Liopleurodon

Liopleurodon Temporal range: Middle–Late Jurassic, 162–150Ma PreЄ Є O S D C P T J K Pg N
L. ferox skeleton
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	†Plesiosauria
Suborder:	†Pliosauroidea
Family:	†Pliosauridae
Genus:	†Liopleurodon Sauvage, 1873
Species
L. ferox Sauvage, 1873 (type) L. pachydeirus (Seeley, 1869)
Synonyms
Pliosaurus ferox

Liopleurodon (/ˌlaɪ.ɵˈplʊərədɒn/; meaning 'smooth-sided teeth') is a genus of large, carnivorous marine reptile belonging to the Pliosauroidea, a clade of short-necked plesiosaurs. The two species of Liopleurodon lived during the Callovian stage of the Middle Jurassic Period (c. 160 to 155 mya). It was the apex predator of the Middle to Late Jurassic seas that covered Europe. The largest species, L. ferox, is estimated to have grown up to 6.39 metres (21.0 ft) in length.^[1]

The name "Liopleurodon" (meaning "smooth-sided tooth") derives from Greek words: λεῖος [leios], "smooth"; pleurá, side or rib; and odṓn, tooth.

Discovery and species

L. ferox skull

The genus name Liopleurodon was coined by Henri Émile Sauvage in 1873 on the basis of very poor remains consisting of three 70 millimeter (2¾ inch) teeth. One tooth, found near Boulogne-sur-Mer, France in layers dating from the Callovian, was named Liopleurodon ferox, another from Charly, France was named Liopleurodon grossouvrei, while a third discovered near Caen, France was originally described as Poikilopleuron bucklandi and ascribed by Sauvage to the species Liopleurodon bucklandi. Sauvage did not ascribe the genus to any particular group of reptiles in his descriptions.^[2]

Liopleurodon fossils have been found mainly in England and France, with one younger species known from Russia. Fossil specimens that are contemporary (Callovian) with those from England and France referrable to Liopleurodon are known from Germany.^[3]

Currently, there are two recognized species within Liopleurodon. From the Callovian of England and France L. ferox is well known; while also from the Callovian of England is the rarer L. pachydeirus, described by Seeley as a Pliosaurus (1869).^[4] Only L. ferox is known from more or less complete skeletons.

Palaeobiology

Four strong paddle-like limbs suggest that Liopleurodon was a powerful swimmer. Its four-flipper mode of propulsion is characteristic of all plesiosaurs. A study involving a swimming robot has demonstrated that although this form of propulsion is not especially efficient, it provides very good acceleration - a desirable trait in an ambush predator.^[5][6] Studies of the skull have shown that it could probably scan the water with its nostrils to ascertain the source of certain smells.^[7]

Size

Estimating the maximum size of Liopleurodon has become a controversial subject. The palaeontologist L. B. Tarlo suggested that the total body length of a pliosaur (including Liopleurodon) can be estimated from its skull length. Tarlo claimed that the skull of a pliosaur is typically about one-seventh of the total body length. The largest known skull belonging to L. ferox is 1.54 metres (5.1 ft) long.^[8] According to Tarlo's hypothesis, this specimen would be around 10.5 metres (34 ft) long. However, the case of Kronosaurus exposed some uncertainty about the accuracy of Tarlo's suggestion.^[9]

Liopleurodon ferox

New research on pliosaur anatomy has cast doubt on Tarlo's hypothesis for estimating the size of pliosaurs and revealed that pliosaur skulls were typically about one-fifth of the total body length. An exceptionally well-preserved skeleton of L. ferox is on display in the Institut und Museum für Geologie und Paläontologie der Universität Tübingen in Germany. This specimen is around 4.5 metres (15 ft) long.^[10] Fossil remains of another specimen identified as L. ferox have been excavated from an Oxford Clay formation near Peterborough. This specimen has been estimated to be 6.39 metres (21.0 ft) in length with a skull length of about 1.26 metres (4.1 ft) and is regarded as an adult individual.^[1] An adult L. ferox would have averaged 5–7 metres (16–23 ft) long.^[9]

Some fossil remains excavated from the Kimmeridge Clay formation in England indicate a much larger taxon, possibly up to 15 metres (49 ft) long. However, these have not been assigned to the genus Liopleurodon.^[9]

A partial specimen of a jaw mandible measuring 2.875 metres (9.43 ft) is on display in the Oxford University Museum of Natural History: it is estimated that the total length of the jaw is in excess of 3 metres (9.8 ft). The specimen was originally assigned to the genus Stretosaurus (as Stretosaurus macromerus),.^[11] Stretosaurus later became a junior synonym of Liopleurodon.^[12] However, it was later re-classified as Pliosaurus macromerus.^[13]

In 1999, Liopleurodon was featured in an episode the BBC television series Walking with Dinosaurs, which depicted it as an enormous 25 m (82 ft) long animal. However, this is not considered to be accurate for any species of Liopleurodon.^[9]

Taxonomy

Phylogenetic position of Liopleurodon within Pliosauroidea

Liopleurodon belongs to the family Pliosauridae, a clade within Plesiosauria, known from the Jurassic (maybe also from the Cretaceous) of Europe and North America.^[14]

Liopleurodon was one of the basal taxa from the Middle Jurassic. Differences between these taxa and their relatives from the Upper Jurassic include alveoli count, smaller skull and smaller body size.^[8]

An analysis in 2013 classifies Liopleurodon, Simolestes, Peloneustes, Pliosaurus and Brachaucheininae as Thalassophonea.^[15]

References

External links

• Liopleurodon information and photos, The Plesiosaur Directory
• Article on the giant pliosaur skull once assigned to Liopleurodon, Tetrapod Zoology