''Proterochersis'' is an extinct genus of

turtle Turtles are an order of reptiles known as Testudines, characterized by a special shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Cryptodira (hidden necked t ...

from the

Late Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. ...

period ( Norian stage) of

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located entirel ...

. It is known from a large number of fossils uncovered in

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...

and

Poland Poland, officially the Republic of Poland, is a country in Central Europe. It is divided into 16 administrative provinces called voivodeships, covering an area of . Poland has a population of over 38 million and is the fifth-most populou ...

.Fraas E (1913)
"''Proterochersis'', eine pleurodire Schildkröte aus dem Keuper"
''Jahreshefte des Vereins für Vaterländische Naturkunde in Württemberg'' 69: p. 13–30Szczygielski T & Sulej T (2016). "Revision of the Triassic European turtles ''Proterochersis'' and ''Murrhardtia'' (Reptilia, Testudinata, Proterochersidae), with the description of new taxa from Poland and Germany". ''Zoological Journal of the Linnean Society'' 177(2): pp. 395–427. Szczygielski1 T, Słowiak J & Dróżdż1 D (2018). "Shell variability in the stem turtles ''Proterochersis'' spp". ''PeerJ'' 6: The genus was named from fossil remains from

in 1913 by Fraas, who recognized two species: ''P. robusta'' (type species) and ''P. intermedia''. Since then, Szczygielski and Sulej have found that the differences described by Fraas could be the result of intraspecific variation, meaning that ''P. intermedia'' are synonymous with ''P. robusta''. They also decided to classify more recent fossil findings from

as two new species, ''P. limendorsa'' and ''P. porebensis''. A study from 2021 concluded that fossil turtle remains described in 1865 as ''Chelytherium obscurum'' are probably synonymous with ''Proterochersis''.Szczygielski T. (2021). "Obscure by name: solving the enigma of ''Chelytherium obscurum'', the first described Triassic turtle". ''Zoological Journal of the Linnean Society'' 192(4): pp. 1111–1122. Generally, the rules of

nomenclature Nomenclature (, ) is a system of names or terms, or the rules for forming these terms in a particular field of arts or sciences. The principles of naming vary from the relatively informal conventions of everyday speech to the internationally ag ...

advocate that the oldest taxonomic name should replace more recent ones, but Szczygielski choose to keep the name ''Proterochersis''.

Description

Together with ''

Proganochelys ''Proganochelys'' is an extinct, primitive stem-turtle that has been hypothesized to be the sister taxon to all other turtles creating a monophyletic group, the ''Casichelydia''. ''Proganochelys'' was named by Georg Baur in 1887 as the oldest tur ...

'', ''Proterochersis'' is one of the earliest known Testudinata with a fully formed shell. Fossils show that ''Proterochersis'' was a turtle of moderate size, with a domed shell similar to modern

tortoise Tortoises () are reptiles of the family Testudinidae of the order Testudines (Latin: ''tortoise''). Like other turtles, tortoises have a shell to protect from predation and other threats. The shell in tortoises is generally hard, and like oth ...

s. The shell reached a length of about in the largest known specimens. The shell also possesses a well developed caudal notch in the back end, indicating that ''Proterochesis'' might have possessed a fairly well developed tail, similar to modern

snapping turtle The Chelydridae is a family of turtles that has seven extinct and two extant genera. The extant genera are the snapping turtles, ''Chelydra'' and '' Macrochelys''. Both are endemic to the Western Hemisphere. The extinct genera are '' Acherontem ...

Phylogeny

''Proterochersis'' belongs to the Proterochersidae, which represent the oldest and most basal of all known shelled turtles (

testudinata Testudinata is the group of all tetrapods with a true turtle shell. It includes both modern turtles (Testudines) and many of their extinct, shelled relatives (stem-turtles). Though it was first coined as the group containing turtles by Jacob The ...

ns). Some studies in the 2010s suggested that they belong to the crown-group of turtles, as ''Proterochersis'' possess several anatomical features in common with modern side-necked turtles (pleurodires). If ''Proterochersis'' were indeed a pleurodiran, this would mean that the crown-group of turtles originated in the Late Triassic period. More detailed research, however, concludes that the similarities with modern turtles are the result of convergent evolution and that the crown group of turtles dates back no further than to Middle Jurassic.Joyce W.G., Schoch R.R. & Lyson T.R. (2013). "The girdles of the oldest fossil turtle, ''Proterochersis robusta'', and the age of the turtle crown". ''BMC Evolutionary Biology'' 13: 266. Szczygielski and Sulej found ''Proterochersis'' to be more primitive than ''

''.

Paleoecology

There are disagreement about the lifestyle of ''Proterochersis''. while histological data have indicated a terrestrial lifestyle,Scheyer T.M. & Sander P.M. (2007). “Shell bone histology indicates terrestrial palaeoecology of basal turtles”. ''Proceedings of the Royal Society B'' 274(1620): p. 1885–1893: other evidence suggest that it was aquatic.Bajdek P ''et.al.'' (2019). "Bromalites from a turtle-dominated fossil assemblage from the Triassic of Poland". ''Palaeogeography, Palaeoclimatology, Palaeoecology'' 520: p. 214–228.

References

External links

''Proterochersis''
at the

Paleobiology Database The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms. History The Paleobiology Database (PBDB) originated in the NCEAS-funded Phanerozoic Marine Pale ...

.
Life restoration of ''Proterochersis'' from bajdek ''et.al.'' 2019
{{Taxonbar, from=Q21941971 Late Triassic reptiles of Europe Prehistoric reptile genera Fossil taxa described in 1913 Testudinata