Scincoidea Oppel, 1811 (sensu Zheng & Wiens, 2016), 1870

Cernansky, Andrej & Vasilyan, Davit, 2024, Roots of the European Cenozoic ecosystems: lizards from the Paleocene (~ MP 5) of Walbeck in Germany, Fossil Record 27 (1), pp. 159-186 : 159

Scincoidea Oppel, 1811 (sensu Zheng & Wiens, 2016)

Fig. 7

Parasauromalus paleocenicus ? Scincoidea indet.

Material.

One right maxilla MLU.GeoS.4057, one left maxilla MLU.GeoS.4058.

Description.

Maxilla. Two maxillae are preserved. The specimen MLU.GeoS.4057 is larger and represents a fragment of the right maxilla around the superior alveolar foramen (Fig. 7A, B ). The anterior and posterior portions are broken off. The specimen possesses nine-and-a-half tooth positions (eight teeth are still attached). The lateral surface is eroded, but it can be estimated that the preserved portion was smooth. It is pierced by three supralabial foramina. The nasal process of the maxilla forms an almost perpendicular wall, although note that it is only partly preserved. It expands almost to the posterior end of the preserved portion of the bone. This posterior margin appears not to be stepped but gradually decreases posteriorly. In medial view, the supradental shelf is almost straight, only slightly expanded medially - however, it is heavily damaged. The superior alveolar opening is at the level of the sixth tooth position (counted from posterior). However, the exact number of teeth is unknown in this specimen due to the missing portions. Posterior to the opening, the bony dorsolateral wall is damaged, and thus, the area ventral to it, is exposed.

The specimen MLU.GeoS.4058 is smaller and slightly in overall better condition than 4057. It represents the left maxilla (Fig. 7C-H ) around the region of the superior alveolar foramen, but here, the posterior region is preserved. The lateral surface is smooth. It is pierced by three supralabial foramina: the first anterior is located at the level of the seventh tooth position; the second is at the level of the sixth tooth position and the last posterior one lies at the level of the third tooth position (all counted from posterior). The first two are moderately large, whereas the posterior one is smaller. The dental crest is well-developed, reaching more-or-less the half the tooth height. Nine tooth positions are preserved (six teeth are still attached). The supradental shelf is only partly preserved, especially in the posterior section of the bone. The opening of the superior alveolar canal is located at the level of the sixth tooth position (counted from posterior). However, the anterodorsal margin of the bone, which demarcates the opening, appears to be partially damaged. Due to this, the original opening might be slightly more posteriorly located, approximately at the level between the fifth and sixth tooth positions. The further posterior region is well-excavated, forming a longitudinal depression. The nasal process is partly preserved. Only its ventral portion remained intact. Its posterior margin appears to be stepped, but this region is partly broken off. Thus, an actual outline is unknown. The posterior portion protrudes into a short and narrow posteroventral process. It is bluntly ended.

Dentition. The tooth implantation is pleurodont. The teeth are tall, although the posterior last ones are slightly smaller (the last and penultimate teeth in MLU.GeoS.4058). The teeth are robust; the robustness increases posteriorly. They are slightly inclined posteriorly, being closely spaced with small interdental gaps. The apices are more-or-less rounded and blunt rather than having a sharp and pointed appearance (although it should be noted that the sixth tooth in MLU.GeoS.4058 has a roughly triangular appearance). The tooth crowns in MLU.GeoS.4057 are eroded, and some preservational artefact makes crowns look more rounded (plausibly because of digestion). The tooth crowns in MLU.GeoS.4058 are fairly preserved. In this specimen, the lingual surface of the crown in these teeth is concave, being curved inwards, whereas the labial one is distinctly convex. The lingual aspect of the crown is bordered by the culmen lateris anterior and culmen lateris posterior. No apicobasal crown striation can be recognized. The tooth crowns possess labial and lingual cusps, being transversally bicuspid. Note that this morphology is less noticeable, possibly due to preservation (the enamel appears to be slightly eroded - as occurs, for example, when teeth pass through stomach acid). However, further structures on enamel, such as striae, would be also affected (see Smith et al. 2021). The labial cusps form a somewhat rounded labial edge. For this reason, the overall appearance of these teeth is blunt. These labial cusps are slightly bent inwards - lingually, which is well-visible mainly in the tooth at the sixth tooth position (counted from posterior). Most tooth crowns show some longitudinal asymmetry (the mesial portion is longer than the distal one). The lingual cusps are small and hardly recognizable. They appear to be framed by short, mesially and distally running cristae lingualis dominans anterior and posterior. The tooth bases are well-expanded medially relative to the rest of the tooth shafts. The bases are pierced by oval resorption pits. A few teeth have huge pits, reaching almost over the half of their length. This feature is probably related to an artefact of preservation.

Remarks.

The material resembles mostly scincid, where the lingual cusp is usually framed by the broadly mesially and distally running cristae lingualis anterior and posterior rather than more-or-less vertical striae dominans anterior and posterior (e.g., Kosma 2004) - the presence of the lingual, well-separated cusp is more common among the cordylids than the scincids ( Folie et al. 2005). Transversely bicuspid teeth can be present in some gekkotans, e.g., eublepharids ( Sumida and Murphy 1987). In contrast to the robust Walbeck specimens, gekkotans have lightly built skeletons, which reflects their rarity in the fossil record ( Evans 2003, 2008). Transversely bicuspid teeth can be also present in teiids (in members of this group; in contrast to the Walbeck material, the teeth have extensive cementum depositions at tooth bases, see Estes 1983) and polyglyphanodontids, but the lingual cusp is much better developed in these taxa than the small cusp of the Walbeck material and scincoideans (see Nydam 1999). In lacertids, the lingual cusp, if present, is only weakly developed. Moreover, crown lacertids usually have bi- and tricuspid tooth crowns ( Čerňanský and Syromyatnikova 2019).

We cannot be certain whether both Walbeck specimens belong to the same taxon (because true crown morphology is only known for the well-preserved one - MLU.GeoS.4058). In fact, some features do not support an allocation to a single taxon (the supralabial foramina appear to be much larger in the poorly preserved specimen MLU.GeoS.4057, teeth look a little bit more robust). However, these differences can be related to the level of preservation, ontogenetic and/or individual variability. In any case, we provisionally allocated both specimens together as? Scincoidea indet.

Figures

Figure 7.? Scincoidea indet. from the Paleocene Walbeck locality. Right maxilla MLU. GeoS. 4057 (A, B) and left maxilla MLU. GeoS. 4058 (C - H) in lateral (A, C), medial (B, D), dorsal (E) and ventral (F) views. Detail of teeth of MLU. GeoS. 4058 in medial (G) and ventromedial (H) views.