Odontochelys

Fossil of Odontochelys

• Guizhou (China)

Odontochelys semitestacea > Li et al., 2008

Odontochelys is an extinct genus of turtles ( Testudinata ) from the Upper Triassic of China.

To date, the type species O. semitestacea is only described scientifically in the only genus of the taxon Odontochelyidae. Odontochelys is the oldest and possibly most primitive turtle known to date.

Naming

The name of the genus is derived from Greek odonto - "tooth" and chelys "turtle", the epithet from the Latin prefix semi-" half" and testaceus " armored ". The name therefore means approximately " dentulous turtle with half tank."

Features

The type specimen is kept in the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences under the archive number V 15639; the first description also referred to two other finds of the same species ( IVPP V 13240 and IVPP V 15653 ).

The approximately 40 cm fossil was discovered in southwest China's Guizhou Province about 220 million year old sediments of the coastal area of sea from the Upper Triassic. In the original description it was described as particularly original in terms of the anatomy of the bone armor, ( " primitive more " ) as the original in comparison to also derived from the Upper Triassic genus Proganochelys. In contrast to the extant turtles upper and lower jaw of the animal were dentate. The plastron ( plastron ) was fully developed, but not the carapace ( carapace ), only the ribs were already widened. Thereof connected Li et al. 2008 that has developed in the course of the phylogeny of turtles in the ventral tank outside the carapace. This sequence is consistent with the course of embryogenesis of today's turtles.

Against this interpretation of the fossil evidence reported Reisz et al. But in 2008 already parallel to the first description in the journal Nature on concerns. One could also argue, due to the locality on the edge of a sea or in a river delta that Odontochelys semitestacea have already possessed a carapace, this however - was so little ossified that he had not survived - as with the recent marine soft-shelled turtles. This would mean that the lack of carapace is not original ( plesiomorphes ) feature in this type, but already a modification ( apomorphy ) compared to even older, previously unknown precursor species with a hard carapace.