Paleontologists have found what could be the earliest known dinosaurs, a couple of kangaroo-sized plant eaters that roamed Madagascar about 230 million years ago.
The same site also yielded fossils of the reptile lineage that later evolved into mammals.
Researchers from the Field Museum in Chicago, Northern Illinois University, University of California at Santa Barbara, and Universite d’Antananarivo in Madagascar collected the fossils during four separate expeditions between 1996 and 1999.
The findings are reported in the Oct. 21 issue of the journal Science.
The Madagascar fossils will be on display at the Field Museum Oct. 22 through Jan. 2, 2000.
A Revolution in Evolution
“It’s a whole new window in the evolution of animals at a key point,” comments Neil Shubin, a University of Pennsylvania biology professor.
With a relatively sparse fossil record, “Madagascar has always been something of an enigma,” Shubin says. “They’re filling both a gap in time and a gap in space. We see the transition from an archaic fauna of reptiles and amphibians to a more modern fauna. You think about it, these are creatures that were going to be around for millions of years. It’s a revolution in the history of life that happened during this time period.”
Madagascar is an island off east Africa, but 230 million years ago, it and all of Earth’s continents were joined as the supercontinent Pangea.
This period known as the Triassic marked the appearance of many modern groups of animals, including mammals, crocodiles, turtles, frogs and bony fish.
The most noteworthy newcomers were, of course, the dinosaurs, destined to dominate the landscapes for the next 165 million years.
Their beginnings appear to have been humble.
So far, the Madagascar site has yielded only the jaws and partial skull fragments of two early dinosaurs. The shape of the bones indicate the animals were of a group of dinosaurs known as prosauropods.
“This animal is probably the size of a small kangaroo,” says John Flynn, curator and chair of the department of geology at the Field Museum in Chicago and lead author of the Science paper. “They probably would have ambled about on four legs. It’s sort of like the way kangaroos walk around when they’re feeding.”
The region back then was wetter, he says. “It was even more sort of tropical. There were big rivers running through this area. I would imagine it being something like the Mississippi river valley.”
Although small, prosauropods later evolved into behemoth sauropod dinosaurs such as Apatosaurus and Brachiasaurus.
None of the new species has been officially named yet but geologist Andrew Wyss of the University of California at Santa Barbara, who worked on the study, said some of the names would honor local residents who found the fossil bed.
“A boy said that his older brother had found some bones,” Wyss said in a statement. “So we waited around a half day for the brother, Mena, and sure enough, he showed us a hill with a mound of them.”
The Madagascar rocks in which the fossils were found don’t contain minerals that can be dated directly. Rather, Flynn and his colleagues argue their rocks are very old based on what else is and isn’t found there.