Plesiosauroidea

Plesiosauroidea (/ˈpliːsiəsɔːr/; Greek: plēsios/πλησιος 'near' or 'close to' and sauros/σαυρος 'lizard') is an extinct clade of carnivorous plesiosaur marine reptiles. They have the snake-like longest neck to body ratio of any reptile. Plesiosauroids are known from the Jurassic and Cretaceous periods. After their discovery, some plesiosauroids were said to have resembled "a snake threaded through the shell of a turtle",[1] although they had no shell.

Plesiosauroidea appeared at the Early Jurassic Period (late Sinemurian stage) and thrived until the K-Pg extinction, at the end of the Cretaceous Period. The oldest confirmed plesiosauroid is Plesiosaurus itself, as all younger taxa were recently found to be pliosauroids.[2] While they were Mesozoic diapsid reptiles that lived at the same time as dinosaurs, they did not belong to the latter. Gastroliths are frequently found associated with plesiosaurs.[3]

Plesiosauroidea
Temporal range: Late Triassic - Late Cretaceous, 210–66 Ma
Thalassomedon
Reconstructed skeleton of Thalassomedon hanningtoni, an elasmosaurid
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: Sauropterygia
Order: Plesiosauria
Clade: Neoplesiosauria
Superfamily: Plesiosauroidea
Gray, 1825
Families

See text

History of discovery

Mary Anning Plesiosaurus
Autograph letter concerning the discovery of Plesiosaurus, from Mary Anning.

The first complete plesiosauroid skeletons were found in England by Mary Anning, in the early 19th century, and were amongst the first fossil vertebrates to be described by science. Plesiosauroid remains were found by the Scottish geologist Hugh Miller in 1844 in the rocks of the Great Estuarine Group (then known as 'Series') of western Scotland.[4] Many others have been found, some of them virtually complete, and new discoveries are made frequently. One of the finest specimens was found in 2002 on the coast of Somerset (England) by someone fishing from the shore. This specimen, called the Collard specimen after its finder, was on display in Taunton Museum in 2007. Another, less complete, skeleton was also found in 2002, in the cliffs at Filey, Yorkshire, England, by an amateur palaeontologist. The preserved skeleton is displayed at Rotunda Museum in Scarborough.

Description

Dolichorhynchops
Dolichorhynchops, a short-necked, long-jawed plesiosauroid, National Museum of Natural History, Washington D.C., USA.

Plesiosauroids had a broad body and a short tail. They retained their ancestral two pairs of limbs, which evolved into large flippers.

It has been determined by teeth records that several sea-dwelling reptiles, including plesiosauroids, had a warm-blooded metabolism similar to that of mammals. They could generate endothermic heat to survive in colder habitats.[5]

Evolution

Plesiosauroids evolved from earlier, similar forms such as pistosaurs. There are a number of families of plesiosauroids, which retain the same general appearance and are distinguished by various specific details. These include the Plesiosauridae, unspecialized types which are limited to the Early Jurassic period; Cryptoclididae, (e.g. Cryptoclidus), with a medium-long neck and somewhat stocky build; Elasmosauridae, with very long, flexible necks and tiny heads; and the Cimoliasauridae, a poorly known group of small Cretaceous forms. According to traditional classifications, all plesiosauroids have a small head and long neck but, in recent classifications, one short-necked and large-headed Cretaceous group, the Polycotylidae, are included under the Plesiosauroidea, rather than under the traditional Pliosauroidea. Size of different plesiosaurs varied significantly, with an estimated length of Trinacromerum being three meters and Mauisaurus growing to twenty meters.

Relationships

Muraenosaurus BW
Muraenosaurus, a cryptoclidid
Styxosaurus BW
Styxosaurus, an elasmosaurid
Dolichorhynchops BW
Dolichorhynchops, a polycotylid

The following cladogram follows an analysis by Benson & Druckenmiller (2014).[6]

Plesiosauroidea

Plesiosaurus

Eretmosaurus

Westphaliasaurus

Microcleididae

Plesiopterys

Cryptoclidia

Cryptoclididae

Xenopsaria

Elasmosauridae

Leptocleidia

Leptocleididae

Polycotylidae

Behavior

Plesiosaurus 3DB
Restoration of a Plesiosaurus dolichodeirus pair, one catching a fish.

Unlike their pliosauroid cousins, plesiosauroids (with the exception of the Polycotylidae) were probably slow swimmers.[7] It is likely that they cruised slowly below the surface of the water, using their long flexible neck to move their head into position to snap up unwary fish or cephalopods. Their four-flippered swimming adaptation may have given them exceptional maneuverability, so that they could swiftly rotate their bodies as an aid to catching prey.

Contrary to many reconstructions of plesiosauroids, it would have been impossible for them to lift their head and long neck above the surface, in the "swan-like" pose that is often shown {Everhart, 2005}.[8] Even if they had been able to bend their necks upward to that degree (which they could not), gravity would have tipped their body forward and kept most of the heavy neck in the water.

On 12 August 2011, researchers from the U.S. described a fossil of a pregnant plesiosaur found on a Kansas ranch in 1987.[9] The plesiosauroid, Polycotylus latippinus, has confirmed that these predatory marine reptiles gave birth to single, large, live offspring - contrary to other marine reptile reproduction which typically involves a large number of small babies. Before this study, plesiosauroids had sometimes been portrayed crawling out of water to lay eggs in the manner of sea turtles, but experts had long suspected that their anatomy was not compatible with movement on land. The adult plesiosaur measures 4 m long and the juvenile is 1.5 m long.[10]

References

  1. ^ Everhart, Mike (2005-10-14). "A Snake Drawn Through the Shell of a Turtle". Oceans of Kansas Paleontology. Retrieved 2010-06-10 External link in |work= (help)
  2. ^ Hilary F. Ketchum and Roger B. J. Benson (2011). "A new pliosaurid (Sauropterygia, Plesiosauria) from the Oxford Clay Formation (Middle Jurassic, Callovian) of England: evidence for a gracile, longirostrine grade of Early-Middle Jurassic pliosaurids". Special Papers in Palaeontology. 86: 109–129. doi:10.1111/j.1475-4983.2011.01083.x (inactive 2019-06-30).CS1 maint: Uses authors parameter (link)
  3. ^ "Occurrence of Gastroliths in Mesozoic Taxa," in Sanders et al. (2001). Page 168.
  4. ^ p 339 Trewin, N. H. (ed)2002 The Geology of Scotland. The Geological Society, London
  5. ^ Bernard, A.; Lecuyer, C.; Vincent, P.; Amiot, R.; Bardet, N.; Buffetaut, E.; Cuny, G.; Fourel, F.; Martineau, F.; Mazin, J.-M.; Prieur, A. (2010-06-15). "Warm-blooded marine reptiles at the time of the dinosaurs". Science. Sciencedaily.com. 328 (5984): 1379–1382. Bibcode:2010Sci...328.1379B. doi:10.1126/science.1187443. PMID 20538946. Retrieved 2011-08-15.
  6. ^ Benson, R. B. J.; Druckenmiller, P. S. (2013). "Faunal turnover of marine tetrapods during the Jurassic-Cretaceous transition". Biological Reviews. 89 (1): 1–23. doi:10.1111/brv.12038. PMID 23581455.
  7. ^ Massare, J. A. (1988). "Swimming capabilities of Mesozoic marine reptiles: Implications for method of predation". Paleobiology. 14 (2): 187–205. doi:10.1017/s009483730001191x.
  8. ^ Henderson, D. M. (2006). "Floating point: a computational study of buoyancy, equilibrium, and gastroliths in plesiosaurs". Lethaia. 39 (3): 227–244. doi:10.1080/00241160600799846.
  9. ^ F. R. O’Keefe1,*, L. M. Chiappe2. "Viviparity and K-Selected Life History in a Mesozoic Marine Plesiosaur (Reptilia, Sauropterygia)". Sciencemag.org. Retrieved 2011-08-15.CS1 maint: Multiple names: authors list (link)
  10. ^ by Anthony King. "Ancient sea dragons had a caring side". Cosmosmagazine.com. Archived from the original on 2011-10-01. Retrieved 2011-08-15.

Sources

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External links

Anningasaura

Anningasaura is an extinct genus of basal plesiosaur. It is known from a single type species, A. lymense, discovered in Early Jurassic rocks of Lyme Regis in the United Kingdom.

Attenborosaurus

Attenborosaurus is an extinct genus of pliosaurid from the Early Jurassic of Dorset, England. The type species is A. conybeari. The genus is named after David Attenborough, the species after William Conybeare.

Cryptoclidia

Cryptoclidia is a clade of plesiosaurs.

Cryptoclidia was named and defined as a node clade in 2010 by Hilary Ketchum and Roger Benson: the group consisting of the last common ancestor of Cryptoclidus eurymerus and Polycotylus latipinnis; and all its descendants.The following cladogram follows an analysis by Benson & Druckenmiller (2014).

Edgarosaurus

Edgarosaurus is a genus of polycotylid plesiosaur, containing one species, E. muddi. The type specimen was found in Early Cretaceous (late Albian) rocks in the state of Montana in the United States. At the time, this location was covered by part of the Western Interior Seaway.

Eoplesiosaurus

Eoplesiosaurus is an extinct genus of basal plesiosauroid known from the Early Jurassic period (most likely earliest Hettangian stage) of the United Kingdom. It contains a single species, E. antiquior.

Kimmerosaurus

Kimmerosaurus ("lizard from Kimmeridge") is an extinct genus of plesiosaur from the family Cryptoclididae, closely related to Tatenectes.

Leptocleidia

Leptocleidia is a clade of plesiosauroids. The group was erected in 2007 as Leptocleidoidea. Although established as a clade, the name Leptocleidoidea implies that it is a superfamily. Leptocleidoidea is placed within the superfamily Plesiosauroidea, so it was renamed Leptocleidia by Hilary F. Ketchum and Roger B. J. Benson (2010) to avoid confusion with ranks. Leptocleidia is a node-based taxon which was defined by Ketchum and Benson as "Leptocleidus superstes, Polycotylus latipinnis, their most recent common ancestor and all of its descendants".

Leurospondylus

Leurospondylus is a genus of plesiosaur whose family is currently disputed, but is suggested to be Plesiosauridae.

Meyerasaurus

Meyerasaurus is an extinct genus of rhomaleosaurid known from Holzmaden, Baden-Württemberg of southwestern Germany.

Microcleididae

Microcleididae is an extinct family of basal plesiosauroid plesiosaurs from the Early Jurassic (middle Sinemurian to late Toarcian stages) of France, Germany, Portugal and the United Kingdom. Currently, the oldest and the most known microcleidid is Eretmosaurus from the middle Sinemurian of the United Kingdom. Microcleididae was formally named and described by Roger B. J. Benson, Mark Evans and Patrick S. Druckenmiller in 2012.

Microcleidus

Microcleidus is an extinct genus of sauropterygian reptile belonging to the Plesiosauroidea. It was about the size of a medium-sized dolphin, reaching a length of 3 metres (9.8 ft). The species has 40 neck vertebrae and a short tail of 28 vertebrae.

Plesiosauria

The Plesiosauria (; Greek: πλησίος, plesios, meaning "near to" and sauros, meaning "lizard") or plesiosaurs are an order or clade of extinct Mesozoic marine reptiles (marine Sauropsida), belonging to the Sauropterygia.

Plesiosaurs first appeared in the latest Triassic Period, possibly in the Rhaetian stage, about 203 million years ago. They became especially common during the Jurassic Period, thriving until their disappearance due to the Cretaceous–Paleogene extinction event at the end of the Cretaceous Period, about 66 million years ago. They had a worldwide oceanic distribution.

Plesiosaurs were among the first fossil reptiles discovered. In the beginning of the nineteenth century, scientists realised how distinctive their build was and they were named as a separate order in 1835. The first plesiosaurian genus, the eponymous Plesiosaurus, was named in 1821. Since then, more than a hundred valid species have been described. In the early twenty-first century, the number of discoveries has increased, leading to an improved understanding of their anatomy, relationships and way of life.

Plesiosaurs had a broad flat body and a short tail. Their limbs had evolved into four long flippers, which were powered by strong muscles attached to wide bony plates formed by the shoulder girdle and the pelvis. The flippers made a flying movement through the water. Plesiosaurs breathed air, and bore live young; there are indications that they were warm-blooded.

Plesiosaurs showed two main morphological types. Some species, with the "plesiosauromorph" build, had (sometimes extremely) long necks and small heads; these were relatively slow and caught small sea animals. Other species, some of them reaching a length of up to seventeen metres, had the "pliosauromorph" build with a short neck and a large head; these were apex predators, fast hunters of large prey. The two types are related to the traditional strict division of the Plesiosauria into two suborders, the long-necked Plesiosauroidea and the short-neck Pliosauroidea. Modern research, however, indicates that several "long-necked" groups might have had some short-necked members or vice versa. Therefore, the purely descriptive terms "plesiosauromorph" and "pliosauromorph" have been introduced, which do not imply a direct relationship. "Plesiosauroidea" and "Pliosauroidea" today have a more limited meaning. The term "plesiosaur" is properly used to refer to the Plesiosauria as a whole, but informally it is sometimes meant to indicate only the long-necked forms, the old Plesiosauroidea.

Plesiosauridae

The Plesiosauridae are a monophyletic group of plesiosaurs.A family Plesiosauridae was first named by John Edward Gray in 1825.

Pliosauridae

Pliosauridae is a family of plesiosaurian marine reptiles from the Earliest Jurassic to the early Late Cretaceous (Hettangian to Turonian stages) of Australia, Europe, North America and South America. Past the Turonian, they may have been replaced by the mosasaurs. It was formally named by Harry G. Seeley in 1874.

Polycotylidae

Polycotylidae is a family of plesiosaurs from the Cretaceous, a sister group to Leptocleididae.

With their short necks and large elongated heads, they resemble the pliosaurs, but closer phylogenetic studies indicate that they share many common features with the Plesiosauridae and Elasmosauridae. They have been found worldwide, with specimens reported from New Zealand, Australia, Japan, Morocco, the US, Canada, Eastern Europe, and South America.

Rhomaleosauridae

Rhomaleosauridae is a family of pliosauroid plesiosaurs from the Earliest Jurassic to the latest Middle Jurassic (Hettangian to Callovian stages) of Europe, North America, South America and possibly Asia. Most rhomaleosaurids are known from England, many specifically from lower Blue Lias deposits that date back to the earliest Jurassic, just at the boundary with the Triassic. In fact, to date only two undisputed rhomaleosaurids were named from outside Europe - the closely related Borealonectes russelli and Maresaurus coccai from Canada and Argentina, respectively. These two species are also the only Middle Jurassic representatives of the family. Rhomaleosauridae was formally named by Kuhn in 1961, originally proposed to include Rhomaleosaurus cramptoni and its relatives, which have short necks and large heads relatively to plesiosauroids like Elasmosaurus and Plesiosaurus, but longer necks and smaller heads relatively to advanced pliosaurids like Pliosaurus and Kronosaurus.

Seeleyosaurus

Seeleyosaurus is an extinct genus of plesiosaur. It is known from a large almost complete skeleton from the Upper Lias (Toarcian) of Württemberg, Germany. There seems to be the impression of a rhomboidal flap of skin in a vertical plane; if so, many plesiosaurs may have been equipped in this way.

Trinacromerum

Trinacromerum is an extinct genus of sauropterygian reptile, a member of the polycotylid plesiosaurs. It contains two species, T. bentonianum and T. kirki. Specimens have been discovered in the Late Cretaceous fossil deposits of what is now modern Kansas and Manitoba.

Umoonasaurus

Umoonasaurus is an extinct genus of plesiosaur belonging to the family Leptocleididae. This genus lived approximately 115 million years ago (Aptian-Albian) in shallow seas covering parts of what is now Australia. It was a relatively small animal around 2.5 m (8 ft) long. An identifying trait of Umoonasaurus is three crest-ridges on its skull.

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