Saturday 17 March 2012

A Salamander from the Late Jurassic of China.

The Urodeles (Salamanders and Newts) are an ancient group of amphibians, dating back to at least the Middle Jurassic. Modern Urodeles can be divided into three groups, the Cryptobranchoids (Giant Salamanders), the Salamandroids (Salamanders and Newts) and the Sirenoids (Sirens). The Cryptobranchoids and Salamandroids are thought to have split early in the history of the group, probably within the Jurassic, the taxonomic position of the Sirenoids is less certain.

In a paper in the Proceedings of the National Academy of Sciences on 12 March 2012, Ke-Qin Gao of the School of Earth and Space Sciences at Peking University and Neil Shubin of the Department of Organismal Biology and Anatomy at the University of Chicago, describe a new fossil Salamandroid from the Oxfordian Stage of the Late Jurassic in Liaoning Province.

The new Salamander from Liaoning. Photograph left and explanatory drawing right. Abbreviations: adf, anterodorsal fenestra; at, atlas; bd, branchial denticle; d, dentary; fe, femur; fi, fibula; fr, frontal; hb, hypobranchial; hu, humerus; il, ilium; lac, lacrimal; mx, maxilla; na, nasal; op, operculum; pa, parietal; pal, palatine; prf, prefrontal; pm, premaxilla; pra, prearticular; ps, parasphenoid; pt, pterygoid; qu, quadrate; ra, radius; sc, scapulocoracoid; se, sphenethmoid; sm, septomaxilla; sq, squamosal; sr, sacral rib; st, stapes; ti, tibia; tr, trunk rib; ul, ulna; vo, vomer. From Gao & Shubin (2012).

The specimen was found in a layer of volcanic ash deposited in a lake, with a radiometric age of 157 million years in the Late Jurassic Tiaojishan Formation, making it the oldest known Salamandroid by some 40 million years. The fossil has been named as Beiyanerpeton jianpingensis; Beiyanerpeton meaning 'Creeping animal from Northern Yan' and jianpingensis referring to the location where the fossil was found.

The location and stratigraphic sequence where Beiyanerpeton jianpingensis was found. From Gao & Shubin (2012).

Beiyanerpeton jianpingensis is a medium sized Salamander roughly 100 mm in length, not counting the tail, which is missing. It shows signs of having had external gills, which would be considered neotinous (a juvenile trait carried into adulthood) in modern Salamanders, though there is no means of assessing the maturity of this specimen so the label might not be completely accurate.

Close up photograph of the head of Beiyanerpeton jianpingensis (top) and explanatory drawing (bottom). Abbreviations as above, note structures at back of skull interpreted as external gills. From Gao & Shubin (2012).