Palaeovaranidae Georgalis, 2017

Čerňanský, Andrej, Smith, Richard, Smith, Thierry & Folie, Annelise, 2024, Timing of intercontinental faunal migrations: Anguimorph lizards from the earliest Eocene (MP 7) of Dormaal, Belgium, Zoological Journal of the Linnean Society 201 (4), pp. 1-25 : 16-18

Palaeovaranidae Georgalis, 2017

Palaeovaranidae indet.

( Fig. 10 )

1962 Necrosaurus —Hecht and Hoffstetter: 11.

1990 Necrosaurus sp. —Augé: 166–167.

2003 cf. Necrosaurus –Augé: 443, fig. 1I.

2005 Necrosaurus sp. —Augé: 287.

Referred material: IRSNB R 499, right maxilla, IRSNB R 500, osteoderm.

Locality and horizon: Dormaal, Flemish Brabant, eastern Belgium, Dormaal Member, Tienen Formation, Landen Group, earliest Eocene (MP 7).

Description

Maxilla: Only a fragment of the right maxilla is preserved (IRSNB R 499; Fig. 10A–E ). It possesses nine tooth positions (three and half teeth are still preserved). The bone is lightly built and rather thin. In lateral view, between the dorsal and ventral margins, the wall of the maxilla is distinctly concave. The facial process is only partly dorsally preserved, being lateromedially thin. The external surface of the bone is smooth. It is pierced by a series of large labial foramina (six are present in the preserved portion) located in a row on the ventral section of the bone surface. Posterior to the last labial foramen, several teeth are present (at least three are preserved). Besides labial foramina, several small foramina are present, being located more dorsally ( Fig. 10A ). In medial view, there is a thin supradental shelf that slightly widens posteriorly. It is not markedly medially expanded. Laterally, in the dorsal portion of the shelf (between the shelf and the facial process), there is a narrow longitudinal depression—the sulcus for the nasolacrimal duct. The maxilla immediately laterally to the supradental shelf is burrowed by the superior alveolar canal. Its posterior opening, the superior alveolar foramen, is located in the posterior section, being large and anteroposteriorly elongated. It is located at the level of the sixth preserved tooth position (counted from anterior). The foramen is dorsolaterally bordered by a lip of bone.

Dentition: The dentition is subpleurodont (sensu Hoffstetter 1954, 1955),thejawparapetislowandthebasesoftheteethareattachedto a sloping, concave surface, without any angle between two different planes ( Fig. 10A–E ). The tooth bases are mesiodistally broad and bear well-preserved typical basal striae, i.e. plicidentine. These basal infoldings are widely spaced. The tooth tips are pointed, tall, and strongly curved distally and slightly lingually. The mesial and distal cutting edges are well developed. Although the mesial one is more distinct in the anterior preserved tooth, both mesial and distal cutting edges are more-or-less equal in the posterior teeth.

Osteoderm: The osteoderm IRSNB R 500 ( Fig. 10F–K ) is oval in shape with an external medial high keel running through the entire length of the osteoderm. It is sculptured by pits and ridges. The internal surface is slightly concave with small foramina [neurovascular foramina sensu Smith and Gauthier (2013)].

Remarks

The overall morphology and plicidentine support allocation of the maxilla to a varanoid ( Kearney and Rieppel 2006, Georgalis and Scheyer 2019). Although preserved diagnostic features are limited, the maxilla can be distinguished from Varanus and Saniwa ensidens in having at least three tooth positions posterior to the last supralabial foramen. In Saniwa orsmaelensis , which was previously known from Dormaal (there is only one species of Saniwa in Dormaal for the moment; see: Augé et al. 2022), four teeth are present posterior to the last supralabial foramen. It should be noted, however, that several tooth positions posterior to the last labial foramen are also present in Paranecrosaurus feisti ( Stritzke, 1983) , which is known only from the Early–Middle Eocene of Messel in Germany ( Smith and Habersetzer 2021; previously this taxon was regarded as Saniwa feisti , see: Stritzke 1983). The diagnostic parts of palaeovaranid maxillae, however, are mainly found in medial view. The presence of a distinctly developed nasal crest on the dorsomedial surface of the nasal process is a distinguishing feature of Palaeovaranus (previously mentioned in the literature with the name Necrosaurus ; see: Georgalis 2017) and Paranecrosaurus [nasolacrimal ridge sensu Smith and Habersetzer (2021)]. Unfortunately, this portion in the Dormaal maxilla is heavily damaged and there is no indication of its presence. However, this jaw fragment is characterized by an alternate tooth replacement (teeth are widely spaced), which is diagnostic for Palaeovaranus ( Augé and Smith 2009) . Moreover, it seems that the prominence of the plicidentine is not as prominent as in Saniwa ; it is represented by plicidentine with widely spaced striations, which is more typical for Palaeovaranus ( Georgalis and Scheyer 2019, Georgalis et al. 2021). The mesial and distal cutting edges on tooth tips are present, but this feature can also be find in Palaeovaranus [ Necrosaurus in Augé and Smith (2009: fig. 7)], Paranecrosaurus ( Smith and Habersetzer 2021) , and Saniwa ( Rieppel and Grande 2007) . Finally, if we compare the specimen IRSNB R 499 ( Fig. 10B ) with the specimen attributed to ‘ Necrosaurus ’ sp. from the Oligocene of Boutersem, also in Belgium (see: Augé and Smith 2009: fig. 7), we can observe several similarities, such as the general shape of the teeth, space between the infoldings, curvature of the tooth crowns, and presence of mesial and distal cutting edges on the tooth crowns.

Figures

Figure 10. Palaeovaranidae indet. from the earliest Eocene of Dormaal.Right maxilla IRSNB R 499 in A, lateral; B, medial with detail of teeth; C, dorsomedial; D, dorsal; and E, ventral views. Osteoderm IRSNB R 500 in F, external; G, internal; H, right side of the osteoderm; I, left side of the osteoderm; J, anterior; and K, posterior views (all micro-CT visualizations).