Pleurosternon
Temporal range: Tithonian–Berriasian
Pleurosternon (ovatum) bullocki fossil
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Testudines
Family: Pleurosternidae
Genus: Pleurosternon
Owen, 1853
Species
  • P. bullocki (Owen, 1842) (type)
  • P. moncayensis Pérez-Garcia, 2021

Pleurosternon is an extinct genus of freshwater pleurosternid turtle from the late Jurassic period to the early Cretaceous period of Europe.[1] Its type species, P. bullocki was described by the paleontologist Richard Owen (noted for coining the word Dinosauria) in 1853. Since then, and throughout the late 19th century, many fossil turtles were incorrectly assigned to this genus, though only two are currently considered valid.

Taxonomy

Pleurosternon bullocki fossils were first described by Richard Owen in 1841 from specimens found in the earliest Cretaceous (Berriasian) aged Purbeck Group of the Isle of Purbeck, of Dorset in southern England, under the living genus Platemys.[2] It was not until 1853 however, that it was published under the name Pleurosternon in a paper Owen presented to the Palaeontographical Society.[3] P. portlandicum named by Richard Lydekker in 1889 from the latest Jurassic (Tithonian) aged Portland Stone of the Isle of Portland, Dorset, is now considered a junior synonym of the P. bullocki.[4] In 2021 a second valid species, Pleurosternon moncayensis, was named from the Ágreda locality of Tarazona y el Moncayo, Aragon, Spain, which spans the Tithonian-Berriasian transition.[5]

Description

Skull of Pleurosternon bullocki
Skull of Pleurosternon bullocki

Pleurosternon has a very depressed carapace, much flatter than similar genera, such as the North American Late Jurassic and Early Cretaceous Glyptops.[6][7] Adults show little or none of the nuchal emargination that is more visible in juveniles.[7] The Xiphiplastras also have a large, V-shaped notch near the back of the bone.[7] The skull of P. bullocki is similar to that of other pleurosternids, and is similar in some aspects to those of pleurodires.[8] The known shell specimens of P. bullocki exhibit a large amount of variability, and also exhibit sexual dimorphism.[9]

Distribution and habitat

In Europe, P. bullocki is best known from southeast England's Purbeck Group and Portland stone, with over sixty carapaces known from the Purbeck Group alone.[9][10] Several areas within the formation became noted by some for producing Pleurosternon fossils. Among them were Swanage, Durlston Bay, Langton Matravers, and Herston.[7] P. bullocki is also known from disarticulated shell elements found in Tithonian aged deposits near Wimille in Pas-de-Calais in northern France.[4] As well as from numerous remains found in the Berriasian aged Angeac-Charente bonebed in western France, where it is the most abundant turtle.[11] The Purbeck Group, at the time was a coastal region with a complex system of shallow lagoons that slowly lost their salinity over time.[12] The Portland stone, however is a maritime deposit of slightly older age than the Purbeck, most bones found there are interpreted as having washed out to sea.

See also

References

  1. ^ E. Schweizerbart. 1994. Neues Jahrbuch für Geologie und Paläontologie: Monatshefte, Issues 7-12.
  2. ^ Owen, Richard. Report on British Fossil Reptilia. Report of the British Association for the Advancement of Science. P. p43- 126. 1841
  3. ^ Owen, R. A Monograph of the Fossil Chelonian Reptiles of the Wealden Clays and Purbeck Limestones. Palaeontographical Society, Vol. VII, 1853
  4. ^ a b Guerrero, A.; Pérez-García, A. (December 2020). "On the validity of the British Upper Jurassic turtle "Pleurosternon portlandicum" (Paracryptodira, Pleurosternidae)". Journal of Iberian Geology. 46 (4): 419–429. doi:10.1007/s41513-020-00136-x. ISSN 1698-6180. S2CID 225043638.
  5. ^ Pérez-García, A.; Martín-Jiménez, M.; Aurell, M.; Canudo, J.I.; Castanera, D. (2021-04-12). "A new Iberian pleurosternid (Jurassic-Cretaceous transition, Spain) and first neuroanatomical study of this clade of stem turtles". Historical Biology: 1–14. doi:10.1080/08912963.2021.1910818. ISSN 0891-2963. S2CID 234822940.
  6. ^ Boule, Marcellin. Priviteau, Jean. Les Fossiles. Éléments De Paléontologie. Libraries de L'académie Médecine. Paris, 1935. P. 433
  7. ^ a b c d Milner, Andrew R. (November 2004). "The turtles of the Purbeck Limestone Group of Dorset, southern England". Palaeontology. 47 (6): 1441–1467. doi:10.1111/j.0031-0239.2004.00418.x. ISSN 0031-0239.
  8. ^ Evers, Serjoscha W.; Rollot, Yann; Joyce, Walter G. (2020-06-30). "Cranial osteology of the Early Cretaceous turtle Pleurosternon bullockii (Paracryptodira: Pleurosternidae)". PeerJ. 8: e9454. doi:10.7717/peerj.9454. ISSN 2167-8359. PMC 7333654. PMID 32655997.
  9. ^ a b Guerrero, A.; Pérez-García, A. (2021-09-01). "Morphological variability and shell characterization of the European uppermost Jurassic to lowermost Cretaceous stem turtle Pleurosternon bullockii (Paracryptodira, Pleurosternidae)". Cretaceous Research. 125: 104872. doi:10.1016/j.cretres.2021.104872. ISSN 0195-6671.
  10. ^ Hay, Oliver Perry. 1908. Fossil Turtles of North America. Carnegie Institution of Washington. p. 45
  11. ^ Ronan Allain, Romain Vullo, Lee Rozada, Jérémy Anquetin, Renaud Bourgeais, et al.. Vertebrate paleobiodiversity of the Early Cretaceous (Berriasian) Angeac-Charente Lagerstätte (southwestern France): implications for continental faunal turnover at the J/K boundary. Geodiversitas, Museum National d’Histoire Naturelle Paris, In press. ffhal-03264773f
  12. ^ Radley, Jonathan D. Distribution and Environmental Significance of Molluscs in the Late Jurassic-Early Cretaceous Purbeck Formation of Dorset, Southern England: a Review. Life and Environments in Purbeck Times. (Special Papers in Palaeontology No. 68). p 48.