THE FAMOUS giant marine creatures of the Jurassic and Cretaceous periods - plesiosaurs such as Liopleurodon - were not actually dinosaurs, but members of distantly related reptile groups.
But although there were no aquatic specialists among the dinosaurs, most could probably swim, at least in a rudimentary fashion. The majority of living animals are able to swim - or at least paddle - if they find themselves in the water. Just do a quick YouTube search for swimming dogs to see a few cute examples (and while you're there, check out the latest Walking With Dinosaurs videos from the BBC Earth Unplugged YouTube site!).
So it's likely that many dinosaurs could swim based on what we know of living animals. There is also a second line of evidence: footprints. There are many examples of strange dinosaur footprints that appear in rocks that were formed underwater in lakes, not on land.
These footprints are usually not imprints of the entire foot, but only the tips of the claws. They are thought to have been formed by a swimming dinosaur whose feet were scratching the bottom of the lake. Just think of your own experiences in a swimming pool, when your feet accidentally sweep across the bottom of the pool during a swim, or when you push off the bottom to help yourself move through the water. This is probably what these dinosaurs were doing when they left these footprints. The picture above shows a Eustreptospondylus swimming in the sea in a scene from Walking With Dinosaurs.
– Steve Brusatte, Resident Palaeontologist