A new fossil reptile suggests that bipedalism may be more common than previously thought--but not necessarily a sure route to evolutionary success. The 25-centimeter-long herbivore, christened Eudibamus cursoris, was dashing around on two legs as many as 80 million years before the first dinosaur, much earlier than most paleontologists suspected.
When amphibians first sloshed ashore, some 360 million years ago, they waddled like soldiers crawling under barbed wire. Even after reptiles began to inhabit drier climes, they plodded on all fours using the same sprawled stance. Paleontologists thought that the pace didn't pick up until fleet-footed bipedal dinosaurs appeared in the Late Triassic, about 210 million years ago.
Now a 290-million-year-old fossil discovered in 1993 in a quarry near Gotha, Germany, breaks that record. "What's really exciting is that this fossil is the first instance of an animal built for speed," says Robert Reisz of the University of Toronto in Mississauga, Ontario, Canada, who introduced the new species in the 3 November issue of Science. Eudibamus had hindlimbs that were 64% longer than its forelimbs and 34% longer than its trunk, proportions comparable to those of modern lizards that run on two legs. The reptile had also evolved a kind of knee joint that allowed it to run with its feet directly underneath its body. Both shinbones in Eudibamus fit onto the end of the femur, forming a hingelike joint that puts all of the leg in one plane, just as in humans and dinosaurs. The result is an energy-efficient posture that allows the bones, not just muscles, to help support the animal's weight.
But bipedalism didn't guarantee Eudibamus a future. "Clearly for this little guy, it didn't make much of a difference," says Hans-Dieter Sues of the Royal Ontario Museum in Toronto. "This was a very short-lived evolutionary lineage, as far as we know." Michael Caldwell of the University of Alberta in Edmonton suspects that bipedalism may have evolved many times in vertebrate history before dinosaurs, birds, and primates made the innovation an evolutionary success. In giving lug-necked predators a run for their money, Eudibamus may have been just one of any number of creatures darting briefly ahead of their time.