Lacertidae Oppel 1811
Makaleler > Tam Makale · 2021
Yazarlar: Georgalis, Georgios L., Čerňanský, Andrej, Serdar MAYDA
, Uluslararası, 2021
Özet
Lacertidae indet. (morphotype 1) (Figs 6; 7) MATERIAL. — Turkey. Kavakdere: a right maxilla (EUNMH PV 14052). Kocayarma: three maxillae (EUNMH PV 14061, EUNMH PV 14064, and EUNMH PV 14066) and a dentary (EUNMH PV 14063). DESCRIPTION Maxilla The description is based on several specimens. Specimen EUNMH PV 14052 represents a fragment of a right maxilla (Fig. 6). It is robustly built. The labial surface of this portion is pierced by two supralabial foramina. The nasal process is broken off, only its base is present. The lingual side bears a broad and massive supradental shelf, which is slightly convex dorsally. Five tooth positions are preserved, where four teeth are still attached (Fig. 6C). The superior alveolar foramen is located at the level of the last posterior preserved tooth. The further posterior portion is damaged and missing in EUNMH PV 14052. This portion is, however, present in the Kocayarma specimen EUNMH PV 14064. In this specimen, the posteroventral process of the maxilla is not stepped, but gradually rises dorsally in anterior direction (Fig. 7 D-E). In labial view, a weak ornamentation is present in the dorsalmost region. This section possesses no foramina. The same specimen bears six tooth positions, where all teeth are still attached. The supradental shelf is partly damaged. The posterior lingual region bears an articulation facet for the jugal on its dorsal side. Dentary An anterior portion of the right dentary is preserved (EUNMH PV 14063). It is a ventrally arched bone, with a slight medial curvature at its anterior end (Fig. 7 G-I). The otherwise smooth labial surface is pierced by a single series of five labial foramina. Meckel’s groove is fully open in lingual view, but rather narrow. It continues to the small rectangular symphysis anteriorly. The subdental shelf is moderately robust in this section and appears to be slightly rounded in cross-section.The dental crest is high, supporting medially 13 tooth positions (four teeth are still attached). The further posterior portion is, however, broken off and missing. Dentition Tooth implantation is pleurodont. The teeth are large, robust and closely spaced. They have bicuspid tooth crowns. There is a triangular dominant cusp and a smaller mesial one (note that in EUNMH PV 14052, the posteriormost preserved tooth has a small inconspicuous distal bulge that can be interpreted as incipient additional cusp). The lingual side of the crowns is slightly flattened. The strong distinct striation here is present mainly in EUNMH PV 14052 (Fig. 6C). It possesses around 11 diverged distinct striae which incline mesially and distally in ventral direction. The labial surface is smooth. The tooth necks are slightly enlarged lingually. The tooth bases are covered by sediment, but some of them exhibit large circular resorption pits. COMMENTS This lacertid morphotype is characterized by massively built maxillae. The strongly developed striation of the lingual side of the tooth crowns, as present in the Kavakdere specimen EUNMH PV 14052, is not so distinct in other specimens from the nearby slightly younger locality of Kocayarma (although striation is obviously present in the latter material as well). We interpret this difference to be due to preservation reasons and/or possibly individual and ontogenetic variation or even chronostratigraphic variation (considering that the specimens from the two localities are not absolutely contemporary [allotemporal sensu Smith & Gauthier 2013]). The tooth morphology resembles that in the extant members of the genus Timon Tschudi, 1836, in the following aspects (see Kosma 2004; Čerňanský & Syromyatnikova 2019): 1) teeth are robust; 2) tooth crowns medially flattened; 3) the presence of a distinct striations on the lingual side (the maximum twelve striae is mentioned for Timon pater [Lataste, 1880] by Kosma (2004); 4) striae converge apically; 5) bicuspid teeth have been reported for T. pater by Kosma (2004), where in some specimens, a tendency to tricuspidity can be observed; and 6) large circular resorption pits at the tooth bases. Moreover, the posteroventral process of maxilla is not stepped, which is also a character present in Timon (see Čerňanský & Syromyatnikova 2019). However, caution is needed here, as the interpretation of such small jaw fragments is always tricky. The similarities in dentition can also be interpreted by convergence due to similar diet preferences. Indeed, robust bicuspid teeth together with the not stepped posteroventral process of maxilla, is also present in the European Paleogene taxon Plesiolacerta Hoffstetter, 1942 (Čerňanský & Augé 2013; Čerňanský et al. 2016). This extinct taxon also shares many other characters with the extant Timon (see Čerňanský & Syromyatnikova 2019). The dentary of Plesiolacerta is characterized by the subdental shelf being rounded in cross-section. This feature is difficult to evaluate in EUNMH PV 14063, because only its anterior portion is preserved. In any case, it appears to be rounded as well. The anterior dentary region in both Plesiolacerta and Timon is strongly arched, but this appears to be not so pronounced in EUNMH PV 14063. More complete material is therefore needed to resolve the taxonomy of this Oligocene Turkish lacertid. As such, for now, we decided to allocate this maxilla as Lacertidae indet. (morphotype 1), although some similarities to Plesiolacerta and Timon are obvious.