Proterochersis

Proterochersis
Temporal range: Late Triassic
Fossil remains of Proterochersis shell
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Pantestudines
Clade: Testudinata
Genus: †Proterochersis
Fraas, 1913
Species
  • †Proterochersis intermedia? Fraas, 1913
  • †Proterochersis limendorsa Szczygielski & Sulej, 2016
  • †Proterochersis porebensis Szczygielski & Sulej, 2016
  • †Proterochersis robusta Fraas, 1913
Synonyms
  • Chelytherium obscurum Meyer, 1865[1]
  • Proterochersis robustum Fraas, 1913 [sic]

Proterochersis is an extinct genus of turtle from the Late Triassic period (Norian stage) of Europe. It is known from a large number of fossils uncovered in Germany and Poland.[2][3][4] The genus was named from fossil remains from Germany in 1913 by Fraas, who recognized two species: P. robusta (type species) and P. intermedia.[2] 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 Poland as two new species, P. limendorsa and P. porebensis.[3] A study from 2021 concluded that fossil turtle remains described in 1865 as Chelytherium obscurum[1] are probably synonymous with Proterochersis.[5] Generally, the rules of nomenclature advocate that the oldest taxonomic name should replace more recent ones, but Szczygielski choose to keep the name Proterochersis.[5]

Description

Artistic depiction of Proterochersis in Late Triassic habitat

Together with Proganochelys, Proterochersis is one of the earliest known Testudinata with a fully formed shell.[6] Fossils show that Proterochersis was a turtle of moderate size, with a domed shell similar to modern tortoises. The shell reached a length of about 38.5–40 cm (15.2–15.7 in) in the largest known specimens.[3][6] The shell also possesses a well developed caudal notch in the back end,[3] indicating that Proterochesis might have possessed a fairly well developed tail, similar to modern snapping turtles.[7]

Phylogeny

Shell cast of P. robusta

Proterochersis belongs to the Proterochersidae, which represent the oldest and most basal of all known shelled turtles (testudinatans). 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.[8][6] Szczygielski and Sulej found Proterochersis to be more primitive than Proganochelys.[3][6]

Paleoecology

There are disagreement about the lifestyle of Proterochersis. while histological data have indicated a terrestrial lifestyle,[9] other evidence suggest that it was aquatic.[7]

References

  1. ^ a b Meyer H (1865). "Reptilien aus dem Stubensandstein des oberen Keupers (Dritte Folge)". Palaeontographica 14(3): p. 99–124
  2. ^ a b Fraas E (1913). "Proterochersis, eine pleurodire Schildkröte aus dem Keuper". Jahreshefte des Vereins für Vaterländische Naturkunde in Württemberg 69: p. 13–30
  3. ^ a b c d e Szczygielski 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. doi:10.1111/zoj.12374
  4. ^ Szczygielski1 T, Słowiak J & Dróżdż1 D (2018). "Shell variability in the stem turtles Proterochersis spp". PeerJ 6: doi:10.7717/peerj.6134
  5. ^ a b 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. doi:10.1093/zoolinnean/zlaa139
  6. ^ a b c d Hans-Dieter Sues (August 6, 2019). The Rise of Reptiles. 320 Million Years of Evolution. Johns Hopkins University Press. pp. 50–51. ISBN 9781421428680.
  7. ^ a b Bajdek P et.al. (2019). "Bromalites from a turtle-dominated fossil assemblage from the Triassic of Poland". Palaeogeography, Palaeoclimatology, Palaeoecology 520: p. 214–228. doi:10.1016/j.palaeo.2019.02.002
  8. ^ 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. doi:10.1186/1471-2148-13-266
  9. ^ 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: doi:10.1098/rspb.2007.0499