The first definitive evidence that dinosaurs could swim has been discovered by scientists.

A remarkable trackway of scratches made by a creature’s claws as it dino-paddled in shallow water about 125 million years ago has proved that some predatory dinosaurs were not afraid to get their feet wet.

While many prehistoric sea beasts have long been known to science, such as ichytyosaurs and the plesiosaurs that gave rise to the legend of the Loch Ness Monster, these were not true dinosaurs but aquatic cousins.

Dinosaurs were adapted to a life on land, and the question of whether some could also swim has been controversial, with little firm evidence in either direction.

The 15-metre trackway identified in Spain could now settle the issue, providing the first long and continuous record of swimming by a dinosaur.

It consists of six asymmetrical paired sets of scratchmarks preserved in sandstone. Each set of two or three scratches is about 50cm long and 15cm wide, suggesting that they were left by the claws on the dinosaur’s hind legs as they scraped the bottom while it swam.

The fact that scratches rather than full prints have been preserved shows that the dinosaur was swimming and not wading, as the weight of its body must have been supported by water. Ripples on the surface of the sandstone also suggest a depth of about 3.2 meters.

Details of the discovery at La Virgen del Campo in the Cameros Basin in northeast Spain, are published in the journal Geology.

Loic Costeur of the University of Nantes in France, who led the research team, said that while it was impossible to identify the species of dinosaur that made the prints precisely, it is clear it was a bipedal predatory dinosaur or theropod. The depth of the water suggests it stood between 1.5m and 3m tall.

“It was a large carnivore like the tyrannosaurs, though it wasn’t actually a tyrannosaur,” Dr Costeur said. “The most abundant kind of predators in this area at this time were the allosauroids, so that’s what we postulate it might have been.”

Previous research has shown that some predatory dinosaurs, particularly the spinosauroids, ate a diet that included fish, but there is no evidence of this for allosauroids.

As the prints flow in an slight S-shape, scientists have suggested that the dinosaur might have been swimming against a current, and struggling to maintain its direction in a straight line.

“It is tempting to speculate that it might have been hunting, but we cannot say that for certain from the evidence.”

The swimming motion of the dinosaur seems to have been similar to that used by modern aquatic birds, which probably reflects the prevailing theory that birds are descended from theropod dinosaurs.

“The dinosaur swam with alternating movements of the two hind limbs, a pelvic paddle swimming motion,” Dr Costeur said. “It is a swimming style of amplified walking with movements similar to those used by modern bipeds, including aquatic birds.

“The trackway at La Virgen del Campo opens the door to several new areas of research. New biomechanical modelling will increase our understanding of dinosaur physiology and physical capabilities, as well as our view of the ecological niches in which they lived.”

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