What are plesiosaurs and what do we know about their biology?

Plesiosaurs are extinct marine reptiles that existed at the same time as the dinosaurs, during the Mesozoic era (late Triassic to Cretaceous periods), from 200 to 65 million years ago.

They are unique in the known natural world as they used four flippers for propulsion although there has been much debate regarding their function.

For his PhD thesis, Dr Muscutt worked with teams at the Universities of Southampton and Bristol to provide a detailed analysis of plesiosaur propulsion.

The two types of plesiosaur

Although there are many different types of plesiosaurs, they can be loosely grouped into one of two main morphologies (body-plans):


• Long necks
• Small heads
• Usually pin-like teeth suitable for fish
• Small flippers compared to body
• Flippers are long and slender
• Are thought to be ambush predators that lunge
at shoals of fish


• Short necks
• Big heads
• Robust teeth suitable for large prey
• Large flippers compared to body
• Flippers are wide
• Are thought to be active pursuit predators which chase after large prey.

How would they swim?

It is thought that the different types of plesiosaur would use their flippers in different ways when hunting as they have different requirements.
Whilst hunting, plesiosauromorphs may drift around slowly for a long time, looking for fish and trying to remain undetected. This would require a flipper movement, or gait, that has a high efficiency, but wouldn’t need much thrust.
As active pursuit predators, pliosauromorphs would need to use a gait that has a high thrust, to be able to catch fast moving prey, but as the hunting time would be relatively short, a high efficiency would be less important.

Anatomy of a Flipper

The plesiosaur flippers are modified limbs specialised for aquatic locomotion. They have a streamlined profile and swept-back planform. The anatomy of the flipper is homologous (the same shape and structure) to the limb of any tetrapod, and we can compare the bones of the human arm to those in the plesiosaur flipper to highlight the similarity.

All plesiosaurs would have used their flippers in a motion that is primarily up-and-down (dorso-ventral) rather than forward-back. This motion is similar to the stroke of a turtle, penguin or sea lion, and can be modelled as simple harmonic motion.

The plesiosaur flippers are modified limbs specialised for aquatic locomotion. As only the bones remain as fossils, the soft tissue such as the muscles and skin must be reconstructed to obtain the shape. This was done by comparing the flippers of the plesiosaur to extant animals that swim using flippers such as turtles, sea-lions, and penguins.

Flippers were 3D printed in ABS with dye injection ports, they are around 1.2 scale.