Natrix sp.

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 : 431-432

Natrix sp.

MATERIAL EXAMINED. — 28 precaudal vertebrae ( BSPG 1997 XIII 570-597); 2 caudal vertebrae ( BSPG 1997 XIII 598, 599).

LOCALITY. — Griesbeckerzell 1a.

DESCRIPTION

Precaudal vertebrae ( Fig. 11 )

In lateral view, the neural spine, dorsally thickened in one specimen, is high, approximately 2 times longer than high. The cranial margin is inclined anteriorly and the caudal margin inclines posteriorly. The interzygapophyseal ridges are well developed. The lateral foramina are small but distinct and situated in shallow depressions. Synapophyses, usually damaged, are faintly separated into para- and diapophyses of about the same length. The straight or very slightly dorsally vaulted subcentral ridges are prominent, even in anterior precaudal vertebrae. The hypapophysis possesses a well developed anterior keel that usually is triangular in the anterior part.

In dorsal view, the cranial margin of the zygosphene usually has a distinct and wide median lobe; a small distinct median notch in the zygosphenal lip is present in the largest fragmentary vertebra. Short and blunt epizygapophyseal ridges are usually developed in the posterior part of the neural arch.The prezygapophyseal articular facets are broadly oval. Prezygapophyseal processes are sometimes preserved, they reach half the length of the prezygapophyseal facet.

In ventral view, the centrum is elongated and the hypapophysis is narrow. Distinct subcotylar tubercles are consistently present on the ventrolateral margins of the cotylar rim. The parapophyseal processes are distinct and their distal tip (usually broken off) is obtuse. The subcentral ridges are well developed and extend almost to the anterior margin of the condyle in posterior precaudal vertebrae.Subcentral grooves are wide and shallow, and are deeper in posterior precaudal vertebrae. The subcentral foramina are minute. The postzygapophyseal articular facets are irregularly shaped or subtriangular.

In cranial view, the neural arch is moderately vaulted; the neural canal is rounded with small lateral sinuses. The zygosphenal lip is straight or slightly vaulted dorsally. Paracotylar foramina occur on either side of the rounded cotyle.

In caudal view,the neural arch is gracile and vaulted; the zygantral area is wide. A single parazygantral foramen usually occurs on either side of the posterior wall of the neural arch.The condyle is rounded or slightly depressed laterally. Measurements are as follows (n = 15): cl: or = 3.53-5.34 mm; naw:or = 2.28-3.22 mm; cl/naw: or = 1.40-1.71, mean 1.57 ± 0.09.

Caudal vertebrae

The only preserved two posterior caudal vertebrae lack the pleurapophyses and haemapophyses due to breakage close to their bases. The neural spine is high with the cranial margin inclined anteriorly and caudal margin inclined posteriorly.

DISCUSSION

The vertebrae can be assigned to the genus Natrix with confidence – the cylindrical vertebral centra are elongated, the neural spines are high and inclined in both anterior (cranial margin) and posterior (caudal margin) direction,subcentral ridges are marked, hypapophysis is narrow, and subcotylar tubercles are well-developed. However, the neural spine in the fossils is generally lower than that documented for Natrix sansaniensis (Lartet, 1851) and N.merkurensis (Ivanov, 2002) , two species from the Miocene( Szyndlar & Schleich 1993; Ivanov 2002a). Although the precaudal vertebrae are similar to those of Natrix rudabanyaensis Szyndlar, 2005 reported from the early Late Miocene of Rudabánya, Hungary ( Szyndlar 2005) with regard to the shape and height of the neural spine, the prezygapophyseal processes are clearly shorter, extending only to about ½ of the prezygapophyseal articular facets length.Moreover, the parapophyseal processes are not as long as those of the type material of Natrix rudabanyaensis (cf. Szyndlar 2005: 39, fig. 5C). A more precise determination was impossible because of the poor preservation of all vertebrae.

Figures

FIG. 11. — Natrix sp. (small form) from the Middle Miocene (MN 6, base) of Griesbeckerzell 1a, in lateral (l), dorsal (d), ventral (v), and cranial (cr) views: A, anterior trunk vertebra (BSPG 1997 XIII 570); B, posterior trunk vertebra (BSPG 1997 XIII 578); C, trunk vertebra (BSPG 1997 XIII 592). Abbreviations: other abbreviations: see Figures 4, 6 & 7. Scale bars: 2 mm.