Texasophis cf. meini Rage & Holman, 1984

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 : 430

Texasophis cf. meini Rage & Holman, 1984

MATERIAL EXAMINED. — 1 trunk vertebra ( BSPG 1997 XIII 554).

LOCALITY. — Griesbeckerzell 1a.

DESCRIPTION

Trunk vertebra ( Fig. 10 )

In lateral view, the vertebra is elongated. The base of the missing neural spine indicates that this structure was originally very low. Interzygapophyseal ridges are moderately developed. The lateral foramina are large and do not occur in depressions. The condyle is situated on a relatively long neck. The dorsally arched subcentral ridges are indistinct, but this may also be due to the partial corrosion of the vertebra. Synapophyses are strongly damaged.

In dorsal view, the cranial margin of the zygosphene possesses a distinct median and two lateral lobes. The damaged left prezygapophyseal articular facet was originally oval in shape.

In ventral view, the centrum is elongated. Both the wide and flat haemal keel and subcentral ridges are partially corroded.Subcentral foramina are very small and indistinct. The ventral margin of the cotylar rim lacks subcotylar tubercles.The left postzygapophyseal articular facet is irregularly circular in shape.

In cranial view,the neural arch is slightly vaulted and the neural canal is rounded with large lateral sinuses. The zygosphenal lip is straight.Paracotylar foramina are situated in wide depressions on both sides of the slightly dorso-ventrally depressed cotyle.

In caudal view, the zygantral area is wide; the damaged condyle is slightly dorso-ventrally depressed. Measurements of the vertebra are as follows: cl = 3.83 mm; naw = 2.48 mm; cl/naw = 1.54.

DISCUSSION

Texasophis represents a small-sized colubrine snake. Four of five characteristics ( Holman 1977, 2000) of the genus Texasophis have been observed in the trunk vertebra from Griesbeckerzell 1a: 1) an elongated form of the vertebrae; 2) a moderately vaulted neural arch; 3) a low neural spine; 4) a robust haemal keel; and 5) distinct subcentral grooves and ridges. The subcentral ridges of Texasophis cf. meini from Griesbeckerzell 1a are blunt and indistinct, which is due probably to partial abrasion. The ventrally flattened haemal keel, which becomes slightly narrower in cranial direction, and a distinct median lobe with well developed lateral lobes of the zygosphene are features that have also been described from the type material of Texasophis meini from the French late Middle Miocene of La Grive M ( Rage & Holman 1984). The poorly preserved holotype of Texasophis fossilis from the Middle Miocene (Early Barstovian) of Texas ( Holman 1977; 2000: 192, fig. 122) closely resembles Texasophis meini with regard to the wide haemal keel. However, it differs from Texasophis meini by the presence of a distinctly shallower notch in the posterior border of the neural arch (cf. Holman 1977, 1979, 2000). The variable width of the haemal keel observed in antero-posterior direction of the holotype of Texasophis fossilis is probably a result of the poor state of preservation, but intracolumnar variability may also have existed with regard to this feature (Ivanov, personal observation of Texasophis meini from La Grive L7 and M).

Figures

FIG. 10. — Texasophis cf. meini from the Middle Miocene (MN 6, base) of Griesbeckerzell 1a; middle trunk vertebra (BSPG 1997 XIII 554), in lateral (l), dorsal (d), ventral (v), and cranial (cr) views. Abbreviations: see Figures 4 & 7. Scale bar: 2 mm.