Natricinae, Bonaparte, 1838

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 : 574-575

Natricinae C

Natricinae C – Ivanov 1997a: 120, fig. 54.

MATERIAL EXAMINED. — 24 trunk vertebrae ( FSL 368869- FSL 368891).

DESCRIPTION

Trunk vertebrae

In lateral view, the neural spine is about two times longer than high, its cranial margin overhangs slightly anteriorly, the posterior overhanging is considerable. The largest vertebrae have the top of neural spine very slightly expanded laterally. The interzygapophyseal ridges are distinct but blunt. Well-perceptible lateral foramina are situated within wide and deep depressions. The subcentral ridges are straight to arched slightly dorsally. The ventral margin of the peculiar hypapophysis is not straight (Ivanov 1997a: fig. 54A), the distal end of the hypapophysis is rounded and directed caudally. The para- and diapophyses are well-separated from each other, the parapophyses are nearly as large as the diapophyses. The parapophyseal processes are short and directed anteriorly rather than antero-ventrally. In dorsal view, the cranial margin of the zygosphene is mostly concave to straight, rarely a wide median lobe may occur. The prezygapophyseal articular surfaces are obovate, the prezygapophyseal processes are not preserved. The epizygapophyseal spines are slightly developed. In ventral view, both the subcentral ridges and grooves are well-developed only in the posterior trunk vertebrae, in the middle trunk vertebrae these structures are not so distinct. The subcentral foramina, situated at the base of the gracile hypapophysis, are minute and hardly perceptible. Subcotylar tubercles often occur on the ventral margin of the cotyle. The postzygapophyseal articular surfaces are irregular. In cranial view, the neural arch is more or less vaulted and the neural canal is rounded with small lateral sinuses. The zygosphenal lip is convex. The parapophyseal processes are separated from the cotyle by shallow furrows. The paracotylar foramina are situated in deep or shallow depressions. The metrical measurements are as follows (n = 8): cl: or = 3.54-4.90; naw: or = 2.25-3.40; cl/naw: or = 1.38-1.63, mean 1.50 + 0.10.

DISCUSSION

Although low (rarely high) neural spine of most vertebrae is broken off at the base, it may be observed that its cranial margin overhangs ante-

A B C

riorly, the caudal margin overhangs posteriorly. This is the most important criterion for the affiliation to the subfamily Natricinae . Based on the height of the neural spine, it is assumed that the Natricinae C may belong to the genus Natrix . However, a peculiar shape of the hypapophysis distinguishes the morphotype Natricinae C from all known representatives of the genus Natrix . Regarding the extinct genus Neonatrix , the morphotype Natricinae C somewhat resembles the new species of this genus from the middle Miocene (MN 6) of the French locality Sansan (Rage pers. comm. 1996; Augé & Rage 2000). However, the shape of the hypapophysis is similar to only one vertebra (Augé & Rage 2000: fig. 25A), while the other vertebrae differ considerably in the shape of the hypapophysis. Moreover, the vertebrae of the new species of Neonatrix (Augé & Rage 2000) are smaller than those of Natricinae C. The Natricinae C differs from the Natricinae A in the following features: 1) the hypapophysis is not straight; 2) the lateral sinuses of the neural canal are small and indistinct. Due to the quite different shape of the hypapophysis, without furrow separating the anterior keel from the remaining hypapophysis, the Natricinae C differs from the Natricinae B.