When dinosaurs were around, there were lots of different kinds of creatures that lived in the water.
Many of the known swimmers from this time were actually types of reptiles. One good example of an animal like this was the Plesiosaur, which had four fins and spent its time in the water looking for fish to eat. Another reptile that was already living in the water when the dinosaurs were around was the crocodile!
Although it’s hard to know for sure, new archaeological findings also make it seem likely that some dinosaurs might have been capable of swimming, too. This theory is based on recent fossils that show scratches on the bottom of bodies of water that might have been caused by the paddling feet of an animal such as the T-Rex! Fossils of the Arenysaurus, a dinosaur that archaeologists believe lived close to the shore, show that this type of dinosaur also had strong limbs that some scientists believe would have been used for swimming in the nearby water!