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 : 572-574

Natricinae B

Natricinae B – Ivanov 1997a: 119-120, fig. 53.

MATERIAL EXAMINED. — 2 trunk vertebrae ( FSL 368867, FSL 368868).

A B

C

DESCRIPTION

Trunk vertebrae ( Fig. 9 )

In lateral view, the neural spine is relatively low (the distinct subcentral ridges and grooves show that this specimen is most probably a posterior trunk vertebrae), its cranial margin overhangs anteriorly and the caudal margin overhangs caudally. The blunt interzygapophyseal ridges are well-developed. The subcentral ridges are long, only slightly arched dorsally. The hypapophysis is broken off in the vicinity of its base which is unusually wide in lateral view. The lateral foramina are distinct and large, in one vertebra the foramina occur in wide depressions. The para- and diapophyses are indistinctly separated, the damaged diapophyses were probably larger than the parapophyses. The damaged parapophyses were shifted under the vertebral centrum, the parapophyseal processes were most likely short. The aliform processes extend behind the caudal margin of the postzygapophyseal surfaces. In dorsal view, the vertebrae are characterised by the long and relatively narrow vertebral constriction. The zygosphenal lip possesses distinct lateral lobes, the median lobe does not protrude strikingly and is very wide. The prezygapophyseal articul-ar surfaces are oval to subtriangular, the prezygapophyseal processes reach about two-thirds of the length of the prezygapophyseal surfaces, they are pointed but relatively massively built. Epizygapophyseal spines are lacking. The diapophyses are directed clearly postero-laterally. In ventral view, the subcentral ridges are sharp, the subcentral grooves are prominently wide. The small subcentral foramina occur at the base of the hypapophysis. The hypapophysis is expanded proximally into a triangular anterior keel which is inclined antero-ventrally. The anterior keel is separated from the remaining hypapophysis by a prominent furrow. In cranial view, the neural arch is slightly vaulted, the neural canal is approximately circular and the zygosphenal lip is convex. The distinct paracotylar foramina are situated in deep depressions on either side of the rounded cotyle. The deep grooves between damaged parapophyseal processes and the margin of cotyle are separated from the depressions with paracotylar foramina by peculiar sharp bony bar. The subcotylar tubercles are lacking or very slightly developed. Metrical measurements: larger vertebra: cl = 4.72; naw = 3.04; cl/naw = 1.55; smaller vertebra: cl = 4.37; naw = 2.92; cl/naw = 1.50.

DISCUSSION

The morphotype Natricinae B is defined by the shape of the hypapophysis with prominent anteri- or keel, which is separated form the remaining hypapophysis by a considerable furrow. The hypapophysis was well-developed and probably relatively deep. This feature helps to distinguish the morphotype Natricinae B from the genus Neonatrix . However, it is impossible to recognize unambiguously whether Natricinae B belongs to Palaeonatrix or Natrix . The morphotype Natricinae B possesses the following features which are characteristic of the genus Palaeonatrix : 1) the hypapophysis markedly extend anteriorly as a keel; 2) the subcentral ridges are prominent (especially in one vertebra). Szyndlar (in M~lynarski et al. 1982; Szyndlar 1987) mentioned that the neural spine of the genus Palaeonatrix is low, however, the study at the locality Petersbuch 2 (Szyndlar & Schleich 1993) showed that also high neural spines may occur in this genus. The morphotype Natricinae B is most similar to the species Palaeonatrix silesiaca Szyndlar, 1982 which is only known (Szyndlar in M~lynarski et al. 1982) from the type locality Opole 2, Poland (MN 7). The morphotype Natricinae B differs from the extinct species of Natrix in the prominent anterior keel; thus, the Natricinae B differs from Natrix longivertebrata Szyndlar, 1984 . From the species Natrix mlynarskii Rage, 1988 the morphotype Natricinae B differs also in the considerably narrow constriction between the prezygapophyses and the postzygapophyses. The Natricinae B differs from Natrix sansaniensis (Lartet, 1851) in the much more lower neural spine – it is about two to three times longer than high. The morphotype Natricinae B differs from the Natricinae A in indistinct subcotylar tubercles. The anterior keel of the hypapophysis is separated from the remaining hypapophysis by a considerable furrow – this feature makes the Natricinae B distinguishable from all remaining morphotypes ( Natricinae A, C & D).

Figures

FIG. 9. — Natricinae B from the lower/middle (MN 4/5) Miocene of Vieux Collonges; A-D, posterior trunk vertebra (FSL 368867); A, lateral view; B, dorsal view; C, ventral view; D, cranial view; E, posterior trunk vertebra (FSL 368868), lateral view. Scale bar: 2 mm.