Plesiosaurus
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The holotype skeleton of Plesiosaurus . |
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| Lower Jurassic (Hettangian to Sinemurian) | ||||||||||
| 201.3 to 190.8 million years | ||||||||||
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| Scientific name | ||||||||||
| Plesiosaurus | ||||||||||
| De la Bèche & Conybeare , 1821 | ||||||||||
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Plesiosaurus is an extinct genus of long-necked marine reptiles fromthe Plesiosauria clade of the same name. Discovered by fossil collector and paleontologist Mary Anning in the early 19th century near Lyme Regis ,Britain, Plesiosaurus is one of the first extinct marine reptiles to be scientifically described. As the " archetype " of a plesiosaur,hundreds of species from different parts of the Mesozoic Era have been assigned tothe genus Plesiosaurus since it was first described. According to the current status, however, the genus is limited to the species Plesiosaurus dolichodeirus from the Lower Jurassic of Great Britain discovered by Anning.
description
As with all other Plesiosauria, the body of Plesiosaurus was adapted to a life in the sea, so the genus, like many other marine reptiles and marine mammals, had limbs converted into paddles, with the front paddles in Plesiosaurus being slightly longer than the rear paddles . For most Plesiosauroids, the neck of Plesiosaurus was also very elongated and consisted of 40 cervical vertebrae in Plesiosaurus . At the end of it sat a relatively small skull with a set of pointed teeth .
The features that distinguish Plesiosaurus from other known Plesiosauria include a relatively short skull with a wide, but nevertheless pointed snout, almost circular temple windows , and features of the thoracic and pelvic girdle .
Plesiosaurus was a relatively small genus of plesiosaurs that reached a length of about 3.5 meters.
Research history
The genus Plesiosaurus was first mentioned in a treatise by the British geologists Henry Thomas de la Bèche and William Daniel Conybeare in 1821 on fossil finds from the Jurassic Blue Lias . In it, they describe, among other things, eddies and paddle remains of a hitherto unknown marine reptile, which, according to de la Bèche and Conybeare, has more similarities with a crocodile than the then already known Ichthyosaurus from the same layers . As a result, they name it the new genus Plesiosaurus , but without introducing a suitable biological species.
The formal naming of the type species Plesiosaurus dolichodeirus was not given until 1824 by Conybeare based on a skeleton from the Sinemurium near Lyme Regis found and sketched by the British collector and paleontologist Mary Anning in December 1823 . Conybeare describes the long neck and paddle of Plesiosaurus for the first time and makes a first reconstruction of the skeleton. Conybeare interprets the locomotion of Plesiosaurus as similar to today's sea turtles , with the animals staying near the surface of the water and searching for food with their necks like a swan underwater (a function of the neck that is no longer supported today).
Conybeare also reports in his work about another Plesiosaurus species that had a significantly shorter neck than P. dolichodeirus and is called Plesiosaurus giganteus by Conybeare (actually a Pliosaurid ). Since the material originally described by de la Bèche and Conybeare as Plesiosaurus comes from different sites and has not been adequately described, Anning's skeleton was used by the following authors as a type for both the species P. dolichodeirus and the genus Plesiosaurus . A species named Plesiosaurus priscus, established by James Parkinson on the basis of material from de la Bèche and Conybeare as early as 1822, is only a nomen dubium . Mary Anning and her work are completely unmentioned in Conybeares work.
In the course of the following 170 years, hundreds of other species were assigned to Plesiosaurus . This came partly as P . dolichodeirus from the Lyme Regis, but also from other parts of the world and extended over a period from the Upper Triassic to the end of the Cretaceous . From the Lyme Regis, the anatomist Richard Owen described the species Plesiosaurus macromorus based on remnants of the limbs and the spine also found by Anning .
The first to take a detailed look at the taxonomy of the original genus was the paleontologist Glenn W. Storrs in 2003. Storrs showed that Owens P. macromorus is merely a synonym for P. dolichodeirus . Furthermore, Storrs was able to show that the genus Plesiosaurus is limited to the type species P. dolichodeirus , while the numerous other species cannot be assigned to the genus. According to Storrs, the only exception are the remains of Plesiosaurus guilelmiimperatoris from the Toarcium of Baden-Württemberg . This is now also placed in its own genus called Seeleyosaurus .
Systematics
As one of the earliest members of the Plesiosauria , Plesiosaurus stands near the base of the Plesiosauroidea group . Occasionally, Plesiosaurus is placed in a separate family called Plesiosauridae with other early representatives such as Seeleyosaurus and Hydrorion .
Abbreviated cladogram of the Plesiosauroidea according to Ketchum & Benson (2010).
| Plesiosauroidea |
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Abbreviated cladogram of the Plesiosauroidea according to Benson & Druckermiller (2013).
| Plesiosauroidea |
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Paleoecology
The layers in which Plesiosaurus dolichodeirus was found were deposited in a shallow sea , not particularly far from the coast. Plesiosaurus shared this habitat with many other marine reptiles, including the pliosaurids Archaeonectrus and several genera of ichthyosaurs such as Ichthyosaurus , Leptonectes and Temnodontosaurus .
In addition to other typical marine animals such as mussels and ammonites, there are also remains of land organisms such as insects and various plants . Fossils of land reptiles such as the pterosaur Dimorphodon and the dinosaur Scelidosaurus are also known from the layers of Lyme Regis.
literature
- Conybeare, WD (1824). XXI. — On the discovery of an almost perfect skeleton of the Plesiosaurus . Transactions of the Geological Society of London , 2 (2), 381-389.
- De la Bèche, HT, & Conybeare, WD (1821). XXX. — Notice of the discovery of a new Fossil Animal, forming a link between the Ichthyosaurus and Crocodile, together with general remarks on the Osteology of the Ichthyosaurus . Transactions of the Geological Society of London , 1 (1), 559-594.
- Storrs, GW (1997). Morphological and taxonomic clarification of the genus Plesiosaurus . In Ancient Marine Reptiles (pp. 145–190). Academic Press. doi: 10.1016 / B978-012155210-7 / 50010-7
Individual evidence
- ↑ https://paleobiodb.org/classic/basicTaxonInfo?taxon_no=100059
- ^ Zammit, M., Daniels, CB, & Kear, BP (2008). Elasmosaur (Reptilia: Sauropterygia) neck flexibility: Implications for feeding strategies. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology , 150 (2), 124-130.
- ^ Noè, LF, Taylor, MA, & Gómez-Pérez, M. (2017). An integrated approach to understanding the role of the long neck in plesiosaurs. Acta Palaeontologica Polonica , 62 (1), 137-162.
- ↑ Knutsen, EM (2012). A taxonomic revision of the genus Pliosaurus (Owen, 1841a) Owen, 1841b. Norwegian Journal of Geology , 92, 259-276.
- ↑ Großmann, F. (2007). The taxonomic and phylogenetic position of the Plesiosauroidea from the Lower Jurassic Posidonia Shale of South-West Germany. Palaeontology , 50 (3), 545-564. doi: 10.1111 / j.1475-4983.2007.00654.x
- ^ Ketchum, HF & Benson, RBJ (2010). Global interrelationships of Plesiosauria (Reptilia, Sauropterygia) and the pivotal role of taxon sampling in determining the outcome of phylogenetic analyzes. Biological Reviews , 85 (2), 361-392. doi: 10.1111 / j.1469-185X.2009.00107.x
- ^ Benson, RBJ & Druckermiller, PS (2013). Faunal turnover of marine tetrapods during the Jurassic-Cretaceous transition. Biological Reviews , 89 (1), 1-23. doi: 10.1111 / brv.12038
- ^ Benton, MJ & Spencer, PS (1995). British Early Jurassic fossil reptile sites. In: Fossil Reptiles of Great Britain , 97–121. doi: 10.1007 / 978-94-011-0519-4_5