Swimming dinosaurs left tracks, scientists say

Ancient footprints have provided compelling evidence that some dinosaurs were able to swim, according to a new study.

Scientists discovered 12 consecutive prints left behind more than 125 million years ago in Spain's Camero Basin, an area that was once a vast lake.

The prints appear to have been left behind by a therapod, a type of dinosaur thought to have walked on two legs. The spacing and S-like shape of the prints suggested the dinosaur clawed at sediment on the lake floor while paddling upstream, the authors wrote in the June issue of the journal Geology.

"The dinosaur swam with alternating movements of the two hind limbs, a pelvic paddle swimming motion," said co-author Loic Costeur, a paleontologist at the University of Nantes, France.

"It is a swimming style of amplified walking with movements similar to those used by modern bipeds, including aquatic birds."

The six pairs of prints were little more than scratch marks, preserved in a layer of sandstone approximately 50 centimetres in length and 15 centimetres wide. The spacing between them suggests an underwater stride of 243 to 271 centimetres, the authors said.

A number of swimming reptiles, including ichthyosaurs and the long-necked plesiosaurs, lived during the same time period but are not considered dinosaurs.

But the question as to whether dinosaurs themselves swam has so far been difficult to prove, the authors contend, in part because of the difficulty in finding preserved evidence.