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 : 565-566

Boidae B

Boidae B – Ivanov 1997a: 41, fig. 21.

MATERIAL EXAMINED. — 2 trunk vertebrae ( FSL 368343, FSL 368344).

DESCRIPTION

Trunk vertebrae ( Fig. 4 )

In lateral view, the basis of the neural spine is shifted anteriorly. Although the neural spine is incompletely preserved, it may be assumed that its cranial margin is vertical or slightly inclined posteriorly like the caudal margin. The neural arch is turned up caudally, the interzygapophyseal ridges are distinct and sharp. The lateral foramina are large and distinct, situated in shallow depressions. The subcentral ridges are indistinct and short. The synapophyses are very damaged. In dorsal view, the zygosphenal lip is clearly concave. The obovate (?subtriangular) prezygapophyseal articular surfaces are damaged, the prezygapophyseal processes are very short,

C

however, they are well-perceptible from the dorsal view. Epizygapophyseal spines are lacking. In ventral view, both the subcentral ridges and wide subcentral grooves are relatively indistinct, the subcentral foramina are large and situated close to the distinct haemal keel. The haemal keel may be wide or relatively narrow. The postzygapophyseal articular surfaces are approximately oval. In cranial view, the neural arch is slightly vaulted, the neural canal is subcircular with distinct lateral sinuses. The massive zygosphenal lip is straight to slightly concave. The prezygapophyses are strongly tilted upward. Wide depressions are situated on either side of the rounded cotyle, the paracotylar foramina are lacking. Metrical measurements: larger vertebra: cl = 3.72; naw = 4.51; cl/naw = 0.82; smaller vertebra: cl = 3.52; naw = 3.99; cl/naw = 0.88.

DISCUSSION

Both the low ratio cl/naw (lower than 1.00) and the massive structure of vertebrae point to the affiliation to the family Boidae . The morphotype Boidae B does most probably not belong to the subfamily Erycinae because the neural arch is not clearly flattened dorso-ventrally, which is a char- acteristic of erycine snakes. The vertebrae of the morphotype Boidae B belong most likely to a small representative of the Boinae or Pythoninae . The Boidae B differs from Python sp. in: 1) the less vaulted neural arch; 2) the prezygapophyses which are tilted upward. Based on the limited material, a more precise determination was not possible.

Figures

FIG. 4. — Boidae B from the lower/middle (MN 4/5) Miocene of Vieux Collonges, mid-trunk vertebra (FSL 368343); A, lateral view; B, dorsal view; C, ventral view; D, cranial view; E, caudal view. Scale bar: 2 mm.