SCIENCE/AAAS, IBRAHIM ET AL.An odd carnivorous dinosaur may have been the earliest land animal to adapt to the life aquatic. With flat-bottomed feet for pedaling, dense bones to regulate buoyancy, and retractable nostrils far back in its skull, Spinosaurus aegyptiacus may have hunted its prey both on land and in lakes and rivers. Its semi-aquatic lifestyle was revealed by an analysis of disparate fossil bones assembled into the most complete spinosaur skeleton, described last week (September 11) in Science.
Paleontologist Nizar Ibrahim of the University of Chicago and his colleagues stumbled upon some of the bones used in this study in a museum in Milan; others were collected by a freelance fossil hunter in Morocco, who led the researchers to a site where they found more remains. These specimens, past descriptions and digital models suggested that 50-foot-long spinosaurs may have hunted in North African waterways approximately 97 million years ago.
Its small pelvis and short hind limbs suggested that S. aegyptiacus may have walked on all fours and had a more forward-positioned center of gravity. Coupled with the foot and bone adaptations proposed, the adaptations would have made it a fearsome swimmer. But the authors wrote in their paper that one of its most prominent features—a giant sail-like structure on its spine—was probably just for display.
“There’s no doubt in my mind that Spinosaurus would have done most of its hunting in the water,” Ibrahim told Nature. Study coauthor Paul Sereno told The Christian Science Monitor that the dinosaur likely paddled with its hind legs, but its propulsive tail resembled that of a crocodile. “It's a chimera, half duck and half crocodile,” he said.
“An extinct animal that we already thought was kind of weird was actually even stranger,” Lawrence Witmer of Ohio University in Athens told Science News.
The splashy discovery hasn’t convinced everyone that spinosaurs could swim, however. On Twitter, John Hutchinson of the Royal Veterinary College of the University of London noted that “most dino tails are good for swimming.” In a blog post, paleontologist Scott Hartman described the new study as “an important contribution,” but cautioned that the smaller hind limbs and pelvis could be from juvenile animals.
“It’s really exciting speculation, but I’d like to see more-conclusive evidence,” Hutchinson told Nature.