Liopleurodon

Liopleurodon (, meaning 'smooth-sided teeth') is a genus of large, carnivorous marine reptile belonging to the Pliosauroidea, a clade of short-necked plesiosaurs. Two species of Liopleurodon lived during the Callovian stage of the Middle Jurassic Period (c. 160 to 155 mya), while the third, L. rossicus, lived during the Late Jurassic. It was the apex predator of the Middle to Late Jurassic seas that covered Europe.

Discovery and species
The genus name Liopleurodon was coined by H.E Sauvage in 1873, on the basis of very poor remains consisting of three large, 70 mm, teeth. One tooth was 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.

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.

Currently, there are three 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). From the Volgian of Russia, L. rossicus is known. This species was initially described by Novozhilov (1948) as belonging to Pliosaurus, and is the type species of the genus Strongylokroptaphus. Only L. ferox is known from more or less complete skeletons.

Paleobiology
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. Studies of the skull have shown that it could probably scan the water with its nostrils to ascertain the source of certain smells.

Size issue
Estimating the maximum size of Liopleurodon has become a controversial subject. The paleontologist L. B. Tarlo derived that the total body length of a pliosaur (including Liopleurodon) can be estimated from skull length, in which the skull is approximately one seventh of the entire body. The largest known skull belongs to L. ferox (1.5 meters in length), and according to Tarlo's estimation, this individual would be about 11 m (38 ft) long. However, as with its relative Kronosaurus, there is some uncertainty as to whether Tarlo's estimations are correct.

Recent studies on pliosaurs have cast doubt on Tarlo's estimations, and indicate that pliosaur skulls were about one-fifth of the total body length. Hence, the average size of the L. ferox would have ranged from 7 meters (23 ft) to 10 meters (33 ft) long.

The size estimate of Liopleurodon from the 1999 BBC series Walking with Dinosaurs, which depicts an enormous 25 meter-long Liopleurodon, is not considered to be accurate for any species of Liopleurodon.

Pliosaur remains excavated from Kimmeridge Clay Formation of England indicate a much larger taxon, possibly up to 15 meters (49.2 feet long), existed, however they have not been identified as being to Liopleurodon. A mandible on display in the Oxford University Museum of Natural History estimated over 3 meters (preserved 2.875m) was at one time classified as Liopleurodon macromerus. When the mandible was described, it was originally assigned to Stretosaurus (as Stretosaurus macromerus). The genus Stretosaurus later became a junior synonym of Liopleurodon. However, it has been re-classified as Pliosaurus macromerus.

The discovery of a very large pliosaur was announced in 2002, from Mexico, nicknamed the 'Monster of Aramberri'. A cautious estimate placed this juvenile at about 15 meters (49.2 ft) long. It was widely reported belonging to Liopleurodon, however no taxonomic conclusions could be made due to poor preservation and fact that the remains were of a partial vertebral column (non-diagnostic). The specimen was dated to the Kimmeridgian age of the La Caja Formation. =External links=


 * Liopleurodon genus info at The Plesiosaur Directory
 * Liopleurodon fact file from BBC, with pictures and video
 * Darren Naish, Tetrapod Zoology Blog entry on the giant pliosaur skull once assigned to Liopleurodon