Malagasy rift teems with prize fossil fauna.

Unsurpassed in biodiversity, and home to all of the world's lemurs, Madagascar has earned distinction as prime territory for the study of living organisms. The island may become equally famous as a hunting ground for fossils, a study in the Oct. 22 SCIENCE suggests.

A team of American and Malagasy paleontologists has identified a potential mother lode of Triassic fauna, documenting a pivotal and little understood period of evolution. The researchers have unearthed exquisitely preserved skulls and bones from mammal-like reptiles, along with fragments of what may be the oldest dinosaurs yet discovered.

The fossils excavated so far represent land animals from around 230 million years ago, during the middle-to-late Triassic period. Around this time, early dinosaurs established what was to become a 150-million-year dynasty (SN: 4/24/99, p. 260), while waddling, cold-blooded ancestors of mammals sloughed off their last reptilian features.

"There are very few places in the world where there is a window on that slice of geologic time," says Andre R. Wyss, a paleontologist at the University of California, Santa Barbara who was a member of the team that excavated the finds.

Among the remains, the researchers identified seven previously unknown species, including four cynodonts, which were the earliest mammal-like reptiles, and one rynchosaur, a parrot-beaked reptile of a group that disappeared shortly after dinosaurs emerged.

Two partial jaws come from goat-size, plant-eating dinosaurs belonging to a group known as prosauropods. Paleontologists view prosauropods as the first dinosaurs to succeed over a wide territory.

The jaw fragments' presence beside rynchosaur remains--plus other indirect evidence--imply an age of about 230 million years, the researchers argue. That figure puts the fossils in the running for the oldest dinosaur find.

Other scientists are disinclined to declare the fossils the winners, however, in the absence of a radiometric date, which is obtainable only when a layer of volcanic ash lies at a fossil's depth.

Prosauropod remains found previously in other parts of the world could be as old as the Madagascar ones, says Hans-Dieter Sues, a paleobiologist at the University of Toronto.

What most excites Wyss, however, is the diversity of Triassic life represented in the new finds, the quality of the specimens, and the enormous potential of the remote, undeveloped site for revealing more. The excavators have combed exposed Triassic strata in just 40 square kilometers on the dry western side of the island. The lightly packed sedimentary rock that held the fossils extends 2,000 km along the rift that formed as Madagascar tore away from Africa.

Typically, Triassic specimens are squashed flat, Wyss says, but the Madagascar fossils are fully three-dimensional. He calls them "to die for."

Only a handful of research teams has excavated Madagascar's sediments. Outside the finds of Wyss and his colleagues, the few fossils recently mined don't date back as far as the Triassic. Wyss predicts that the situation will change: "My guess is this is going to be the Hall of Fame for the late Triassic."