To answer the question of whether or not dinosaurs could swim, it is important to realize that not every prehistoric animal was a dinosaur. Certainly there were a lot of huge swimming creatures, such as Ichthyosaurus and Plesiosaurus, but these were not dinosaurs. Dinosaurs had four legs (not fins) and these legs are underneath their bodies, not out to the side in the manner of a swimming animal such as a whale or the earlier mentioned creatures. So, could actual Dinosaurs swim?
Until recently it was unknown if dinosaurs could swim or not. Even now it is uncertain that all dinosaurs could swim, although evidence has shown that at least some did. This evidence first came in 2004 when a fossilized set of markings were found in northern Spain.
What the fossil suggested is that a large meat eater swam across a water way in water slightly over 10 feet deep. This is indicated by foot prints which later became only small marks, indicating that the animal became buoyant as it propelled itself through the water. It also appears that the animal swam in a way that it pushed its lower limbs out to the side, much like ducks do. The animal was said to be swimming against a current and trying to maintain a straight line.
Later, in 2005, fossilized evidence came out of Wyoming where fossil foot prints of an ostrich sized dinosaur were found to be entering the water, where upon the tracks diminish and indicate that swimming began. The prints were made by a meat eater, although the species has not been determined, and might even be unknown.
Recent studies have also suggested that some dinosaurs had very lightweight bones, like those of birds. These bones were hollow and contained air sacks which certainly would be helpful to a large animal trying to stay afloat.
It is unlikely that all dinosaurs could swim, certainly they didn’t take to water without a reason. There is much fossil evidence showing where some dinosaurs likely died as the result of drowning in floods. In fact we owe drowning deaths to the reasons why we have so many intact fossilized skeletons. When a dinosaur died on land it was often eaten, torn apart, with its bones scattered and broken. When a dinosaur died in the water its body would eventually settle at the bottom to be covered by sediment, thus becoming a fossil if conditions are right. Its bones were usually not disturbed by larger meat eaters.
We know that many large animals of our time, including elephants, can swim, so why couldn’t these ancient beasts? As we wait for more fossils to be discovered we can certainly agree that some dinosaurs can, and did swim, just who those dinosaurs were, and why they went for a dip, is still a mystery.