Texasophis, Holman, 1977

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 : 567-568

Texasophis sp.

Colubrinae C – Ivanov 1997a: 96-97, fig. 43.

MATERIAL EXAMINED. — 7 trunk vertebrae ( FSL 368349- FSL 368355).

DESCRIPTION

Trunk vertebrae ( Fig. 6 )

In lateral view, the neural spine is broken off at the base. The interzygapophyseal ridges are welldeveloped, the lateral foramina are small, situat- ed closely below the interzygapophyseal ridges. Both the para- and diapophyses are small, indistinctly separated; the parapophyses are smaller than the diapophyses. The subcentral ridges are well-perceptible, they are long and straight. The neck of the condyle is relatively long. In dorsal view, the zygosphenal lip possesses an unusually projecting median lobe, the lateral lobes are smaller. The prezygapophyseal articular surfaces are oval, the prezygapophyseal processes are very short (about one-fifth of the length of the prezygapophyseal surfaces) and blunt. Epizygapophyseal ridges are missing. In ventral view, the shallow subcentral grooves are visible. Very small subcentral foramina are situated near the limit of the shallow haemal keel. The haemal keel expands close to the cotyle; on the ventral side small and indistinct subcotylar tubercles may be observed. The postzygapophyseal articular surfaces are irregularly shaped. In cranial view, the neural arch is clearly vaulted, the neural canal is large with small lateral sinuses. The zygosphenal lip is slightly convex; the paracotylar foramina are minute and situated in shallow depressions on either side of the rounded cotyle. In caudal view, the zygantral area is gracile, parazygantral foramina may occur. The metrical measurements are as follows (n = 4): cl: or = 3.25-3.97; naw: or = 2.14-.2.32; cl/naw: or = 1.52-1.71, mean 1.62 + 0.08.

A B

C

DISCUSSION

The fossil material is closely related to the extinct genus Texasophis because of the following features: 1) the vaulted neural arch; 2) the shape of the zygosphenal lip with two distinct lateral lobes and the prominent median lobe; 3) the very short prezygapophyseal processes; 4) the flat haemal keel. The only difference from the extinct genus Texasophis is the presence of the subcotylar tubercles in some cases. Two species of the genus Texasophis have been reported from the European Miocene: Texasophis meini Rage & Holman, 1984 from the middle Miocene (MN 7+8) of La Grive M (Rage & Holman 1984) and Texasophis bohemiacus Szyndlar, 1987 from the lower Miocene (MN 4) of Dolnice (Szyndlar 1987). Texasophis sp. from Vieux Collonges resembles Texasophis meini in the shape of the zygosphenal lip. On the other hand, the relatively narrow haemal keel and straight (in lateral view) subcentral ridges are characteristics of the species Texasophis bohemiacus .

Subfamily NATRICINAE Bonaparte, 1838

Figures

FIG. 6. — Texasophis sp. from the lower/middle (MN 4/5) Miocene of Vieux Collonges, mid-trunk vertebra (FSL 368353); A, lateral view; B, dorsal view; C, ventral view; D, cranial view; E, caudal view. Scale bar: 2 mm.