Pliosauroidea

Pliosauroidea is an extinct clade of marine reptiles. Pliosauroids, also commonly known as pliosaurs, are known from the Jurassic and Cretaceous periods. The pliosauroids were crocodile-like short-necked plesiosaurs with large heads and massive toothed jaws. They were sauropterygian swimming reptiles, and were not dinosaurs. They originally included only members of the family Pliosauridae, of the order Plesiosauria, but several other genera and families are now also included, the number and details of which vary according to the classification used.

Pliosauroids
Temporal range: Rhaetian - Cenomanian, 208–89.3 Ma
Cast of Rhomaleosaurus cramptoni, Natural History Museum, London
Liopleurodon ferox mounted skeleton, Museum of Paleontology, Tübingen
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: †Sauropterygia
Order: †Plesiosauria
Clade: †Neoplesiosauria
Suborder: †Pliosauroidea
Welles, 1943
Families and genera

see text

The distinguishing characteristics are a short neck and an elongated head, with larger hind flippers compared to the fore flippers, the opposite of the plesiosaurs. They were carnivorous and their long and powerful jaws carried many sharp, conical teeth. Pliosaurs range from 4 to 15 metres and more in length.[1][2] Their prey may have included fish, sharks, ichthyosaurs, dinosaurs and other plesiosaurs.

The largest known species are Kronosaurus and Pliosaurus macromerus; other well known genera include Rhomaleosaurus, Peloneustes, and Macroplata.[3] Fossil specimens have been found in Africa, Australia, China, Europe, North America and South America.

Many very early (from the Early Jurassic and possibly Latest Triassic, i.e. Rhaetian) primitive pliosauroids were very like plesiosauroids in appearance and, indeed, used to be included in the family Plesiosauridae.

Name
Liopleurodon ferox

Pliosauroidea was named by Welles in 1943. It is adapted from the name of the genus Pliosaurus, which is derived from the Greek πλειων (pleion), meaning "more/closely", and σαυρος (sauros) meaning "lizard"; it therefore means "more saurian". The name Pliosaurus was coined in 1841 by Richard Owen, who believed that it represented a link between plesiosauroids and crocodilians (considered a type of "saurian"), particularly due to their crocodile-like teeth.

Classification

Taxonomy
Macroplata
Kronosaurus
Liopleurodon
Simolestes vorax

The taxonomy presented here is mainly based on the plesiosaur cladistic analysis proposed by Hilary F. Ketchum and Roger B. J. Benson, 2011 unless otherwise noted.[4]

Phylogeny
Cast of "Plesiosaurus" macrocephalus found by Mary Anning, Muséum national d'histoire naturelle, Paris

Pliosauroidea is a stem-based taxon that was defined by Welles as "all taxa more closely related to Pliosaurus brachydeirus than to Plesiosaurus dolichodeirus". Pliosauridae and Rhomaleosauridae are stem-based taxa too. Pliosauridae is defined as "all taxa more closely related to Pliosaurus brachydeirus than to Leptocleidus superstes, Polycotylus latipinnis or Meyerasaurus victor". Rhomaleosauridae is defined as "all taxa more closely related to Meyerasaurus victor than to Leptocleidus superstes, Pliosaurus brachydeirus or Polycotylus latipinnis".[8] The cladogram below follows a 2011 analysis by paleontologists Hilary F. Ketchum and Roger B. J. Benson, and reduced to genera only.[4]

Pliosauroidea
Rhomaleosauridae
 

Anningasaura

 
 
 
 

"Plesiosaurus" macrocephalus

 
 
 

Archaeonectrus

 
 

Macroplata

 
 
 
 
 

Atychodracon

 
 
 

Eurycleidus

 
 
 

Rhomaleosaurus

 
 
 

Meyerasaurus

 
 

Maresaurus

 
 
 
 
 
 
 
Pliosauridae
 

Thalassiodracon

 
 
 

Hauffiosaurus

 
 
 

Attenborosaurus

 
 
 
 

BMNH R2439

 
 

Marmornectes

 
 
 
 

"Pliosaurus" andrewsi

 
 
 
 

OUMNH J.02247

 
 

Peloneustes

 
 
 
 

Simolestes

 
 
 

Liopleurodon

 
 
 

Pliosaurus

 
 
 

Megacephalosaurus[9]

 
 
 

Brachauchenius

 
 

Kronosaurus

 
 
 
 
 
 
 
 
 
 
 
 
 

Large pliosauroids

In 2002, the discovery of a very large pliosauroid was announced in Mexico. This pliosauroid came to be known as the "Monster of Aramberri". Although widely reported as such, it does not belong to the genus Liopleurodon.[10] The remains of this animal, consisting of a partial vertebral column, were dated to the Kimmeridgian of the La Caja Formation.[11] The fossils were found much earlier, in 1985, by a geology student and were at first erroneously attributed to a theropod dinosaur by Hahnel.[12] The remains originally contained part of a rostrum with teeth (now lost).

In August 2006, palaeontologists of the University of Oslo discovered the first remains of a pliosaur on Norwegian soil. The remains were described as "very well preserved, as well as being unique in their completeness". The large animal was determined to be a new species of Pliosaurus.[3] In the summer of 2008, the fossil remains of the huge pliosaur were dug up from the permafrost on Svalbard, a Norwegian island close to the North Pole.[13] The excavation of the find is documented in the 2009 History television special Predator X.

On 26 October 2009, palaeontologists reported the discovery of potentially the largest pliosauroid yet found. Found in cliffs near Weymouth, Dorset, on Britain's Jurassic coast, the fossil had a skull length of 6 feet 5 inches (2 meters). Palaeontologist Richard Forrest told the BBC: "I had heard rumours that something big was turning up. But seeing this thing in the flesh, so to speak, is just jaw dropping. It is simply enormous."[14] It was determined that the specimen belonged to a new species that scientists named Pliosaurus kevani.[15]

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References
  1. zoom dinosaurs
  2. Sea reptile is biggest on record. BBC News, February 27, 2008.
  3. Espen M. Knutsen, Patrick S. Druckenmiller and Jørn H. Hurum (2012). "A new species of Pliosaurus (Sauropterygia: Plesiosauria) from the Middle Volgian of central Spitsbergen, Norway". Norwegian Journal of Geology. 92 (2–3): 235–258. ISSN 0029-196X.CS1 maint: uses authors parameter (link) Low resolusion pdf Archived 2012-12-02 at the Wayback Machine High resolusion pdf
  4. 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.
  5. Sato, Tamaki; Xiao-Chun Wu (2008). "A new Jurassic pliosaur from Melville Island, Canadian Arctic Archipelago". Canadian Journal of Earth Sciences. 45 (3): 303–320. doi:10.1139/E08-003.
  6. Adam S. Smith and Gareth J. Dyke (2008). "The skull of the giant predatory pliosaur Rhomaleosaurus cramptoni: implications for plesiosaur phylogenetics" (PDF). Naturwissenschaften. 95 (10): 975–980. doi:10.1007/s00114-008-0402-z. PMID 18523747.
  7. Gasparini, Zulma (2009). "A New Oxfordian Pliosaurid (Plesiosauria, Pliosauridae) in the Caribbean Seaway" (PDF). Palaeontology. 52 (3): 661–669. doi:10.1111/j.1475-4983.2009.00871.x. Archived from the original (pdf) on 2011-07-16.
  8. Ketchum, H.F.; Benson, R.B.J. (2010). "Global interrelationships of Plesiosauria (Reptilia, Sauropterygia) and the pivotal role of taxon sampling in determining the outcome of phylogenetic analyses". Biological Reviews of the Cambridge Philosophical Society. 85 (2): 361–392. doi:10.1111/j.1469-185X.2009.00107.x. PMID 20002391.
  9. Schumacher, B. A.; Carpenter, K.; Everhart, M. J. (2013). "A new Cretaceous Pliosaurid (Reptilia, Plesiosauria) from the Carlile Shale (middle Turonian) of Russell County, Kansas". Journal of Vertebrate Paleontology. 33 (3): 613–628. doi:10.1080/02724634.2013.722576.
  10. "Archived copy". Archived from the original on 2011-07-15. Retrieved 2017-09-18.CS1 maint: archived copy as title (link)
  11. M.-C. Buchy, E. Frey, W. Stinnesbeck, J.-G. Lopez-Oliva (2003) "First occurrence of a gigantic pliosaurid plesiosaur in the late Jurassic (Kimmeridgian) of Mexico", Bull. Soc. geol. Fr., 174(3), pp. 271-278
  12. Hahnel W. (1988) "Hallazgo de restos de dinosaurio en Aramberri, N.L., Mexico", Actas Fac. Cienc. Tierra UANL Linares, 3, 245-250.
  13. Fox News: Predator X Was Most Fearsome Animal to Swim Oceans
  14. Morelle, Rebecca (27 October 2009). "Colossal 'sea monster' unearthed". BBC News.
  15. Benson, Roger J. B.; Evans, Mark; Smith, Adam S.; Sassoon, Judyth; Moore-Faye, Scott; Ketchum, Hilary F.; Forrest, Richard (2013-05-13). "A Giant Pliosaurid Skull from the Late Jurassic of England". PLOS One. 8: e65989. doi:10.1371/journal.pone.0065989. PMC 3669260. PMID 23741520.
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