Pliosaurus (meaning ‘more lizard’) is a genus of thalassophonean pliosaurid known from the Kimmeridgian and Tithonian stages (Late Jurassic) of Europe and South America. Their diet would have included fish, cephalopods, and marine reptiles. This genus has contained many species in the past but recent reviews found only six to be valid, while the validity of two additional species awaits a petition to the ICZN. Pliosaurus currently consists of the type species P. brachydeirus, and also P. brachyspondylus, P. carpenteri, P. funkei, P. kevani, P. macromerus, P. rossicus and P. westburyensis, as well as the invalid P. portentificus. Most species of Pliosaurus are notable for their large body size, while the others, P. brachydeirus, P. brachyspondylus and P. portentificus, are known exclusively from immature individuals. Species of this genus are differentiated from other pliosaurids based on seven autapomorphies, including teeth that are triangular in cross section.
A specimen found in the Svalbard islands of northern Europe has 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. It is estimated to have lived approximately 147 million years ago and was named Pliosaurus funkei in Knutsen et al 2012, with estimated skull lengths of 160-200 cm and a forelimb legnth of 300 cm for the holotype (PMO 214.135), and an estimated skull length of 200-250 cm for the referred specimen (PMO 214.136), suggesting that the animal had proportionally bigger flippers than other pliosaurs compared to the skull size and dimensions of the vertebrae. 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.
Paleontologists believe that there were several reasons why this animal went extinct. First of all, Mosasaurs came on the scene at about this time and competed heavily with Pliosaurus for its main food source – fish. That’s because Mosasaurs were faster and agiler than Pliosaurus. They were also more vicious animals. This was just enough of an edge for them to out-compete Pliosaurus for fish. Second, water temperatures began to change during this time and this creature may not have been able to adapt quickly enough. Which is probably why this animal went extinct some 145 million years ago.