View Figure 2 ), those of Archaeolacerta bedriagae (Camerano, 1885) , Algyroides , Dalmatolacerta oxycephala , Dinarolacerta mosorensis , Hellenolacerta graeca (Bedriaga, 1886) , Iberolacerta bonnali , I. cyreni , I. horvathi , I. monticola , Podarcis bocagei , Po. carbonelli , Po. filfolensis (Bedriaga, 1876) , Po. hispanicus , Po. lilfordi (G ünther, 1874), Po. melisellensis (Braun, 1877) , Po. milensis (Bedriaga, 1882) , Po. muralis , Po. pityusensis (Boscá, 1883) , Po. siculus (Rafinesque-Schmaltz, 1810) , Po. tauricus (Pallas, 1814) , Po. tiliguerta , Po. waglerianus Gistel, 1868 , Psammodromus , Ti. lepidus and Zootoca vivipara (Lichtenstein, 1823) are slightly constricted ( Fig. 2K–Q View Figure 2 ) and those of Lacerta have roughly parallel margins ( Fig. 2I, J View Figure 2 ). As a rule, the posterior end is twice as large as the anterior end, giving a shape that roughly resembles an L to the unfused bone and a T to the fused one. However, in adults of Hellenolacerta graeca , Lacerta bilineata , Lacerta trilineata , Lacerta viridis and Ti. lepidus the difference in width between the anterior and posterior ends is lower ( Fig. 2I, J, M, N View Figure 2 ). Both medial and lateral processes are present and moderately developed, even if the medial one may be less distinguishable in some specimens. Even though in juveniles and in adults of most species they could also appear as single processes ( Fig. 4 View Figure 4 ; see also Barahona, 1996), lateral processes are usually bifurcated (always so in Psammodromus ): their medial branch is usually longer than the medial process, whereas the lateral one is slightly shorter than the latter. Low ridges are present on the dorsal surface of the two branches, separating the articulation surface with the nasal from that with the maxilla (ridge on the medial branch) and the latter from the one with the prefrontal (ridge on the lateral branch). All the articulation surfaces, those with the postfrontal included, are large and well distinct, although the ones with the facial process of the maxilla are reduced or even absent in some species ( Algyroides marchi Valverde, 1958 , Al. moreoticus Bibron & Bory, 1833 , Iberolacerta bonnali , I. cyreni , I. horvathi , I. monticola , Lacerta , Ti. lepidus and Z. vivipara ; Fig. 2I, M, P View Figure 2 ). Articulation surfaces with the prefrontal and the postfrontal are distinctly far from each other ( Fig. 3H View Figure 3 ). Posterolateral processes are well developed and can be roughly pointed or more rounded. The posterior margin is strongly irregular and can be wavy (in Ac. erythrurus and Ophisops elegans , whose margin has a moderately large posterior expansion in the middle; Fig. 2G, H View Figure 2 ). Except for Ac. erythrurus and Ophisops elegans , this margin also has little ( Al. marchi , Al. moreoticus , I. bonnali , I. horvathi , Po. filfolensis , Po. lilfordi and Z. vivipara ; Fig. 2P, Q View Figure 2 ) or strongly (other species; Fig. 2I–N View Figure 2 ) developed interdigitations, which are less marked in very young individuals ( Fig. 4 View Figure 4 ). Cristae cranii are moderately low in their posterior portion, whereas the anterior one is more developed and forms a long and thin anterior process with an irregular ventral margin. Arnold et al. (2007) stated that the anterior process is often absent in Z. vivipara . The ventral surface is smooth, with only two very shallow symmetrical sunken areas in its anterior-half and on its posterior end. A subtriangular articulation surface housing the parietal tabs of the parietal is also visible by the posterolateral corner of the bone. A dermal ornamentation is present dorsally, which usually becomes more marked with increasing size and age, being well developed in large animals but significantly less distinguishable in small ones. Roughly at the beginning of the posterior third of the bone, the sulcus separating frontal and frontoparietal shields is visible ( Fig. 2G, K View Figure 2 ). In some specimens of Ti. lepidus , this sulcus is located at midlength ( Fig. 2O View Figure 2 ; see also Čerňanský, 2010), whereas in adults of Lacerta and in other individuals of Ti. lepidus it is usually placed at three-fifths of the length of the frontal from the anterior end ( Fig. 2I View Figure 2 ). The ornamentation is poorly developed (sometimes almost absent, particularly in Ophisops elegans ) in Ac. erythrurus , E. arguta and Ophisops elegans , being visible mostly on the posterior-half of the bone ( Fig. 2G View Figure 2 ). This condition approaches the one seen in juveniles of other, small-sized species. Measurements of the frontal of lacertid species are given in the Supporting Information 3.