Pleurosternon

Pleurosternon is an extinct genus of cryptodire turtle from the late Jurassic period to the early Cretaceous period.[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.

Pleurosternon
Temporal range: 161.2–99.6 Ma
Late Jurassic-Early Cretaceous
Pleurosternon
Pleurosternon (ovatum) bullocki fossil
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Testudines
Suborder: Cryptodira
Family: Pleurosternidae
Genus: Pleurosternon
Owen, 1853
Species
  • P. bullocki (Owen, 1842) Type
  • P. portlandicum (Lydekker, 1889)

Taxonomy

Pleurosternon fossils were first described by Richard Owen in 1841 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]

Phylogeny

Cladogram after Tyler R. Lyson and Walter G. Joyce (2009).[4]

Pleurosternon bullocki

Glyptops plicatulus

 Baenidae 
 Neurankylinae 

Neurankylus eximius

Trinitichelys hiatti

 Eubaeninae 

Hayemys latifrons

 Baenodda
 Plesiobaenini

Plesiobaena antiqua

Peckemys brinkman

Cedrobaena putorius

Gamerabaena sonsalla

Palatobaena cohen

Palatobaena bairdi

Palatobaena gaffneyi

 Eubaenini

Boremys pulchra

Boremys grandis

Eubaena cephalica

Goleremys mckennai

Stygiochelys estesi

Baena arenosa

Chisternon undatum

Description

Pleurosternon ovatum
Carapace fossil of P. bullocki, side view.

Pleurosternon has a very depressed carapace, much flatter than similar genera, such as the North American Late Jurassic and Early Cretaceous Glyptops.[5][6] Adults show little or none of the nuchal emargination that is more visible in juveniles.[6] The Xiphiplastras also have a large, V-shaped notch near the back of the bone.[6] Together with Platychelys, it is one of the few turtle genera to exhibit the characteristics of both modern turtle suborders, the Cryptodira and the Pleurodira.[7]

Distribution and habitat

In Europe, most species of Pleurosternon are best known from southeast England's Purbeck Group and Portland stone, some specimens were even recovered in the Purbeck's type locality.[8][9] Several areas within the formation became noted by some for producing pleurosternon fossils. Among them were Swanage, Durlston Bay, Langton Matravers, and Herston.[10]

The genus has also been found in several rock formations from the upper Jurassic in both France and Spain,[11] and from the Cretaceous Wealden group of both England and northern Germany.[12] The Purbeck formation, at the time was a coastal region with a complex system of shallow lagoons that slowly lost their salinity over time.[13] Similarly, the younger Wealden group was also coastal plain dominated by lagoons but with the addition of braided streams.[14] The Portland stone, however is a maritime deposit of similar age near the Purbeck, most bones found there are interpreted as having washed out to sea from the Wealden or the Purbeck. Because of this, Pleurosternon has been described as a "shore-turtle".[5]

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. ^ Tyler R. Lyson & Walter G. Joyce (2009). "A Revision of Plesiobaena (Testudines: Baenidae) and an Assessment of Baenid Ecology Across the K/T Boundary". Journal of Paleontology. 83 (6): 833–853. doi:10.1666/09-035.1.
  5. ^ a b Boule, Marcellin. Priviteau, Jean. Les Fossiles. Éléments De Paléontologie. Libraries de L'académie Médecine. Paris, 1935. P. 433
  6. ^ a b c Milner, Andrew R. 2004. The Turtles of the Purbeck Limestone of Dorset, Southern England. Palaeontology. Vol. 47. part 6. pp. 1446-1447
  7. ^ Neaverson, E. 1955. Stratigraphical Palaeontology: a Study of Ancient Life-Provences. Second Edition. Oxford. Clarendon Press. p.114
  8. ^ Hay, Oliver Perry. 1908. Fossil Turtles of North America. Carnegie Institution of Washington. p. 45
  9. ^ Neaverson, 466
  10. ^ Milner, 1448
  11. ^ A. PÉREZ GARCÍA, F ORTEGA & F ESCASO. A small pleurosternid turtle from the Upper Jurassic of Santa Rita (Torres Vedras, Portugal): Juvenile or new form? 7th Annual EAVP Meeting 2009. 56
  12. ^ Abel, Othenio. 1919. Die Stämme der Wirbeltlere. Verinigung Wissenschaftlicher Verleger. Berlin und Leipzig. p.412
  13. ^ 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.
  14. ^ Jackson, A.A.; 2008: Bedrock geology UK south. An explanation of the bedrock geology map of England and Wales - 1:625,000 edition, Keyworth, Nottingham, British Geological Survey, ISBN 978-0-85272-586-3.

External links

2012 in paleontology

Paleontology or palaeontology (from Greek: paleo, "ancient"; ontos, "being"; and logos, "knowledge") is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 2012.

Note: In 2012 International Code of Zoological Nomenclature was amended, with new regulations allowing the publication of new names and nomenclatural acts in zoology after 2011 in works "produced in an edition containing simultaneously obtainable copies by a method that assures (...) widely accessible electronic copies with fixed content and layout", provided that the work is registered in ZooBank before it is published, the work itself states the date of publication with evidence that registration has occurred, and the ZooBank registration states both the name of an electronic archive intended to preserve the work and the ISSN or ISBN associated with the work. New scientific names appearing in electronic works are not required to be registered in ZooBank, only the works themselves are. Works containing descriptions of some of the taxa listed below weren't printed on paper in 2012; however, the taxa that were described in works which were registered in ZooBank in 2012 are listed as valid.

Dorsetochelys

Dorsetochelys is an extinct genus of turtle from the Early Cretaceous of southern England and northwestern Germany.

Gamerabaena

Gamerabaena is an extinct genus of baenid turtle which existed in North Dakota during the late Cretaceous period. It is known from a single fragmentary skull that was found in the Maastrichtian-age Hell Creek Formation. It contains the species Gamerabaena sonsalla. Gamerabaena is similar to the genus Palatobaena, but it differs in its lack of a posterior expansion of the triturating (or chewing) surface, a somewhat rectangular skull, and a wide angle between the maxillae. Gamerabaena also has a lingual ridge on the inner side of the jaw that is not seen in Palatobaena.Gamerabaena is considered the sister taxon of Palatobaena and shares features with both Palatobaena and Plesiobaena. These features, which include slightly upturned eye sockets, are seen as intermediate between the two other genera. While Gamerabaena is known only from the skull, it may belong to the same species as "Baena" hayi, which is known primarily from the shell.The genus is named after Gamera, a giant flying, fire-breathing turtle from a series of Japanese tokusatsu films.

Lulworth Formation

The Lulworth Formation is a geologic formation in England. It dates from the late Tithonian to the mid Berriasian. It is a subunit of the Purbeck Group. It consists of three members, which are in ascending order, the Mupe Member, the Ridgway Member, and the Warbarrow Tout Member. The Mupe Member is typically 11 to 16 m thick and largely consists of marls and micrites with interbeds of calcareous mudstone. The Ridgeway Member is about 3 to 7 m thick and consists of in its western portion carbonaceous muds, marls and micrites, in the east the muds are replaced by micritic limestone. The Warbarrow Tout Member is 17 to 39 m thick and consists of limestone at the base and micrite and mudstone for the rest of the sequence, this member is the primary source of the vertebrate fossils within the formation.

Pleurosternidae

Pleurosternidae is an extinct family of turtles.

Polysternon

Polysternon is a genus of turtles in the extinct family Bothremydidae. It was described by Portis in 1882, and contains the species P. provinciale (originally placed in the genus Pleurosternon), which existed during the Cretaceous of what is now France; P. atlanticum, which existed during the Cretaceous at Laño in what is now Spain, and a new species, P. isonae, from the Late Maastrichtian of Spain.

The species epithet of P. isonae refers to the municipality Isona i Conca Dellà in Catalonia, where the type specimen was discovered in the Tremp Formation.

Prehistoric reptile

The term prehistoric reptile covers a broad category that is intended to help distinguish the dinosaurs from other prehistoric reptiles. As the dinosaurs, because of their long and successful reign for many millions of years, are almost exclusively dealt with in their own category of prehistoric life.

The category covers all the non-dinosaurian reptiles which are often erroneously considered to be dinosaurs, such as the seafaring varieties of plesiosaurs and the flying pterosaurs. Also included are ancient crocodiles such as Deinosuchus.

For information on the synapsids, which were previously known as "mammal-like reptiles" (including the well-known Dimetrodon), which are not part of the clade Sauropsida (with which "Reptilia" is generally synonymized), see Synapsid (amniotes related to mammals). For information on the ancestors of reptiles, traditionally classified as labyrinthodont amphibians, see Reptiliomorpha (reptile-like tetrapods).

Wessex Formation

The Wessex Formation is a fossil-rich English geological formation that dates from the Berriasian to Barremian stages (about 145–125 million years ago) of the Early Cretaceous. It forms part of the Wealden Group and underlies the younger Vectis Formation and overlies the Durlston Formation. The dominant lithology of this unit is mudstone with some interbedded sandstones.

Extinct turtles
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