Coluber

Ivanov, Martin & Böhme, Madelaine, 2011, Snakes from Griesbeckerzell (Langhian, Early Badenian), North Alpine Foreland Basin (Germany), with comments on the evolution of snake faunas in Central Europe during the Miocene Climatic Optimum, Geodiversitas 33 (3), pp. 411-449 : 428-429

“ Coluber ” sp.

MATERIAL EXAMINED. — 3 trunk vertebrae ( BSPG 1997 XIII 551-553).

LOCALITY. — Griesbeckerzell 1a.

DESCRIPTION

Trunk vertebrae ( Fig. 9 )

In lateral view, the best preserved vertebra (BSPG 1997 XIII 551) shows distinct and sharp interzygapophyseal ridges. The cranial margin of partially preserved neural spine originates in the middle of the zygosphene length. The neural spine extends to the posterior border of the neural arch. Small but distinct processes (well visible also in cranial view) are developed at bases of the lateral facets of the zygosphene. Large lateral foramina are distinct and situated close to the prezygapophysis and below the interzygapophyseal ridges. The haemal keel is deep, subcentral ridges are prominent and extend as far as to the vicinity of the anterior border of the condyle. The condyle is positioned on a relatively long neck. Para- and diapophyses are damaged; the left synapophysis of the best preserved vertebra shows that the diapophysis was somewhat dorsoventrally longer than the parapophysis.

In dorsal view, the prezygapophysis is separated from the postzygapophysis by a distinct constriction; as a result, the vertebra is X-shaped. The right prezygapophysis of the best preserved vertebra (BSPG 1997 XIII 551) is characterized by a prezygapophyseal articular facet that is subtriangular to roughly sigmoid in shape; the prezygapophyseal process reaches about ½ of the prezygapophyseal facet length. The zygosphene is convex and has distinct lateral lobes.

In ventral view, the synapophysis is indistinctly divided into a dia- and parapophysis, but this may be also a result of surface damage. The parapophyses are short. The haemal keel is sharp; its ventral margin is flattened in one of the posterior trunk vertebrae. The subcentral ridges are well developed, especially in the anterior part of the vertebra, and the subcentral grooves are relatively short. The large subcentral foramina are situated in the anterior half of the vertebral centrum, roughly at the level

ct

of the maximum of interzygapophyseal constriction. Postzygapophyseal articular facets, irregular in shape, originally were laterally enlarged.

In cranial view, the neural arch is weakly vaulted and the neural canal is rounded. The preserved right prezygapophysis is slightly tilted up dorsally. Paracotylar foramina are situated at both sides of the slightly dorsoventrally depressed cotyle.

In caudal view, the zygantral area is gracile and the neural arch is weakly vaulted. Both postzygapophyseal articular facets are tilted up dorsally.Two parazygantral foramina on the left side, as well as the one on the right side, are positioned close to the dorsal margin of the neural arch. The condyle is rounded. Measurements are as follows (n = 3): cl: or = 3.00- 3.27 mm; naw: or = 2.33-2.88 mm; cl/naw: or = 1.14-1.29, mean 1.23 ± 0.08.

DISCUSSION

The presence of paracotylar foramina and a haemal keel in trunk vertebrae, together with the small dimensions, indicates that the material belongs to a small colubrine snake. The vertebrae resemble Coluber hungaricus reported from the Late Miocene ( Venczel 1994, 1998; Szyndlar 2005) and Early Pliocene ( Venczel 2001) of Hungary and from the Middle Miocene of Germany in: 1) the shape of the zygosphenal lip; and 2) the shape of the distally pointed prezygapophyseal processes. These features correspond to those seen in the extant Coluber gemonensis ( Hierophis gemonensis sensu Schätti & Utiger 2001 ), with the exception of the distal tips of the prezygapophyseal processes, which are not pointed in Coluber gemonensis according to Venczel (1994). However, “ Coluber ” sp. from Griesbeckerzell 1a differs from both Coluber gemonensis and Coluber hungaricus in: 1) the shape of the postzygapophyseal articular facets that are strongly enlarged in lateral direction; 2) the shallow indentation of the posterior margin of the neural arch in dorsal view; 3) the prominent subcentral ridges (at least in anterior half of the vertebrae); 4) the presence of small but distinct tubercles at the base of the zygosphenal facets. The relative length of the vertebral centrum depends on the position of the vertebra in the vertebral column – the shortest vertebrae typically occur in the posterior-most trunk section, immediately before the cloacal section ( Hoffstetter & Gasc 1969; Szyndlar 1984). The above mentioned features suggest that the fossils represent a new and distinct species; however, the limited number of vertebrae does not allow for studies of the intracolumnar variations among the small colubrines from Griesbeckerzell 1a and 1b.

Figures

FIG. 9.— “Coluber” sp. from the Middle Miocene (MN 6, base) of Griesbeckerzell 1a; middle trunk vertebra (BSPG 1997 XIII 551) in lateral (l), dorsal (d), ventral (v), and cranial (cr) views. Abbreviations: see Figures 4 & 7. Scale bar: 2 mm.