Squamata indet.

Vasilyan, Davit, Cernansky, Andrej, Szyndlar, Zbigniew & Moers, Thomas, 2022, Amphibian and reptilian fauna from the early Miocene of Echzell, Germany, Fossil Record 25 (1), pp. 99-145 : 99

Squamata indet.

Fig. 17A-F

Material.

One premaxilla HLMD-Ez 1989, right quadrate HLMD-Ez 2002, left pterygoid HLMD-Ez 2003, two osteoderms HLMD-Ez 2000-2001.

Description.

Premaxilla: Premaxilla HLMD-Ez 1989 (Fig. 17A-C ) represents a small element, although with a more-or-less robust appearance. It is almost fully preserved. It is a single, unpaired T-shaped element (note, a groove or break is running through the midline, see remarks). The premaxilla bears seven-tooth positions with three teeth still attached to the dental parapet. The laterally extended maxillary processes are well developed. They are rather short than long. They possess an articulation facet for the maxilla on their dorsolateral surfaces. The fragmentarily preserved nasal process is wide, its external surface is flat. Here, a few small vestiges of osteoderms attached to the bone are present. In anterior and posterior views, the base of the nasal process is laterally constricted. Thus, the lateral margins in the lowest region of the process are rounded, having a cut-out like appearance. Dorsally, this region is wide, having more-or-less parallel lateral margins. The most dorsal preserved portion of the process narrows abruptly again, but the rest of the process - the posterodorsal portion with a termination - is broken off. On the internal side, there is a sagittal ridge running along the entire length of the preserved nasal process. It separates the facet for the nasals on both sides. On the lateral side, the ethmoidal foramen is located close to the base of the nasal process. The supradental shelf is formed by two segments, which are well expanded posteriorly. The dorsal side bears the vomerine process, which forms a small bulge. The short, weakly bilobed median incisive process is located ventral to the supradental shelf.

Remarks.

Although the right and left premaxillae are fused, note that there is a fracture-like structure (or a tiny groove) running through the central portion of the element. However, it is unclear whether this is postmortal damage only or reflects the fusion of the right and left premaxillae during ontogeny. Even if it is only a fracture caused by damage, the central region might be weaker due to the late fusion and, thus, prone to breakage when pressure is applied. Among Chalcides species, a groove indicating a fusion is often present in various degrees (for Ch. ocellatus , see Digimorph.org 2002-2012; in some, e.g., Ch. polylepis , the right and left premaxillae are separated; see, e.g., Caputo (2004); pers. obs. of A. Č.). However, its lacertid affinity can not be excluded. The premaxilla of lacertids is formed by a single element (see, e.g., Čerňanský and Syromyatnikova 2019). If the specimen HLMD-Ez 1989 represents a lacertid, the present groove is caused by postmortal damage only. In any case, we decided to allocate this specimen to Squamata indet.

Quadrate: A right quadrate is available in the material (Fig. 17D, E ). It is a slender, dorsoventrally elongated element. In lateral view, the quadrate is anteroposteriorly narrow, with an anteriorly expanded, rounded anterior margin. Here, the sharp and laterally expanded tympanic crest is present. This crest is continuous from the cephalic to the mandibular condyle. The crest is slightly angled approximately in the mid-region. Further dorsally, it fluently and gradually continues without being distinctly separated by a sharp angle from the portion formed by the cephalic condyle. The dorsal portion of the cephalic condyle protrudes slightly posteriorly. The ventral half of the quadrate narrows gradually ventrally. The ventral region ends with the saddle-shaped mandibular condyle. It is slightly smaller than the cephalic condyle. The medial surface possesses a distinct medial crest. Posterior to this crest, the bone is pierced by a quadrate foramen located in the ventral one-third of the dorsoventral height of the element.

Remarks.

The morphology of the quadrate HLMD-Ez 2002 is similar to that of lacertids (see e.g., Čerňanský and Syromyatnikova 2019) rather than anguids. Note, however, that the general shape of the lacertid quadrate resembles that of scincids (see Villa and Delfino 2019b),

Pterygoid: The left pterygoid is incompletely preserved (Fig. 17F, G ). It is a tri-radiate, Y-shaped element. Its ventral portion bears a distinct dentition located in the central region. Only the base of the ectopterygoid process is preserved, being broad. From its posterior region, a sharp crest runs to the quadrate process. Here, the crests border a fossa located laterally on the process. The quadrate process is long but note that its end is broken off. The fossa columellae (= epipterygoid fossa), which is present on the dorsal side, is large and elliptical.

Identification of isolated elements as pterygoids is problematic and caution is needed. However, the morphology of HLMD-Ez 2003, e.g., the absence of the obtuse process (ventromedial process sensu Conrad 2008), indicates that we can exclude Anguidae here. Its morphology, including the crests bordering a fossa located laterally on the quadrate process, resembles skinks. Although note that dentition is absent in e.g., Chalcides occelatus , but present in, e.g., Plestiodon fasciatus (see Caputo 2004; Digimorph.org 2002-2012).

Osteoderm: Two osteoderms are available in the material. The larger osteoderm HLMD-Ez 2000 (Fig. 17H-J ) is roughly trapezoidal in shape. It is thick, with distinct external bulging. Its external surface expands in the anterior direction, being gradually more pronounced. This gives a convex appearance in cross-section. The whole osteoderm gradually narrows anteriorly. Here, the well-developed anterior overlap surface is located, forming one-third of the entire anteroposterior length of the osteoderm. Its anterior mid-region bears a short groove, which is present on the internal side as well. The region posterior to the overlap surface bears ornamentation. The ornamentation appears to be rather weak and not dense, being formed mostly by ridges and pits, connected by short grooves in some cases. The medial ridge is absent. The internal aspect of the osteoderm is not flat, but is rough. It has several irregularly distributed pits, foramina, and a few grooves near the posterior end.

The smaller specimen HLMD-Ez 2001 (Fig. 17K-M ) is wide. Its width is slightly greater than its anteroposterior length. The anterior portion, which bears a narrow overlap surface, is triangular, whereas the posterior portion has a round margin. The osteoderm is thick, although note that it is narrower relative to its size if compared to the larger one. Here, the internal surface of the smaller osteoderms is slightly concave. The ornamentation of the external surface is formed by densely spaced ridges and grooves running from the ossification centre; those ones located on the periphery are prolonged.

The differences in these two osteoderms can be caused by ontogeny and different origins regarding the body topology. Overall, this type of osteoderms resembles the osteoderms described by Čerňanský (2016; fig. 11) as Squamata indet. 2 from the lower Miocene of the Austrian locality Oberdorf. They might very likely belong to skink.

Figures

Figure 17. Squamata indet. from the Echzell locality. Premaxilla HLMD-Ez 1989 in (A) anterior, (B) posterior, and (C) lateral views. Right quadrate HLMD-Ez 2002 in (D) lateral, and (E) medial views. Left pterygoid HLMD-Ez 2003 in (F) dorsal and (G) ventral views. Osteoderms HLMD-Ez 2000 (H-J) and 2001 (K-M) in (H, K) external, (I, L) internal and (J, M) posterior views.