Neonatrix cf. europaea Rage & Holman, 1984

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 : 568-569

Neonatrix cf. europaea Rage & Holman, 1984

Neonatrix cf. europaea – Rage & Holman 1984: 99. — Ivanov 1997a: 99, fig. 45.

MATERIAL EXAMINED. — 7 trunk vertebrae ( FSL 368823- FSL 368829).

DESCRIPTION

Trunk vertebrae ( Fig. 7 )

In lateral view, the neural spine is about two times longer than high; its cranial margin is vertical or slightly overhangs anteriorly, the caudal margin overhangs posteriorly. The interzygapophyseal ridges are well-developed, however they are not very sharp. Epizygapophyseal spines are lacking. The subcentral ridges are approximately straight and reach the vicinity of the proximal margin of the condyle. The lateral foramina are well-perceptible, they are situated in wide and shallow (rarely deeper) depressions. The para- and diapophyses are clearly separated, the parapophyses are as long as the diapophyses, the antero-ventrally directed parapophyseal processes are relatively short. Mostly broken off hypapophyses were probably very short. In dor-

A B

C

sal view, the zygosphenal lip possesses welldeveloped lateral lobes, the median lobe is wide, thus, the cranial margin of the zygosphene seems convex. In some cases, the median lobe is lacking and, therefore, the shape of the zygosphenal lip is variable. The prezygapophyseal articular surfaces are oval; the thin and pointed prezygapophyseal processes reach about half of the length of the prezygapophyseal surfaces. The neural spine is sharp. In ventral view, both the subcentral ridges and grooves are well-developed, they are distinct especially in the cranial part of vertebrae. In posterior trunk vertebrae these structures extend considerably caudally. The hypapophysis is distinct, narrow and short, the anterior keel expands triangularly in the cranial direction. The subcentral foramina are minute and situated mostly at the base of the hypapophysis. The postzygapophyseal articular surfaces are irregular or approximately drop-like. In cranial view, the neural arch is clearly vaulted, the neural canal is circular like the cotyle. The zygosphenal lip is slightly convex. Relatively deep depressions occur on each side of the cotyle, the small paracotylar foramina are situat- ed in these depressions. The parapophyseal processes are separated from the lateral margins of the cotyle by deep notches.

DISCUSSION

The genus Neonatrix represents a common representative of the subfamily Natricinae in the European Tertiary. At Vieux Collonges, the determination is very difficult because of the limited number of specimens; therefore, a secure assignation at species level is impossible. Recent investigations (Szyndlar unpubl.; see also Discussion about the morphotype Elapidae B) showed that a great amount of representatives of the family Elapidae , closely similar to small natricine snakes, appeared during the Neogene. The only distinguishing character is the relatively high neural spine in natricines. Unfortunately, the neural spine is often broken off at the base, therefore the assignation at the subfamiliar level may be problematical. Therefore, some ophidian paleoherpetologists recommend (Szyndlar pers. comm. 1996) a denotation Natricinae indet. which is less precise but more accurate.

The vertebrae of the genus Neonatrix are characterised by the small dimensions and the short hypapohysis which does not reach the caudal margin of the condyle. Three species of this genus have been discovered in the European Tertiary: Neonatrix europaea Rage & Holman, 1984 , N. crassa Rage & Holman, 1984 (Rage & Holman 1984) and N. nova Szyndlar, 1987 (Szyndlar 1987). Remaining three species, Neonatrix elongata Holman, 1973 , N. magna Holman, 1982 and N. inferna Holman, 1996 were discovered in the middle and the upper Miocene of Nebraska, Texas and South Dakota (Holman 1979, 1982, 1996). N. cf. europaea differs from N. nova in its smaller dimensions and the marked median lobe at the zygosphenal lip. Szyndlar (1987) also considers as distinguishing features the less vaulted neural arch and the rounded cotyle in N. nova. However, it is suggested that such features may also be seen in N. europaea . N. cf. europaea differs from N. crassa in the cranial margin of the zygosphene which is convex in the first mentioned species. Contrary to the North American species N. elongata and N. magna , N. cf. europaea has a more developed hypapophysis and longer prezygapophyseal processes (Rage & Holman 1984). N. inferna differs from N. cf. europaea in the elongate vertebrae and the much more lower neural spine.

Figures

FIG. 7. — Neonatrix cf. europaea Rage & Holman, 1984 from the lower/middle (MN 4/5) Miocene of Vieux Collonges, trunk vertebra (FSL 368827); A, lateral view; B, dorsal view; C, ventral view; D, cranial view; E, caudal view. Scale bar: 2 mm.