Micrurus aff. gallicus 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 : 576-577

Micrurus aff. gallicus Rage & Holman, 1984

Micrurus cf. gallicus – Rage & Holman 1984: 99. Micrurus aff. gallicus – Ivanov 1997a: 129, fig. 59. MATERIAL EXAMINED. — 1 trunk vertebra (FSL 369450).

DESCRIPTION

Trunk vertebra ( Fig. 11 )

In lateral view, the neural spine is low, both the cranial and caudal margins overhang caudally. The interzygapophyseal ridges are slightly developed. The lateral foramina are small and not situated in depressions. The subcentral ridges are prominent, extending from the synapophyses to the proximal margin of the condyle. Both the para- and diapophyses are broken off at the base. The hypapophysis is damaged, without its distal tip. In dorsal view, the zygosphene has clearly developed lateral lobes. The median lobe is very wide, thus, the zygosphenal lip is more convex than crenate. The prezygapophyseal articular surfaces are oval, the prezygapophyseal processes are broken off at the base. Epizygapophyseal spines are missing. In ventral view, the hypapophysis extends cranially to the basis of the cotyle where it forms a small and wide tubercle. Both the subcentral ridges and wide subcentral grooves are distinct. The subcentral foramina are very small, located at the base of the hypapophysis. The postzygapophyseal articular surfaces are roughly rounded to irregularly shaped. In cranial view, the neural arch is moderately and regularly vaulted; the neural canal is circular with wide lateral sinuses. The zygosphenal lip is convex. On both sides of the rounded cotyle are situated paracotylar foramina in wide depressions. In caudal view, the postzygapophyseal articular surfaces are tilt- ed upward, the zygantral area is relatively wide. The relatively small condyle is rounded. Small parazygantral foramina are situated above the postzygapophyseal surfaces. The measurements of vertebra are as follows: cl = 3.02; naw = 2.05; width between prezygapophyses (pr-pr) = 3.57; width between postzygapophyses (po-po) = 3.40; distance between pre- a postzygapophyses (pr-po) = 3.47; zygosphenal width (zw) = 1.73; height of cotyle (cth) = 1.09; width of cotyle (ctw) = 1.23.

DISCUSSION

The vertebra was originally referred to as Micrurus cf. gallicus by Rage & Holman (1984),

A B

C

however, without precise description and depiction. The vertebra belongs most probably to a small representative of the family Elapidae on the basis of the low neural spine overhanging posteriorly and the presence of a hypapophysis. Most likely, it represents an adult individual having small dimensions – small diameter of the neural canal, which is as wide as the cotyle (without lateral sinuses). Therefore, the vertebra is assigned to the genus Micrurus . The vertebra is very similar to the extinct species Micrurus gallicus report- ed originally from the French locality La Grive M (MN 7) (Rage & Holman 1984). M. aff. gallicus from Vieux Collonges differs from M. gallicus in the following features: 1) the subcentral ridges are better developed in M. aff. gallicus but this character may be explained by the fact that this vertebra is a posterior trunk one; 2) in cranial view, the zygosphenal lip of M. aff. gallicus is convex while in known representatives of M. gallicus it is straight; 3) M. aff. gallicus has a small distinct tubercle developed on the ventral margin of the cotyle. In case of M. gallicus this tubercle is absent. A denotation “aff.” reflected small mor- phological differences between M. aff. gallicus and M. gallicus .

Figures

FIG. 11. — Micrurus aff. gallicus Rage & Holman, 1984 from the lower/middle (MN 4/5) Miocene of Vieux Collonges, trunk vertebra (FSL 369450); A, lateral view; B, dorsal view; C, ventral view; D, cranial view; E, caudal view. Scale bar: 2 mm.