Anguimorpha

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 : 18-19

Anguimorpha indet.

( Fig. 11A–F )

Referred material: IRSNB R 501, one dorsal vertebra.

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

Description

Dorsal vertebra: The single indeterminate anguimorphan dorsal vertebra in the sample ( Fig. 11A–F ) is large—the maximum anteroposterior length of the centrum is 9.4 mm, whereas its maximum width is 9 mm. The neural spine is low and robust. It starts to rise gradually, dorsally from slightly behind the anterior margin of the neural arch. This anterior portion of the spine is dorsally inclined in an angle of 37° from the horizontal. However, the dorsal margin of the neural spine is damaged. The neural canal is large and oval ( Fig. 11E, F ). The pre- and postzygapophyses are large, being oriented anterolaterally and posterolaterally in dorsal and ventral views ( Fig. 11A, B ). In dorsal view, the prezygapophyses markedly overreach the anterior margin of the neural arch, which is located almost at the level of the posterior border of the prezygapophyseal articular surfaces. Due to the presence of this wide notch (pars tectiformis of the neural arch between prezygapophyses), the dorsal surface of the centrum, posterior to the cotyle, is exposed in this view. The mid-region of the neural arch is slightly expanded anteriorly, having a small medial notch. Posterolaterally from this region, a shallow but wide depression is present on the dorsolateral wall on both sides of the neural arch. These depressions form slopes running from the anterolateral side of the neural spine to the posterior end of the prezygapophyseal articular surfaces. In contrast, the other area of the neural arch has a slightly swollen appearance. In posterior view, the neural arch is moderately vaulted and its roof-like posterior portion rises dorsally to the posterior base of the neural spine and gradually connects it with the postzygapophyses ( Fig. 11F ). Synapophyses are present, being laterally expanded. Their ends, however, are more-or-less damaged. Both cotyle and condyle are strongly dorsoventrally depressed. In lateral view, the cotyle is slightly inclined—its ventral rim is located more posteriorly than the dorsal one. Thus, the small dorsal portion of the cotyle is clearly visible in ventral view. In the condyle, the articular surface is developed mainly on the dorsal side rather than on the ventral side. Thus, the condyle is only slightly exposed in ventral view. In ventral view, the centrum is anteriorly widened, being almost triangular ( Fig. 11B ). The subcentral ridges are more-or-less straight, except at the condyle level, where a weak precondylar constriction is present (the width of the condyle is slightly larger than the width of the centrum immediately anterior to it). The small subcentral foramina are located in the anterior region of the centrum.

Remarks

Although the precondylar constriction might indicate the allocation of this dorsal vertebra IRSNB R 501, to Saniwa , the constriction is much more visible and forms a slightly more pronounced hook in Saniwa orsmaelensis from Dormaal (see: Augé et al. 2022: fig. 5C, F, I). However, the intracolumnar variation of Saniwa is unknown. The vertebra IRSNB R 501 is a posterior presacral and in some varanids, these are also wide but not to the extent as seen in Saniwa , as we can see in IRSNB R 501. A pseudozygosphene and pseudozygantrum are absent and the postzygapophyses are laterally expanded, which would indicate an attribution to Glyptosauridae (plausibly to ‘melanosaurines’ rather than glyptosaurines; see: Georgalis et al. 2021).

Squamata indet.

( Fig. 11G–L )

Referred material: IRSNB R 502, one caudal vertebra.

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

Description

Caudal vertebra: Only one caudal vertebra, IRSNB R 502, is preserved ( Fig. 11G–L ). It is large, with the maximum anteroposterior length of the centrum being 14.1 mm (taking into account its damaged condyle, the real length was slightly larger). The vertebra is extremely elongated and rather slender. The neural spine is reduced to a tiny crest on the neural arch and diminishes posteriorly. Anterior to this, approximately in the mid-portion of the vertebra, a large apophysis is located on the dorsal side of the neural arch ( Fig. 11G ). In lateral view, it seems to form a triangular structure, but its dorsal portion is, however, broken off ( Fig. 11I, J ). Both prezygapophyses are broken off. In anterior and posterior views, the neural canal is small ( Fig. 11K, L ). Only the right postzygapophysis is preserved. Its articular surface faces lateroventrally, with the pronounced dorsal inclination. The long centrum is laterally compressed, bearing a fossa on each side. Thus, the ventral portion has an hour-glass shape in ventral view ( Fig. 11H ). The condyle is damaged, whereas a rounded cotyle is partly preserved.

Remarks

Isolated caudal vertebrae are usually difficult to confidently identify. The vertebra has no sign of a fracture plane, which helps in assigning it to a varanoid lizard. The tail of Saniwa ensidens is markedly long (68% of the total length of the specimen; see: Rieppel and Grande 2007). Extremely elongated and rather slender caudal vertebrae are present in the distal section of the tail. However, at present no vertebra so distal has been described yet for Saniwa orsmaelensis . The origin of this vertebra from the caudal region is supported by the reduction of the neural spine and dorsal inclination of postzygapophyses ( Rieppel and Grande 2007). Its large size indicates that it belonged to a large lizard. Thus, Saniwa might be a good candidate. However, caution is needed, and we have decided to allocate this vertebra only as non-ophidian squamate.

Figures

Figure 11. Anguimorpha indet.1 (A–F) and Squamata indet. (G–L) from the earliest Eocene of Dormaal. Dorsal vertebra IRSNB R 501 in: A, dorsal; B, ventral; C, lateral right; D, lateral left; E, anterior; and F, posterior views. Caudal vertebra IRSNB R 502 in G, dorsal; H, ventral; I, lateral right; J, lateral left; K, anterior; and L, posterior views (all micro-CT visualizations) (all micro-CT visualizations).