World's oldest dinosaurs
Jawbones from two dinosaurs found in Madagascar are likely to be the oldest ever discovered, and the site promises further fossil wealth from the little understood late Triassic period.
The find, published in the latest issue of Science by a team of palaeontologists from the US and Madagascar, includes fragmentary remains of two plant eating prosauropods, along with the remains of eight other prehistoric animals. According to the researchers, this could be just the tip of a much larger fossil iceberg at the same location.
"A wealth of bones is pouring out of our quarries. Once these get cleaned up, we have no doubt that we'll know a great deal more about all of these animals, plus many others. There should be meat-eating dinosaurs present, as well as a host of other novel animals," said Andre Wyss, associate professor of geology at the University of California, Santa Barbara, and co-leader of the research team.
To establish the relative ages, scientists must look to what other kinds of fossils are found in association with the dinosaurs. Of the various early dinosaur sites known worldwide, it has been possible to directly date, by radioisotopic means, only one of them, the one from Argentina, which is roughly 227 million years old. "Our Malagasy fauna and its dinosaurs are possibly as much as 5 million years older, but all that we can say at this point is that all indications point to its being distinctly older than 227," he said.
The fossils are from a period that has long been a puzzle for palaeontologists, the Middle to Late Triassic (225 to 230 million years ago). At the opening of this period, a variety of reptiles, amphibians, and other vertebrates populated the land. By its close, early dinosaurs and mammals had appeared, but a sparse fossil record has left scientists with few clues about what happened in between.
The prosauropods, herbivores about the size of a new-born calf with small heads and long necks, could walk on two or four legs. These primitive dinosaurs either shared a common ancestor with, or were themselves ancestors to, the mighty sauropod dinosaurs that evolved later such as Apatosaurus.
The five pre-mammalian animals that the researchers discovered could also shed light on the origins of the first true mammals. For example, how large, cold-blooded 'mammal-like' reptiles evolved into small warm blooded mammals.