Twelve footprints found in the bed of an ancient lake in northern Spain have thrown up the first compelling evidence that some land dinosaurs could swim, researchers reported on Thursday.
The 15m-long track in sandstone ”strongly suggests a floating animal clawing the sediment” as it swam against a current, they say.
The swimmer is believed to have been a therapod — the vast family of carnivorous dinosaurs that included the mighty Tyrannosaurus rex — that lived in the Early Cretaceous, about 125-million years ago.
The track way in the former lakebed consists of six asymmetrical pairs of two or three S-shaped scratch marks. Each set measures about 50cm in length and 15cm wide.
The prints paint a beguiling picture of a large, buoyant dinosaur whose clawed feet raked the sediment as it swam in a depth of about 3,2m of water, according to the paper, which appears in the June issue of the United States journal Geology.
Ripple marks on the surface of the site indicate the dinosaur was swimming against a current, struggling to maintain a straight path.
”The dinosaur swam with alternating movements of the two hind limbs, a pelvic paddle-swimming motion,” said co-author Loic Costeur, of the Laboratory for Planetology and Geodynamics at the University of Nantes, western France. ”It is a swimming style of amplified walking, with movements similar to those used by modern bipeds, including aquatic birds.”
The question of whether dinosaurs could swim has been debated for years. Until now, no firm evidence had come to light, just mysterious ”ghost traces” at various sites.
Asked to speculate as to which dinosaur may have made the tracks, Costeur cautiously pointed to the allosaurus — a bipedal carnivorous dinosaur with a large skull balanced by a long, heavy tail. Some allosauruses could reach more than 10m in length.
The discovery opens up new avenues in dinosaur research, said Costeur.
Computer modelling will be able to reveal more about anatomy and biomechanics, ”as well as our view of the ecological niches in which they lived”.
The Virgen del Campo track is located at the Cameros Basin in La Rioja, at the site of a delta to a former lake. The basin is already known as a treasure trove of footprints of walking theropods.
The lead author is Ruben Ezquerra of the Foundation for Palaeontological Patrimony in La Rioja. — Sapa-AFP