In the dark red dirt of Madagascar, scientists have unearthed what they claim are the oldest dinosaur fossils ever found. The find, reported in tomorrow's issue of Science (22 October, p. 763 ), includes bones from two new species of dinosaurs and at least eight other previously unknown species of prehistoric creatures. The researchers say the remains may provide key insights into a little-known phase in the evolution of dinosaurs and mammals.
The team, led by paleontologist John Flynn of The Field Museum in Chicago, came across the fossils with the help of a young man in a remote Madagascar village. When they asked if anybody in the village knew of any old, buried animal bones nearby, he led them to a hill full of fossils. Since then, the researchers have spent several field seasons excavating this treasure trove. Among the items they found were jawbones from two new, primitive dinosaur species belonging to a group called the prosauropods.
Until now, the title for the earliest known dinosaur has been jointly held by two species, Herrerasaurus and Eoraptor, both discovered in Argentina. Using radioisotopic dating of underlying volcanic deposits, researchers in 1993 estimated them to be 228 million years old. Flynn's team was unable to date the Madagascar fossils by the same technique, because there aren't any volcanic beds there. Nearby, however, the team discovered fossils of two animals, a primitive parrot-beaked reptile and an early relative of mammals, that are both believed to have lived several million years before Herrerasaurus and Eoraptor. From their proximity, the team concludes that the dinosaurs have to be similarly old.
The site should shed more light on the Triassic, a period from which relatively few fossils are known. Earth's fauna was changing rapidly at the time, says team member J. Michael Parrish of Northern Illinois University in DeKalb; many primitive reptile species declined or went extinct, while other animals, most notably the dinosaurs, became more numerous and diverse. "We've probably found a time slice of the Triassic that has never been seen before," says Parrish. For many fossils, he says, "we are still scratching our heads about what they are."
"Any specimens from these earlier time horizons are interesting," says paleontologist Paul Sereno of the University of Chicago, who discovered the Argentinean dinosaurs. But he is not yet willing to concede that his record has been broken. Dating fossils by looking at other specimens nearby is imprecise, he says, and "I don't think the evidence is clear that these are older."