''Proterochersis'' is an extinct genus of

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

from the

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

period (

Norian The Norian is a division of the Triassic geological period, Period. It has the rank of an age (geology), age (geochronology) or stage (stratigraphy), stage (chronostratigraphy). It lasted from ~227.3 to Mya (unit), million years ago. It was prec ...

stage) of

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

. 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 lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...

and

Poland Poland, officially the Republic of Poland, is a country in Central Europe. It extends from the Baltic Sea in the north to the Sudetes and Carpathian Mountains in the south, bordered by Lithuania and Russia to the northeast, Belarus and Ukrai ...

.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 theoretical field studying nomenclature is sometimes referred to as ''onymology'' or ''taxonymy'' ). The principl ...

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 a genus of extinct, primitive stem-turtle. ''Proganochelys'' was named by Georg Baur in 1887 as the oldest turtle in existence at the time. The name ''Proganochelys'' comes from the Greek language, Greek word ''ganos'' meani ...

'', ''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 for "tortoise"). Like other turtles, tortoises have a shell to protect from predation and other threats. The shell in tortoises is generally hard, and like o ...

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 turtles.

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 excluding ''Odontochelys'' and ''Eorhynchochelys,'' which are pla ...

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.
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