Paleo Profiles: Pliosaurus

At the very start of this year, (2024), a BBC documentary starring David Attenborough discussed the discovery of a beautifully preserved skull of a giant marine reptile called a pliosaur. Pliosaurs were apex predators in the oceans of the Mesozoic era, with many people recognising them for Liopleurodon appearing in the documentary Walking with Dinosaurs (1999). This skull most likely belonged to Pliosaurus, the genus that the family is named after, and the documentary suggests that it could belong to a new species of Pliosaurus. Today we’ll be looking at the life of these sea monsters.

Discovery and Fossils

Kenneth Carpenter’s photo of P. rossicus, from wikipedia.org

Pliosaurus was discovered during a period when modern palaeontology was emerging as a science. Fossils of long extinct giant, and some small, reptiles were being found in the rocks of Britain, France, and Germany. Some of these were grouped together in 1841 by Richard Owen under the term ‘dinosaurs’ but they were not the only ones – the flying bird-like reptiles were called ‘pterosaurs’ and the aquatic reptiles were split into the long-necked plesiosaurs, the dolphin-like ichthyosaurs, and the snake-like mosasaurs. William Buckland, the same man who found the first dinosaur Megalosaurus, found a marine reptile and believing it to be a member of the genus Plesiosaurus named it as a new species. In 1842 Richard Owen would again look at Buckland’s work and judged this species to be more lizard-like than other plesiosaurs so named it Pliosaurus brachydeirus – ‘More lizard’ as it was ‘more like a lizard.’ We actually know now that this is inaccurate, but more on that later. Owen also misspelled his fossil – he originally meant to spell it Pleiosaurus but that little mistake came to define a sea monster.

There is some debate about how many species of Pliosaurus there actually is as dealing with, at times fragmentary, bone means it can be difficult to accurately determine whether or not a specimen is a unique individual, species, or genus. There are six recognised species of Pliosaurus: P. brachydeirus from Lincolnshire, England; P. rossicus from Russia; P. funkei from Svalbard, the Arctic islands north of Norway; P. carpenteri and P. westburyensis both from the Westbury Clay Pit in England; and P. kevani from Osmington Bay, England. This new fossil find was found by collectors Steve Etches and Phil Jacobs while walking on the beach near Kimmeridge Bay, an area known for Jurassic fossils, where they found part of the skull. Telling the nearby museum the rest of the skull was dug out from the side of a cliff! Just over a decade ago you might have heard the pliosaur ‘Predator X’ – a truly gigantic animal with an unintentionally cool name. It was obviously a predator and ‘X’ is used to mean ‘unknown’, so as it was an unknown predator it became known as Predator X until 2012 when it was officially given the name Pliosaurus funkei. Excavated over several expeditions the freezing conditions on Spitsbergen, Svalbard meant the fossils had fragmented into thousands of pieces which researchers painstakingly pieced back together. There are potentially four other species, (P. macromerus, P. almanzaensis, P. patagonicus, and P. brachyspondylus), but are awaiting reclassification, and two other species have been found to belong to already established species.

Biology

A reconstruction from David Attenborough and the Giant Sea Monster

In Walking with Dinosaurs they portrayed a Liopleurodon as being 25 metres (82 feet) in length which is oversized to say the least – Liopleurodon reached 7 metres (23 feet) so while still large it did not reach that size. Pliosaurs were huge and so was Pliosaurus. The smaller species, like P. brachydeirus and P. kevani, reached between 8 and 10 metres (26-33 ft) in length, with P. funkei and the new specimen to reach up to 12 metres (39 feet) in length! These behemoths were the size of buses and the largest were twice the length of killer whales. They were also heavy with an estimated 5.5 metric ton mass, not as much as an adult male orca but we also have to remember that orcas have that weight due to blubber. Pliosaurus lived in much warmer waters so did not need insulation. To put their size into perspective the larger species had skulls 2 metres (6.5 feet), so I certainly would be a mouthful if I was an unlucky swimmer in Jurassic England.

Reconstruction of P. funkei, from wikipedia.org

Pliosaurs and Pliosaurus, despite what Richard Owen thought, were not related to lizards, and are in fact a branch of the plesiosaur order. Plesiosaurs were four flippered aquatic reptiles with plesiosauridae, perhaps the most famous family, were the long-necked, ‘Loch Ness Monster’ reptiles. Pliosaurs were short-necked and apex predators. Pliosaurus had a jaw full of interlocking teeth, about 130 of them, that were serrated making it easy of them to punch through flesh and fat. They also had a powerful bite, estimated to be 33,000 newtons; in comparison the animal with the strongest bite force today is the saltwater crocodile with 16,460 newtons. A scan of the skull done for the David Attenborough documentary found that the snout was covered in blood vessels indicating that it had a fantastic sense of smell. With this and their large size it is not surprising that Pliosaurus was top of the food chain. Their jaws and teeth were capable of biting through any animal, and wounds on other animals match the teeth of Pliosaurus. Smaller pliosaurs and plesiosaurs, sharks, giant fish, ichthyosaurs, ammonites, diving pterosaurs, squid, and sea crocodiles could all be on the menu.

Palaeontologists have tried to work out how Pliosaurus and plesiosaurs in general swam. Since the 1800s palaeontologists have tried to work out if they swam like a rower or if they used all their flippers to swim. Using a mixture of computer modelling and robots we are beginning to understand how they swam. Utilising both sets of flippers it would propel them through the water, but to avoid vortices created by the front set the back set would alternatively flap avoiding the front vortices. It also allowed plesiosaurs to swim very quickly, and the short neck of Pliosaurus made them very efficient. This giant predator was fast, albeit not very manoeuvrable while its plesiosaur prey was slower but more agile. It is likely that they gave birth to live young, whether they cared for their offspring is another question. A 2012 paper analysed a skull at the time attributed to the then valid species of P. brachyspondylus found it was suffering from arthritis on its jaw! We have not managed to find out how old the pliosaur was, but it probably was painful for the elderly pliosaur.

When and Where

Pliosaurus were found in the Kimmeridge and Tithonian epochs of the Late Jurassic, around 155 to 147 million years ago. If all potential species are accepted then they were found in Europe and South America, but with the confirmed species they were mainly found in England, Svalbard, and Russia. Pliosaurs were likely warm-blooded so probably swim in cold waters, but Europe at this time was made up of a warm sea. Europe would likely have been either a tropical or sub-tropical area, so we would expect them to be right at home in the modern Caribbean.

Bibliography:

• Darren Naish, Ancient Sea Reptiles: Plesiosaurs, ichthyosaurs, mosasaurs and more, (London: Natural History Museum, 2022)
• David Attenborough and the Giant Sea Monster, Produced by Victoria Bobin, BBC, (01/01/2024)
• Riley Black, ‘Paleontologists Reveal the Identity of “Predator X”‘, National Geographic, (15/10/2012), [Accessed 08/01/2024]
• David Martill, Megan Jacobs, and Roy Smith, ‘A truly gigantic pliosaur (Reptilia, Sauropterygia) from the Kimmeridge Clay Formation (Upper Jurassic, Kimmeridgian) of England’, Proceedings of the Geologists’ Association, 134:3, (2023), 361-373
• Espen Knutsen, ‘A taxonomic revision of the genus Pliosaurus (Owen, 1841a) Owen, 1841b’, Norwegian Journal of Geology, 92, (2012), 259-276
• Jason Abdale, ‘Pliosaurus’, Dinosaurs and Barbarians, (18/08/2023), [Accessed 06/01/2024]
• Judyth Sassoon, Leslie Noe, and Michael Benton, ‘Cranial anatomy, taxonomic implications and palaeopathology of an Upper Jurassic Pliosaur (Reptilia: Sauropterygia) from Westbury, Wiltshire, UK’, Palaeontology, 55:4, (2012), 743-773
• Ben G Thomas, ‘Predator X – The Giant Arctic Pliosaur’, YouTube.com, (25/12/2020), [Accessed 10/01/2024]

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