Temporal range: Late Jurassic
Reconstruction of Pliosaurus kevani by Mark Witton
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: Sauropterygia
Order: Plesiosauria
Family: Pliosauridae
Subfamily: Brachaucheninae
Genus: Pliosaurus
Owen, 1842
Type species
Pliosaurus brachydeirus
Owen, 1842
Referred Species
  • P. brachydeirus (Owen, 1841)
  • P. carpenteri (Benson, 2013)
  • P. funkei (Knutsen, 2012)
  • P. kevani (Benson, 2013)
  • P. rossicus (Novozhilov, 1948)
  • P. westburyensis (Benson, 2013)
  • Plesiosaurus giganteus
  • Plesiosaurus recentior
  • Liopleurodon rossicus

Pliosaurus is an extinct genus of thalassophonean pliosaurid from the Late Jurassic period. As one of the largest plesiosaurs of all time, it was an apex predator of the Kimmeridgian oceans, preying upon the numerous fish, marine reptiles, and cephalopods in its habitat. There are currently six valid species: P. funkei, P. rossicus, P. brachydeirus (type species), P. carpentri, P. kevani, and P. westburyensis.


Like other plesiosaurs, Pliosaurus had four powerful flippers used to propel itself underwater. Analysis of the flipper bones from the animal shows that it cruised using only two fore-flippers, using the back pair for extra speed when pursuing its prey. Its head was very large, with skull length estimates for P. funkei reaching 2-2.5 meters (6.6-8.2 feet). The animal also had a very powerful bite force. 2014 bite force estimates for P. kevani produced varying results from 9,617–16,927 N (981–1,726 kgf; 2,162–3,805 lbf) at the anterior dentary tooth to 27,685–48,728 N (2,823–4,969 kgf; 6,224–10,954 lbf) at the 36th dentary tooth pair. The larger P. funkei would have probably had a bite force comparable to Tyrannosaurus, if not larger.


The type species of the genus, P. brachydeirus, was first described and named by Richard Owen in 1841, as a species of Plesiosaurus (at the time a wastebasket taxon) in its own subgenus Pleiosaurus. In a later study from Owen that relocated the species to its own genus, Pleiosaurus was misspelled as Pliosaurus, and the latter name stuck due to rules from several articles of the ICZN. Pliosaurus means "more lizard" in Greek, in reference to Owen's belief that the animal was more closely related to "saurians" such as crocodiles than Plesiosaurus was.

The most famous species, P. funkei, was discovered in the Svalbard archipelago of Norway. Due to its relative completeness and large size, it was dubbed "Predator X" before its official description and gained extensive media coverage. Due to the freezing climate of the Arctic regions, the fossils had to be subjected to freeze-thaw cycles before collection.


Of the several species of Pliosaurus, two are considered dubious: P. brachyspondylus and P. macromerus, while another one (P. portentificus) is considered undiagnostic. Pliosaurus as a genus is different from other pliosaurs due to seven autapomorphies, including teeth that are triangular in cross section. As a member of the clade Thalassophonea, Pliosaurus diverged from the Brachaucheninae group of pliosaurs, which went on to produce the Cretaceous short-necked plesiosaurs Kronosaurus and Megacephalosaurus.


Pliosaurus is known from Late Jurassic rock formations from throughout Europe and South America, including the Kimmeridge Clay of England and Svalbard in Norway. The animal would have lived in the tropical epicontinental seas that covered much of the planet during the Jurassic. It survived alongside a variety of other marine reptiles, including the plesiosaurs Kimmerosaurus and Colymbosaurus, the ichthyosaur Ophthalmosaurus, the ocean crocodiles Metriorhynchus and Dakosaurus, and the sea turtles Plesiochelys and Thalassemys. Most of these animals would have likely fallen prey to Pliosaurus, which was the undisputed apex predator of its ecosystem.


The largest species of Pliosaurus, P. funkei, was originally estimated at 15 meters (49 feet) long and weighing up to 45 metric tons (50 short tons). Through more analyzation of the specimen, which was discovered in the Svalbard archipelago of Europe, the size was decreased down to 10-13 meters (33-43 feet) long. The skull length of the P. funkei holotype has been estimated at 1.6-2 meters (5.2-6.6 feet), which suggests that it had proportionally larger flippers than other pliosaurs compared to the skull size and vertebrae dimensions. Overall, P. funkei was one of the largest pliosaurs of all time, comparable in size to the Cretaceous genus Kronosaurus. P. carpentri had a length of about 8 meters (26 feet) and a weight of 5 metric tons (5.5 short tons), while P. rossicus was around 10 meters (33 feet) long and weighed 11 metric tons (12 short tons).

In popular media[]

  • Pliosaurus funkei was featured in the fourth episode of the BBC documentary, Planet Dinosaur, under its nickname "Predator X". It hunted a pod of Kimmerosaurus several times before finally succeeding in killing one.
  • Pliosaurus appeared in Jurassic World: The Game.
  • Pliosaurus appeared in Jurassic Park Builder, as a limited edition piscivore.
  • Pliosaurus appeared on Dinosaur Train.
  • Pliosaurus appeared in the Netflix Original Documentary Series, Life on Our Planet, where it was featured hunting sea turtles.
  • A possible new species of Pliosaurus was found in 2023 and was featured in the BBC documentary Attenborough and the Giant Sea Monster.