Natrix aff. sansaniensis (Lartet, 1851)

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 : 570

Natrix aff. sansaniensis (Lartet, 1851)

Natrix aff. sansaniensis . — Ivanov 1997a: 102, fig. 47.

MATERIAL EXAMINED. — 2 trunk vertebrae ( FSL 368830, FSL 368831).

DESCRIPTION

Trunk vertebrae

In lateral view, the neural spine is unusually high, almost as high as long. Its cranial margin overhangs anteriorly and the caudal margin overhangs caudally. The relatively sharp interzygapophyseal ridges are strikingly developed. The conspicuous lateral foramina are situated in shallow depressions. The subcentral ridges are considerably marked and they are arched dorsally. The para- and diapophyses are well-separated, the posterolaterally directed diapophyses are about as large as the parapophyses. The parapophyseal processes are directed anteriorly. The broken off hypapophyses were distinct and deep. In dorsal view, the zygosphenal lip has distinct lateral lobes and a prominent median lobe, in anterior (rarely in posterior) trunk vertebrae the median lobe may be laterally expanded, thus the zygosphenal lip is almost convex. The prezygapophyseal articular surfaces are circular to oval, the antero-laterally directed prezygapophyseal processes are very long – at least as long as the prezygapophyseal surfaces. The dorsal border of the neural spine is usually expanded. The epizygapophyseal spines are prominent. In ventral view, the subcentral ridges are distinct, however the subcentral grooves are shallow. The subcentral foramina are minute and hardly visible. The anterior keel of the hypapophysis is triangular; very distinct subcotylar tubercles are developed at the ventral margin of the cotyle. The postzygapophyseal articular surfaces are irregularly shaped. In cranial view, the neural arch is weakly vaulted, the neural canal is circular and the zygosphenal lip is straight to slightly convex. The small paracotylar foramina are situated in prominent depressions on both sides of the rounded cotyle.

DISCUSSION

The described shape of the neural spine is characteristic for the genus Natrix . N. sansaniensis differs from all other Natrix species, living and extinct, in its very high neural spine (Szyndlar & Schleich 1993). The following extinct species of the genus Natrix have been reported: Natrix mlynarskii Rage, 1988 (MP 22) (Rage 1988), Natrix sansaniensis (Lartet, 1851) (?MN 4-MN 6) (Rage 1981; Szyndlar & Schleich 1993), Natrix longivertebrata Szyndlar, 1984 (?MN 7+8-MN16) (Szyndlar 1984, 1991a, b), Natrix parva Szyndlar, 1984 (Szyndlar 1984) . The described species is closely related to “ Natrix aff. N. sansaniensis (Lartet, 1851) ” reported from the German lower Miocene (MN 4) locality Petersbuch 2 (Szyndlar & Schleich 1993). A denotation “aff.” has been used because of some morphological resemblance with the extinct species N. mlynarskii Rage, 1988 (Szyndlar & Schleich 1993).