Temporal range: Late Jurassic, 155.7–150.8Ma
|P. macromerus jaw, Natural History Museum|
Pliosaurus (meaning 'more lizard') is a genus of extinct marine reptile. It is included in the family Pliosauridae. Its diet would have included fish, squid and other marine reptiles. This genus has contained several species in the past but it currently consists of the type species P. brachydeirus, the others being P. brachyspondylus, P. portentificus, the very large P. macromerus and P. funkei, and P. rossicus, which lived during the Late Jurassic. Unlike other pliosaurids, Pliosaurus have teeth that are triangular in cross section.
Discovery and species 
Currently there are four to six recognized species of Pliosaurus, four of which are known from the Kimmeridge Clay Formation of England. Which ones of the species listed below are recognized as valid depends on the author:
Pliosaurus portentificus is known from the late Kimmeridgian of England. Considered by Knutsen (2012) to be a nomen dubium, with its holotype specimen most likely being a juvenile individual of one of the other species of Pliosaurus
Pliosaurus rossicus is a relatively small pliosaur known from two specimens discovered in Chuvashia, Russia. Knutsen (2012) provisionally retained it as a separate species, but stressed that further examinations are needed to determine whether P. rossicus is indeed a separate taxon or merely a junior synonym of Pliosaurus macromerus. This species was described in 1948 as a species of Pliosaurus; subsequently it was made the type species of the genus Strongylokroptaphus, and later was assigned to the genus Liopleurodon before being assigned to the genus Pliosaurus again by Knutsen (2012).
The sixth species, Pliosaurus funkei, is known from Svalbard. Also known as "Predator X", the species is known from a partial skull, a complete flipper and some assorted remains, including a section of vertebra of two individuals was excavated in mid-2008 in Svalbard, near the Arctic, by a Norwegian team led by Dr. Jørn Hurum. It is claimed by researchers to be the "most fearsome animal ever to swim in the oceans." The remains were discovered in June 2006 during a two-week expedition led by Dr. Hurum of the Natural History Museum at the University of Oslo. The team found 20,000 fragments of the creature's skeleton, which is being preserved and assembled at the museum. Due to the distribution pattern of pliosaurs, scientist believe that species were cosmopolitan, like some groups of modern-day whales.
Using Liopleurodon, another large pliosaurid, as a guide, the Svalbard specimen had been estimated to have been 15 metres (49 ft) long, 45,000 kilograms (99,000 lb) in weight and had teeth 30 centimetres (12 in) long. The jaws of the creature may have been able to exert more force than those of a Tyrannosaurus rex, with one news source stating the bite was over 10 times more powerful than any modern animal and four times more powerful than that of a Tyrannosaurus. It is estimated to have lived approximately 147 million years ago. Analysis of bones from the four flippers suggest that the animal cruised using just two fore-flippers, using the back pair for extra speed when pursuing and capturing prey. P. funkei's brain was of a similar type and size, proportionally, to that of today's great white shark, the team says. Later on, thorough scrutiny of this Svalbard specimen revealed that it was not as massive as originally claimed; total length estimate have been revised to 10.0–12.8 metres (32.8–42.0 ft).
- 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 029-196X. Low resolution pdf High resolution pdf
- Noè, L. F., Smith, D. T. J. & Walton, D. I. (2004). "A new species of Kimmeridgian pliosaur (Reptilia; Sauropterygia) and its bearing on the nomenclature of Liopleurodon macromerus". Proceedings of the Geologists' Association 115, 13-24.
- Espen M. Knutsen (2012). "A taxonomic revision of the genus Pliosaurus (Owen, 1841a) Owen, 1841b". Norwegian Journal of Geology 92 (2–3): 259–276. ISSN 029-196X. Low resolution pdf High resolution pdf
- Novozhilov, N.I. (1948). "Two new pliosaurs from the Lower Volga Beds Provolzhe (Right bank of Volga)". Doklandy Akadamie Nauk SSSR, Moscow 60: 115–118.
- Novozhilov, N.I. (1964). "Order Sauropterygia". Osnovy Paleontologii 12: 309–332.
- Halstead, L. Beverly (1971). "Liopleurodon rossicus (Novozhilov) - a pliosaur from the Lower Volgian of the Moscow basin". Palaeontology 14: 566–570.
- "Arctic sea monster's giant bite". BBC. 2009-03-17. Retrieved 2009-03-17.
- Smith, Lewis (2009-03-17). "Predator X was the most fearsome animal ever to swim the oceans". London: The Times. Retrieved 2009-03-17.
- "Predator X: monster of the deep". Cosmos Magazine. 2009-03-31. Retrieved 2009-03-31.
- Alleyne, Richard (2009-03-17). "Biggest and smallest prehistoric predators unearthed". London: The Daily Telegraph. Retrieved 2009-03-17.
- Coghlan, Andy (2009-03-17). "Fossil of 'ultimate predator' unearthed in Arctic". New Scientist. Retrieved 2009-03-17.
- "Gigantic fossils of ‘Predator X’ found in the Arctic". Russia Today. 2009-03-17. Retrieved 2009-03-17.
- "Fossil 'makes T-Rex look feeble'", news24.com, 17 March 2009.
- Damien, Gayle (2012-10-17). "The mystery of Predator X - the most fearsome of all prehistoric monsters (which turns out to be not quite as scary as we thought)". USA: Mail Online. Retrieved 2012-10-17.
- Gigantic Pliosaurus discovered on Norwegian soil
- Pliosaurus - Naturhistorisk museum
- Sea Monsters: A Prehistoric Adventure Movie - Interactive Time Line - National Geographic
- Britannica Online Encyclopedia