Wednesday, January 16, 2013

Ancient Aquatic Snakes from the Middle Eocene of Crimea



Photo by Jim Craig
The superfamily Acrochordoidea includes the extant file snake family Acrochordidae and fossil Cretaceous-Paleogene families Nigerophiidae and Palaeophiidae. All are aquatic snakes, according to their vertebral morphology. The genus Palaeophis has the largest number of species of the Acrochordoidea genera, and includes 13 species and unidentified remains to the species level from the Maastrichtian to the Priabonian.  In Ukraine and Eastern Europe in general, remains of aquatic snakes are known from five vertebrate bearing localities  Ak-Kaya, Bakhchisarai, Prolom (all in Crimea), Sbornaya (Luhansk Province), and Kiev (Kiev Province).

The presence of the vertebrae of aquatic snakes in the Ak-Kaya locality was first mentioned by Bratishko and Udovichenko in 2007. Later, one vertebra of  Palaeophis sp. was described from this locality by Snetkov and Bannikov 2010. In 2010, E.A. Zvonok made an exploratory excavation pit about 500 m to the east from the nummulite limestone quarry of Ak-Kaya and collected six vertebrae of  Palaeophis nessovi. In 2011, E.A. Zvonok excavated the second pit and recovered numerous vertebrae of aquatic snakes. This material is discussed in a new paper by Zvonok and Snetkov (2012).

They  refer the vertebrae to three known species of the genus Palaeophis (P. tamdy, P. nessovi and P. cf. toliapicus). These species demonstrate different degree of aquatic adaptations and lived in a restricted area in the eastern part of the Tethys Ocean during the Middle Eocene.

Palaeophis nessovi has well developed pterapophyses, comparatively short prezygapophyses and strongly laterally compressed posterior and anterior trunk vertebrae. These characters suggest that P. nessovi was well adapted to the  aquatic mode of life .  Palaeophis tamdy has large prezygapophyses and lacks pterapophyses, and is considered less specialized. Palaeophis cf. toliapicus, was most likely adapted to an aquatic life style even better than P. nessovi according to less developed prezygapophyses and stronger lateral compression of the vertebra.

Citation
Zvonok E.A. and P.B. 2012. Snetkov NEW FINDINGS OF SNAKES OF THE GENUS PALAEOPHIS OWEN, 1841 (ACROCHORDOIDEA: PALAEOPHIIDAE) FROM THE MIDDLE EOCENE OF CRIMEA. Proceedings of the Zoological Institute RAS 316:392-400.

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