Claw marks on a 100-million-year-old riverbed in China reveal how some dinosaurs doggy-paddled over long distances, scientists say.
"What we have are scratches left by the tips of a two-legged dinosaur's feet," study researcher Scott Persons, of the University of Alberta, said in a statement. "The dinosaur's claw marks show it was swimming along in this river and just its tippy toes were touching bottom."
Stretching over a distance of 50 feet (15 meters), the markings show that the dinosaur had a coordinated, left-right, left-right swimming style, Persons said. The researchers believe the scratches belong to a carnivorous theropod -- a type of dinosaur that walked on two legs -- that stood roughly 3 feet (1 meter) at the hip.
While it's tough to determine the identity of the swimming dinosaur from these marks alone, Persons suspects it could have been an early tyrannosaur or a Sinocalliopteryx, predators known to have roamed this prehistoric landscape in China.
The paddle-scratches were found in a dried-up river in China's Szechuan Province, which Persons described as a "dinosaur super-highway," full of the footprints of other Cretaceous-era theropods and long-necked, four-legged sauropods.