We all know that dinosaurs walked the earth in prehistoric times, and many of us are also aware that pterosaurs flew across the skies and fearsome marine reptiles swam in the oceans. Some of these marine reptiles (which weren’t dinosaurs, despite what is frequently claimed) were large enough to rival the dinosaurs in size. This article concerns one of the largest and heaviest of them to have existed – Pliosaurus, an enormous oceanic behemoth measuring 35 feet long and weighing 12 tons which swam in the Jurassic seas around Europe (and possibly elsewhere) 154-147 million years ago.

Fossils of sea reptiles were nothing new to Europeans during the early 19th Century. The young British girl Mary Anning, who inspired the nursery rhyme “She sells seashells by the seashore”, uncovered many fossils along England’s southern coast including the dolphin-like ichthyosaur and the long-necked plesiosaur. In the 1820s, Reverend William Buckland – the same man who named the dinosaur Megalosaurus – discovered some intriguing fossils in Lincolnshire within the rocks of the “Kimmeridge Clay” dated to the late Jurassic Period approximately 154 million years ago. The holotype specimen is currently housed within the Oxford University Museum of Natural History (collection ID codes: OUMNH J.9245, OUMNH J.9247 through OUMNH J.9301 and OUMNH J.10453). These fossils were originally classified as a new species of Plesiosaurus, called Plesiosaurus brachydeirus. However, in 1842, the eminent British anatomist Sir Richard Owen reclassified the creature as a new genus and he renamed it Pliosaurus. The name was mistakenly mis-spelled – he intended to spell it as Pleiosaurus, derived from the ancient Greek pleion (πλείων) meaning “more/closer towards”, and sauros (σαυρος), “lizard”, because Owen believed that this newly-discovered creature was more closely related to modern-day lizards than Plesiosaurus was. However, according to prevailing naming conventions, because this was the name which was published first, even though it was spelled incorrectly, that’s the name that must be used.

Despite Owen’s assessment, it turns out that Pliosaurus wasn’t closely related to lizards at all. In fact, it was actually a close relative of the much smaller long-necked marine reptile Plesiosaurus, despite the two bearing little outward similarity. Plesiosaurus looks like a cross between a seal and a snake, whereas Pliosaurus looks like a gigantic long-jawed crocodile with flippers instead of legs.

Currently, the genus Pliosaurus encompasses six species (listed according to the year that they were named):

1. Pliosaurus brachydeirus (1842). Found in Market Rasen, Lincolnshire, England. Dated to the early part of the Kimmeridgian Stage of the late Jurassic Period, approximately 154 MYA.
2. Pliosaurus rossicus (1948). Found by the Volga River within the Chuvash Republic, Russia. Dated to the middle of the Tithonian Stage of the late Jurassic, approximately 147 MYA.
3. Pliosaurus funkei (2012). Formerly known by the nickname “Predator X”. Found on the Svalbard Islands, Norway. Dated to the middle of the Tithonian Stage, approximately 147 MYA.
4. Pliosaurus carpenteri (2013). Found in the Westbury Clay Pit, Wiltshire, England. Dated to the late Kimmeridgian Stage, approximately 151 MYA.
5. Pliosaurus kevani (2013). Found at Osmington Bay, Dorset, England. Dated to the early Kimmeridgian Stage, approximately 154 MYA.
6. Pliosaurus westburyensis (2013). Found in the Westbury Clay Pit, Wiltshire, England. Dated to the late Kimmeridgian Stage, approximately 151 MYA.

Additional species have been proposed; some of these have been refuted, while others are still of uncertain parentage.

The fragmentary remains belonging to each specimen make ascertaining the animal’s total length problematic. It is certain that Pliosaurus was a large animal, but claims which were made since at least the 1980s onwards of this creature measuring up to 40 feet long or even larger were later shown to have been exaggerated. Of the above-listed species, the Norwegian species Pliosaurus funkei was the largest, with an estimated length of 35 feet. The Russian species P. rossicus was only slightly smaller at an estimated 30-33 feet. By contrast, the species P. carpenteri measured 25 feet long, similar to that of the related genus Liopleurodon.

Below is a drawing which I made of Pliosaurus. The head is based upon the skull of Pliosaurus kevani, which is the best preserved. The body is based upon the fragmentary skeletal remains of all six species as well as the fossils of other pliosaur genera. The drawing was made with No.2 pencil and No.3 pencil on printer paper.

Pliosaurus. © Jason R. Abdale (August 18, 2023).

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Categories: Paleontology, Uncategorized

Tags: art, England, Europe, Jurassic Period, Late Jurassic, marine, Mesozoic, Norway, paleo-art, paleontology, plesiosaur, pliosaur, Pliosauridae, Pliosaurus, Prehistoric, reptile, Russia, United Kingdom