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 : 423-424

“ Coluber ” cf. caspioides Szyndlar & Schleich, 1993

MATERIAL EXAMINED. — Griesbeckerzell 1a: 2 cervical vertebrae ( BSPG 1997 XIII 519, 520); 19 trunk vertebrae ( BSPG 1997 XIII 521-539). — Griesbeckerzell 1b: 1 trunk vertebra ( BSPG 1997 XIII 540).

LOCALITY. — Griesbeckerzell 1a, 1b.

DESCRIPTION

Cervical vertebrae ( Fig. 7A )

The vertebrae come from the anterior trunk portion because of the presence of hypapophyses, which unfortunately are broken off close to their bases.In lateral view, the neural spine is almost as long as high and its caudal margin overhangs posteriorly. The strongly protruding and postero-laterally directed diapophysis is clearly separated from the somewhat shorter parapophysis. The distal tip of the short parapophyseal processes is directed anteriorly.The preserved base of the hypapophysis indicates a postero-ventral direction. The small lateral foramina are situated close below the prominent interzygapophyseal ridges.

In dorsal view, the vertebra displays a wide zygosphene. The cranial margin of the zygosphene is somewhat convex and possesses distinct lateral lobes (BSPG 1997 XIII 519), or is concave with a wide median notch ( Fig. 7A ). Prezygapophyseal articular facets are broadly oval. Prezygapophyseal processes are short (less than ½ of the prezygapophyseal facets length) with a pointed tip.

In ventral view,the distal end of the parapophyseal processes is blunt.Small but distinct subcotylar tubercles occur at the sides of the base of the cotylar rim. Subcentral foramina are small.The postzygapophyseal articular facets are subsquare in shape and somewhat enlarged laterally.

In cranial view, the neural arch is vaulted and the neural canal large and rounded with shallow lateral sinuses. The cranial margin of the zygosphenal rim is slightly dorsally arched; however, the middle portion is slightly bent in ventral direction. Prezygapophyses are horizontal. Paracotylar foramina are developed within deep depressions at both sides of the rounded cotyle. A shallow paracotylar notch between parapophyseal process and cotylar rim occurs on both sides of the rounded cotyle.

In caudal view, the zygantral area is large. The condyle is rounded.

Trunk vertebrae ( Fig. 7B )

All vertebrae are very fragmentary. In lateral view, the largest vertebra (cl = 7.32 mm; naw = 6.27 mm; cl/naw = 1.17) has distinct lateral foramina situated just below the prominent interzygapophyseal ridges. The synapophyses (strongly damaged in all specimens) are clearly divided into para- and diapophysis. The anterior end of the haemal keel is not steeply terminated. Although the neural spine is broken off in most specimens, the completely preserved neural spine of one posterior trunk vertebra of a subadult specimen documents that the anterior border was inclined anteriorly and the posterior border inclined posteriorly.

In dorsal view, the zygosphenal lip of the largest vertebrae shows a distinct and wide median notch that is less well expressed in one fragmentary specimen. In posterior trunk vertebrae a small indistinct median lobe may be present on the zygosphene instead of a notch. Prezygapophyseal articular facets are oval and elongated. Although the long prezygapophyseal processes are damaged in most specimens, the fragmentary right prezygapophyseal process of the largest vertebra most probably was long.

In ventral view, distinct subcotylar tubercles may be present on both sides of the ventral margin of the cotylar rim. Deep paracotylar notches occur between the subcotylar tubercles and the base of parapophyseal processes.The subcentral grooves are shallow in mid trunk vertebrae, but the subcentral grooves of posterior trunk vertebrae are deep and narrow. Subcentral foramina are usually very small; they may even be absent in some specimens. The ventral margin of the haemal keel is usually sharp and possesses a cuneate caudal tip; however, in the largest specimen the haemal keel is widened in caudal direction and very flat, and thus this specimen probably represents a posterior trunk vertebra. The postzygapophyseal articular facets are subsquarish in shape.

In cranial view, the neural arch is moderately vaulted and the neural canal is rounded with small lateral sinuses. The cranial margin of the zygosphene is dorsally arched; in the largest specimen the zygosphenal lip is roof-like. The distinct shallow paracotylar notches are visible between the subcotylar tubercles and parapophyseal processes. Tiny paracotylar foramina are situated in very deep narrow depressions on both sides of the cotyle. The ventral margin of the cotylar rim is nearly straight.

In caudal view, the zygantral area is large; a small left parazygantral foramen has been observed only in the largest specimen. The rounded condyle is ventrally slightly depressed. Measurements are as follows (n = 6): cl: or = 4.82-7.32 mm; naw: or = 3.19-6.27 mm; cl/naw: or = 1.17-1.51, mean 1.35 ± 0.13.

DISCUSSION

Vertebrae of colubrine snakes are relatively uniform in structure, and thus identification of fragmented specimens often remains problematic. The largest trunk vertebra from Griesbeckerzell 1a belong to a relatively large animal. In total four different largesized extinct species have been documented from the European Early and Middle Miocene: Coluber suevicus (Fraas, 1870) , Coluber dolnicensis Szyndlar, 1987 , Coluber caspioides Szyndlar & Schleich, 1993 , and Coluber pouchetii (Rochebrune, 1880) . Large-sized colubrines of the suevicus-dolnicensiscaspioides-pouchetii fossil group may be assigned (see Szyndlar 2009: 58) to the genus Hierophis Fitzinger, 1834 (sensu Schätti & Utiger 2001); we therefore agree with Szyndlar (2009) who proposed to use the traditional generic name “ Coluber ” in quotation marks. The type material of Coluber suevicus from the German Middle Miocene (Late Badenian) Steinheim a. Albuch site ( Rage 1984a; Szyndlar & Böhme 1993) is poorly understood, and was only briefly described by Rage (1984a) and figured by Szyndlar & Böhme (1993). Colubrines from the Early Miocene (early Eggenburgian) of Merkur-North have been interpreted ( Ivanov 2002a) as belonging to “ Coluber ” suevicus based on a comparison with two specimens figured by Szyndlar ( Szyndlar & Böhme 1993; Fig. 7 ), but the remarkable interzygapophyseal constriction of vertebrae with a relatively narrow vertebral centre, together with a short and blunt prezygapophyseal processes in the Bohemian material, suggest that they may belong to a different genus (Ivanov pers. obs.). Large colubrines from Griesbeckerzell 1a and 1b differ from “ Coluber ” suevicus in having distinctly larger prezygapophyseal processes and a distinct median notch on the cranial margin of the zygosphene (the incipient notch is also visible in one cervical vertebra; BSPG 1997 XIII 520) instead of a straight zygosphenal lip in dorsal view. The large colubrines from Griesbeckerzell 1a and 1b most probably belong to “ Coluber ” caspioides (type locality Petersbuch 2, Germany); they resemble the above mentioned species in having: 1, a similar length of the prezygapophyseal processes; 2, a moderately vaulted neural arch of the trunk vertebrae; 3, a median notch on the zygosphene in most of the vertebrae; 4, the same shape of the neural spine and the same postero-ventral direction of the hypapophysis in cervical vertebrae. However, all vertebrae are fragmentary and specific assignment therefore remains provisional. The possible synonymy of “ Coluber ” caspioides with “ Coluber ” dolnicensis has been discussed by Szyndlar (1998, 2005). The most characteristic morphological feature of the “ Coluber ” dolnicensis vertebrae is the distinct “step in the anterior portion of haemal keel” in trunk vertebrae (according to Szyndlar 1987: fig. 8B). Moreover, the cranial margin of the zygosphene is usually straight or convex in dorsal view ( Szyndlar 1987: fig. 8C; Ivanov 2002a: fig. 3E 2), which is unlike to the more or less straight zygosphenal lip that is frequently accompanied by a distinct median notch in “ Coluber ” caspioides ( Szyndlar & Schleich 1993: fig. 6E; Ivanov 2002a: fig. 5H). Although “ Coluber ” dolnicensis was originally established based on only two precaudal vertebrae, the more abundant material of vertebrae from the Early Miocene (early Eggenburgian) of Merkur-North, Czech Republic (42 trunk vertebrae) ( Ivanov 2002a) and the late Middle Miocene (Serravallian, MN 7+8) of La Grive M, France (9 trunk vertebrae) ( Ivanov 2002b; pers. obs.) show the same morphology as the type material from Dolnice (early Ottnangian, Szyndlar 1987). As a result, we regard “ Coluber ” dolnicensis and “ Coluber ” caspioides as two separate species.

The distinction of “ Coluber ” caspioides from “ Coluber ” pouchetii (type locality Sansan, Badenian, France) is complicated by the morphology of the trunk vertebrae, and thus remains unresolved. Although Augé & Rage (2000) have defined three vertebral characters of “ Coluber ” pouchetii (i.e. 1) weak convexity of the posterior margin of the neural arch, being almost straight; 2) the lateral compression of the cotyle in numerous vertebrae; and 3) the presence of a small median notch of zygosphene in numerous vertebrae), two of these features (i.e. 1 and 3) also occur in “ Coluber ” caspioides . Moreover, recent studies of the Late Miocene (early Pannonian) cf. “ Coluber ” pouchetii from Rudabánya, Hungary ( Szyndlar 2005) indicate that a dorso-ventral compression of the cotyle may be present ( Szyndlar 2005) instead of a lateral compression, which was mentioned by Augé & Rage (2000). Therefore, the two features suitable to safely distinguishing the trunk vertebrae of “ Coluber ” pouchetii from “ Coluber ” caspioides are: 1) the almost vertical anterior and posterior margins of the high neural spine; and 2) the diapophysis, which is as large as the parapophysis or somewhat larger.

Figures

FIG. 7. — “Coluber” cf. caspioides from the Middle Miocene (MN 6, base) of Griesbeckerzell 1a in lateral (l), dorsal (d), ventral (v), cranial (cr) and caudal (ca) views: A, cervical vertebra (BSPG 1997 XIII 520); B, middle trunk vertebra (BSPG 1997 XIII 533). Abbreviations: dia, diapophysis; pa, parapophysis; pctf, paracotylar foramen; pp, parapophyseal process; for other abbreviations, and see Figures 4 & 6. Scale bars: 2 mm.