Plesiosaurus is often mistakenly referred to as a dinosaur, when in fact it is a prehistoric marine reptile that lived at the same time as the dinosaurs. It had a long neck, four paddle-like flippers and a tail.
Plesiosaurus would have roamed the vast seas of the Jurassic.
Plesiosaurus is likely to have had similar hearing to that of the whales and dolphins of today.
The Plesiosaurus' mouth was the perfect fish trap: it had simple needle-like teeth curved around its U-shaped jaw.
The nostrils of Plesiosaurus were positioned closer to its eyes than the tip of its snout.
The most fantastic find was a plesiosaur uncovered in 1987. Its abdomen contained bones of an embryo, which proves the animal gave birth to live young. Plesiosaurs gave birth to just one individual, allowing us to make inferences on the degree of maternal care.
Height: 1m (3.28ft)
Length: 3.5m (11.48ft)
Weight: 449.96kg (992lbs)
Top speed: 16.5kph (10.25mph)
Vision: Plesiosaurus' eyes were positioned to the sides of their head, looking upwards so they could ambush their prey from below.
Skin: Plesiosaurs had smooth skin to reduce drag in the water.
Brain: Plesiosaurs had smaller brains relative to body size than most dinosaurs.
Prey: From the stomach contents of the plesiosaurs, we can tell they fed on belemnites and ammonites as well as prehistoric fish.
Bite: Plesiosaurus could use its long neck to sneak up on its prey from a distance with little chance of being detected.
Nest: Plesiosaurs are known to have given birth to a single live offspring, just like us. An unborn plesiosaur would have been 1.5m (5ft) long – that's a whopping one third of its mum.