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 : 571-572

Natricinae A

Natricinae A – Ivanov 1997a: 117-119, fig. 52.

MATERIAL EXAMINED. — 3 cervical vertebrae ( FSL 368832- FSL 368834), 32 trunk vertebrae ( FSL 368835- FSL 368837; FSL 368838- FSL 368866).

DESCRIPTION

Cervical vertebrae ( Fig. 8 A-E)

All preserved vertebrae are very fragmentary. Most likely, the broken off neural spines were originally high. In lateral view, the interzygapophyseal ridges are distinct and the epizygapophyseal spines are under-developed. The lateral foramina are small, but generally well visible and they are situated in shallow depressions. The subcentral ridges are distinct, long and slightly arched dorsally. The bases of the hypapophyses are wide; the hypapophyses were most probably relatively long, which is demonstrated by the long hypapophyses of trunk vertebrae. In dorsal view, the cranial margin of the fragmentary zygosphene possesses distinct lateral lobes and a wide median lobe. The prezygapophyseal articular surfaces were originally oval; the prezygapophyseal processes are broken off. In ventral view, both the subcentral ridges and the wide subcentral grooves are well-developed, the subcentral foramina are minute and hardly visible. The hypapophysis is narrow and the anterior keel expands in the vicinity of the ventral margin of the cotyle. The small subcotylar tubercles are very distinct. The postzygapophyseal articular surfaces are irregular. In cranial view, the neural arch is prominently vaulted, the neural canal is circular (a large calibre documents subadult specimen) and the zygosphenal lip is convex. The minute paracotylar foramina occur in depressions on both sides of the rounded cotyle.

Trunk vertebrae ( Fig. 8 F-J)

In lateral view, the neural spine is about two times longer than high. The cranial margin of the neural spine clearly overhangs anteriorly, the caudal margin overhangs posteriorly. A dorsal expansion of the neural spine does not occur. The interzygapophyseal ridges are mostly well- developed, however, they are not sharp. The epizygapophyseal spines are usually very indistinctly developed. Mostly well-visible lateral foramina are situated in shallow depressions. Both the subcentral ridges and grooves are less developed in anterior trunk vertebrae; in lateral view, they are almost straight. The hypapophysis is relatively long, straight and directed posteroventrally. Its caudally directed distal tip is slightly rounded to pointed. Mostly damaged para- and diapophyses are well-separated from each other; the parapophyseal processes are short and directed antero-ventrally or anteriorly. In dorsal view, the lateral lobes of the zygosphenal lip are developed better than the wide median lobe which is often missing. Thus, the cranial margin of the zygosphene may be concave. The prezygapophyseal articular surfaces are oval, rarely preserved prezygapophyseal processes are thin and pointed. In ventral view, both the subcentral ridges and the relatively wide subcentral grooves are well-developed. The subcentral foramina are often very small. The anterior keel of the hypapophysis expands clearly in cranial direction, the distinct subcotylar tubercles are developed under the ventral margin of the cotyle. In cranial view, the neural arch is vaulted, the neural canal is approximately circular with distinct lateral sinuses and the zygosphenal lip is straight or convex. The notches between parapophyseal processes and the lateral margins of cotyle are not deep, the paracotylar foramina occur on both sides of the cotyle in more or less developed depressions. The metrical measurements are as follows (n = 15): cl: or = 3.83-4.95; naw: or = 2.80-3.47; cl/naw: or = 1.37-1.59, mean 1.46 + 0.07.

DISCUSSION

The presence of a high neural spine whose cranial margin is anteriorly overhanging, the distinct haemal keel and the lateral foramina situated in shallow depressions, support the assignment to the subfamily Natricinae . The distinct hypapophyses extending often behind the distal end of the condyle and the relatively large dimensions of the vertebrae exclude the assignment to the

A B C D

genus Neonatrix . The shape of the relatively high neural spine and the shallow triangular anterior keel exclude the referral to the genus Palaeonatrix (Szyndlar in M~ lynarski et al. 1982; Szyndlar 1987). The morphotype Natricinae A most probably belongs to the genus Natrix , which is supported by the shape of the neural spine and the hypapophysis and by the dimensions of the vertebrae. The morphotype Natricinae A differs from the oldest representative – Natrix mlynarskii Rage, 1988 (MP 22) – especially in the shape of the subcentral ridges which are straight in lateral view and slightly medially bent in ventral view (Rage 1988). It differs from Natrix sansaniensis (Lartet, 1851) in the lower neural spine and absence of blunt ridges extending from the base of the neural spine to each prezygapophysis (Rage 1981). Rage (1984) assumes that the above mentioned ridges occur also in some living taxa. Szyndlar & Schleich (1993) consider the height of the neural spine as the crucial character for the affiliation to the extinct Natrix sansaniensis (Lartet, 1851) . The morphotype Natricinae A differs from Natrix longivertebrata Szyndlar, 1984 in smaller dimensions, the lower ratio cl/naw, and pointed distal tip of the hypapophysis.

Figures

FIG. 8. — Natricinae A from the lower/middle (MN 4/5) Miocene of Vieux Collonges; A-E, cervical vertebra (FSL 368834); A, lateral view; B, dorsal view; C, ventral view; D, cranial view; E, caudal view; F-J, trunk vertebra (FSL 368855); F, lateral view; G, dorsal view; H, ventral view; I, cranial view; J, caudal view. Scale bar: 2 mm.