Plesiosaur - Behavior

Behavior

Pliosaurs were top carnivores in their respective foodwebs. They were pursuit predators of various sized prey and opportunistic feeders, their teeth were used to pierce small soft-bodied prey, especially fish. Hard and soft-bodied cephalopods also formed part of the diet of all plesiosaurs. Plesiosaurs hunted visually and perhaps employed a directional sense of olfaction. They had powerful jaws, probably strong enough to bite through the hard shells of their prey. The bony fish (Osteichthyes), started to spread in the Jurassic, and were likely prey as well. Recent evidence seems to indicate that some plesiosaurs may have, in addition, been bottom feeders. Plesiosaurs were also prey for other carnivores as shown by bite marks left by a shark that have been discovered on a fossilized plesiosaur fin and the fossilized remains of a mosasaur’s stomach contents that are thought to be the remains of a plesiosaur.

It had been theorised that smaller plesiosaurs may have crawled up on a beach to lay their eggs, like the modern leatherback turtle, but it is now clear that plesiosaurs gave birth to live young: The fossil of a pregnant plesiosaur Polycotylus latippinus shows that these animals gave birth to one large juvenile and probably invested parental care in their offspring, similar to modern whales.

Another curiosity is their four-flippered design. No modern animals have this swimming adaptation (sea turtles only swim with their front flippers), so there is considerable speculation about what kind of stroke they used. While the short-necked pliosauroids (e.g. Liopleurodon) may have been fast swimmers, the long-necked varieties were built more for maneuverability than for speed. Skeletons have also been discovered with gastroliths in their stomachs, though whether to help break down food in a muscular gizzard, or to help with buoyancy, or both, has not been established. However, the total weight of the gastroliths found in various specimens appear to be insufficient to modify the buoyancy of these large reptiles.