Dinosaurs must have lived in water, scientist claims He added: "Earlier theories have suggested they might have swum, or lived in swamps; and much work has been done to show them wading into streams to catch fish. My view is different. I argue that they must have evolved in shallow water. It's not that they could manage to cope with it, or that they swam, or even that they were submerged; but that they lived in water that supported their weight.