Pseudeumeces sp.

Georgalis, Georgios L., Čerňanský, Andrej & Klembara, Jozef, 2021, Osteological atlas of new lizards from the Phosphorites du Quercy (France), based on historical, forgotten, fossil material, Geodiversitas 43 (9), pp. 219-293 : 236-240

Pseudeumeces sp.

( Figs 15-17 )

REFERRED SPECIMENS. — A left maxilla (NHMW 2019/0051/0004); a left dentary (NHMW 2019/0051/0003); a right dentary (NHMW 2019/0051/0005).

DESCRIPTION

Maxilla NHMW 2019/0051/0004 ( Fig. 15 )

Only one such element is available in our collection, the left maxilla NHMW 2019/0051/0004 ( Fig. 15 ). This specimen is almost completely preserved. In medial view, the supradental shelf is well medially expanded, having rounded (dorsally convex) course ( Fig. 15B ). The maxilla bears 11 tooth positions (10 teeth are still attached). However, the premaxillary process is broken off and only its posterior root portion is preserved. Thus, it can be estimated that the tooth number in a complete tooth row was around 12. The superior alveolar foramen is located at the level between the 3rd and 4th tooth positions (counted from posterior). Posterior to this, the maxilla protrudes into the posteroventral process, having a facet for jugal on its dorsal internal side. A facet for the palatine is positioned medial to the superior alveolar foramen. The posteroventral process of the maxilla slightly narrows posteriorly, although its termination is not pointed, but rather stepped. This posteriormost portion does not bear dentition. In the anterior half of the bone, the nasal process is well dorsally elevated, being high. Its dorsal end slightly bents medially. However, the posterodorsal tip, which forms the contact with the fron- tal, is broken off. On the medial side of the nasal process, the carina maxillaris starts to rise dorsally at the level of the 3rd preserved tooth (counted from anterior). Further, it is inclined posteriorly and thus it does not reach a high level dorsally. In the dorsal portion of the process, a facet for the prefrontal is present.

In lateral view, the ventral region of the maxilla is pierced by six labial foramina of various sizes ( Fig. 15A ). The posteriormost one is located at the level of the 4th tooth position (counted from posterior). The dorsally located nasal process is completely covered by three osteoderms. These are clearly demarked by sulci. The sulci meet all together at the level of the 4th tooth position (counted from ante- rior), forming a Y-shaped structure. The anteroventral osteoderm is the smallest one, whereas the largest is the posterior osteoderm. All three osteoderms are sculptured. The sculpture consists of densely arranged pits and ridges running to the periphery. The posteroventral process, posterior to the level of osteoderm, has bulged dorsal margin. Dentaries NHMW 2019/0051/0003 and NHMW 2019/0051/0005 ( Figs 16 ; 17 )

Specimen NHMW 2019/0051/0005 is small in size and slightly damaged, whereas NHMW 2019/0051/0003 represents only fragment of the posterior portion of the dentary. NHMW 2019/0051/0005 possesses 15 tooth positions, with seven teeth being still attached ( Fig. 16 ). The dorsal crest is high and the teeth only slightly exceed it dorsally. Meckel`s groove is fully open, but the ventral portion of the dentary is broken off. In any case, the dentary is narrow rather than robust. Its lateral surface is pierced by five labial foramina. In the posterodorsal region of the dentary, the wedge shaped, well defined facet for the anterolateral process of coronoid is present. It reaches the level of the penultimate tooth position. NHMW 2019/0051/0003 possesses only six tooth positions, with five teeth preserved ( Fig. 17 ); its further anterior region is broken off and missing. The facet for the anteromedial process of the coronoid reaches the level of the last posterior tooth. On lateral side, the facet for the anterolateral process of coronoid is well defined, reaching the level between the last and penultimate tooth position.

Dentition

The dentition is pleurodont and amblyodont. The teeth are closely spaced. The tooth crowns bear delicate striations on both maxillary and dentary teeth. The maxillary tooth length varies, resulting in a sinuous occlusal surface. Here, the teeth in the posterior section are more robust except for the last two. The teeth in the anterior portion of the tooth row are slightly pointed and curved posterolingually. On some of those maxillary teeth, there is a very small indication of an indistinct, incipient mesial cusp.

REMARKS

The maxilla NHMW 2019/0051/0004 bears 12 tooth positions, whereas 15 are present in that of Pseudeumeces cadurcensis (see Augé 2005; Augé & Hervet 2009). For this reason, the maxilla NHMW 2019/0051/0004 potentially pertains to the above described species Pseudeumeces kyrillomethodicus n. sp. However, as there is a lack of a strong support for such association based on the available material, we decided to allocate this maxilla only as Pseudeumeces sp. Small differences in the anterior maxillary teeth of NHMW 2019/0051/0004 and the dentary teeth of Pseudeumeces kyrillomethodicus n. sp. can be explained by an ontogenetic change. Judging from the smaller size of the maxilla NHMW 2019/0051/0004 relative to dentaries, the former specimen most likely represents a late juvenile (or subadult) individual. Similar changes have been observed in both extant and extinct lacertids. For example, in the early Miocene Janosikia ulmensis ( Gerhardt, 1903) , vestiges of mesial cusps are present on some anterior maxillary teeth in a juvenile specimen (see Čerňanský et al. 2016b). Additionally, the ontogenetic change in the tooth morphology is sometimes observed in the extant Gallotia stehlini ( Schenkel, 1901) as well, where the juvenile tricuspid teeth are replaced by multicuspid ones in adult individuals ( Barahona et al. 2000).

The maxilla NHMW 2019/0051/0004 further differs from that of Dracaenosaurus in the following features: 1) maxillary tooth number is ~12 rather than 7; 2) the posteroventral process of the maxilla is not markedly high as it is in D. croizeti ; and 3) the presence of three well developed osteoderms attached to the nasal process of maxilla.

Two dentaries are also referred to Pseudeumeces sp. The specimen NHMW 2019/0051/0005 represents the smallest lacertid dentary in our sample. It is very likely that it represents a juvenile (or subadult) ontogenetic stage, that could potentially pertain to the above described Pseudeumeces kyrillomethodicus n. sp. Nevertheless, in comparison with that taxon, NHMW 2019/0051/0005 does not appear to be so robust and the facet for the anterolateral process of coronoid reaches at the level of the penultimate tooth position.In the other specimen, the fragment of left dentary (NHMW 2019/0051/0003), this facet reaches the level between the last and penultimate tooth. Moreover, only the last posterior tooth was reduced (it is absent, but its size can be estimated based on its tooth loci). These characters are in a sharp contrast with the type material of Pseudeumeces kyrillomethodicus n. sp. Therefore, we cannot exclude that this material does not pertain to Pseudeumeces cadurcensis , which also occurs in the Oligocene of the Phosphorites du Quercy and shares these features (e.g., Augé & Hervet 2009). The proper taxonomic allocation of fragmentary material needs always to be met with caution. This is especially true for similar forms such as those discussed herein.

Figures

FIG. 15. — Pseudeumeces sp. Photographs of left maxilla NHMW 2019/0051/0004 in lateral (A), medial (B), and dorsal (C) views. Scale bar: 2 mm.

FIG. 16. — Pseudeumeces sp. Photographs of right dentary NHMW 2019/0051/0005 in lateral (A), medial (B), and dorsal (C) views. Scale bar: 2 mm.

FIG. 17. — Pseudeumeces sp. Photographs of left dentary NHMW 2019/0051/0003 in lateral (A), medial (B), and dorsal (C) views. Scale bar: 2 mm.