Boidae, Gray, 1825

Ivanov, Martin, 2000, Snakes of the lower / middle Miocene transition at Vieux Collonges (Rhône, France), with comments on the colonisation of western Europe by colubroids, Geodiversitas 22 (4), pp. 559-588 : 566-567

Boidae C

Boidae C – Ivanov 1997a: 41-42, fig. 22.

MATERIAL EXAMINED. — 4 trunk vertebrae ( FSL 368345- FSL 368348).

DESCRIPTION

Trunk vertebrae ( Fig. 5 )

In lateral view, the cranial margin of the neural spine is located at the anterior third of the vertebral length. The cranial margin of the only preserved, but very damaged, neural spine is vertical, the caudal margin is broken off. The interzygapophyseal ridges are distinct and sharp. The large lateral foramina are not situated in depressions. The subcentral ridges are distinct and vaulted dorsally, extending from strongly damaged synapophyses to the base of the condyle. In dorsal view, the zygosphenal lip is characterised by distinct lateral lobes, the median lobe is wide and blunt. The prezygapophyseal articular surfaces are subtriangular, the prezygapophyseal processes are very short and invisible from the dorsal view. Epizygapophyseal spines are lacking. In ventral view, the subcentral ridges and grooves, as well as the deep haemal keel are distinct; the keel expands near the cotyle. The ventral margin of the haemal keel is rounded in the cranial part of vertebrae but, in the caudal part, it is relatively sharp. The subcentral foramina are distinct and large, they open close to the haemal keel. The postzygapophyseal articular surfaces are expanded laterally. In cranial view, the neural arch is arched, the neural canal is subcircular with small lateral sinuses, and the gracile zygosphenal lip is straight. The prezygapophyses are tilted upward. Deep depressions are situated on the both sides of the dorsoventrally flattened cotyle, paracotylar foramina are absent. The metrical measurements are as follows (n = 3): cl: or = 3.49-4.16; naw: or = 3.99-4.93; cl/naw: or = 0.84-0.87, mean 0.86 + 0.02.

DISCUSSION

The vertebrae belong undoubtedly to the family Boidae based on the massive structure and the low ratio cl/naw (lower than 1.00). A distinctly vaulted neural arch excludes the affiliation to the subfamily Erycinae . The absence of the paracotylar foramina is insufficient for distinction between subfamilies Boinae and Pythoninae (Szyndlar 1994) . The morphotype Boidae C differs from the Boidae B on the basis of the following features: 1) the basis of the neural spine is located on the anterior third of the vertebral length; 2) the zygosphenal lip is not so massively built; 3) the lateral sinuses of the neural canal are small. The Boidae C differs from Python sp. mainly in: 1) the less vaulted neural arch; 2) the much more gracile zygosphenal lip.

Figures

FIG. 5. — Boidae C from the lower/middle (MN 4/5) Miocene of Vieux Collonges, mid-trunk vertebra (FSL 368346); A, lateral view; B, dorsal view; C, ventral view; D, cranial view; E, caudal view. Scale bar: 2 mm.