Oldest dinosaur opens a window on Triassic age

Science

They were led to a remote valley amid the dry western grasslands of Madagascar by the journey of a French paleontologist, his tantalizing discovery, and a villager named Mena.

The team of American and local scientists had hoped to uncover the remains of a beaked dinosaur that experts believed might have lived as long as 200 million years ago. What they unearthed beneath the red dirt was a prehistoric menagerie that includes the oldest dinosaur fossils yet found.

The perfectly preserved fossil finds, estimated to be 230 million years old, hold huge promise for illuminating a mysterious time known as the Triassic Period. Indeed, scientists say they may provide clues about how and when the tree of life branched to form dinosaurs, birds, and the furry, opossum-like creatures believed to be the very first mammals.

"What we've got is a piece that has otherwise been missing that documents what appear to be some of the earliest dinosaurs," says J. Michael Parrish, a paleontologist at Northern Illinois University in DeKalb and one of the authors of a paper on the find in today's issue of the journal Science. "We may have a slice of time that hasn't been found anywhere else."

What's perhaps most remarkable about the find is the pristine state of the fossils, which have withstood millions of years.

"We have complete skulls and bodies of animals that were previously only found in very fragmentary materials," says Andre Wyss, a geologist from the University of California at Santa Barbara and a co-author of the paper.

The dinosaurs deemed to be the oldest represent two previously unknown species of prosauropods. They are the predecessors of sauropods, a genus of dinosaurs that millions of years later grew to be the most massive creatures of the era. Analyzing fossilized jawbones, scientists believe the two yet-to-be-named species were vegetarians with long necks and small heads that could walk on two or four legs.

Evidence of transition

An even richer cache of information, however, is represented in the complete skeletons and skulls of eight other creatures found at the site. In these creatures, scientists found evidence of a gradual transition from reptilian to mammalian structures - such as the shift from one bone in the ear to three, as is common in today's mammals.

These changes, particularly in bone-and-jaw structure, are evolutionary signs that help paleontologists fill in missing branches on the evolutionary tree.

"The diversity of the fossils may allow us to greatly clarify who is related to whom and the timing of the origin of mammals," says Dr. Wyss. "It's a fantastic source of information about the evolutionary appearance of the group to which we belong."

Dating dinosaurs and other creatures that far back in time is problematic. Of the four major sites around the world where scientists have found dinosaur remains from the Triassic Period, only one - in Argentina - has the type of mineral sediment rock that allows for accurate radioactive isotope dating.

So rather than rely on such measurements, paleontologists at the Madagascar site examined the cast of characters and tried to determine the age of the fossils by creating the evolutionary equivalent of a team picture.

"If you had some players that were veterans at the end of their career as well as rookies at the beginning of their careers, then there can only be a few years that the pictures can represent," says John Flynn, the paper's lead author and a paleontologist at the Field Museum in Chicago.

How the team of scientists from the US and Madagascar tracked down these fossils is a tale worthy of Indiana Jones.

For most of this century, the island continent off the eastern coast of Africa was off the map as far as ancient fossils were concerned. Madagascar's heavy vegetation made it difficult to find exposed rock valleys, which are the favorite fossil hunting grounds of paleontologists. Also, rural roads were often impassable. Besides, the expense of operating in such an isolated locale was imposing.

But finds in remote parts of world - including Argentina, Brazil, and Morocco - as well as new glues that allowed for easier fossil recovery encouraged paleontologists to explore the fringes of the world. The rise of satellite-positioning systems also helped.

Following French footprints

In 1983, French paleontologist Eric Buffetaut reported finding the fossil remains of a rhynchosaur in west Madagascar. On a quest for more rhynchosaurs, as well as other ancient critters, US and Malagasy scientists slogged to remote villages in 1996 to inquire about buried animal bones.

In one village, they found Mena, who claimed to know about some fossils not far from his village. He led them to a hill of red dirt that turned out to be the treasure trove.

But the treasure that Mena revealed is far from tapped out. Dr. Parrish and the other scientists claim they have a huge backlog of fossils to describe. There are also numerous other promising locations in the back country.

"If the dinosaurs that Flynn and his co-workers discovered are indeed the earliest members of that group, or even close to the earliest, it's crucially important that more complete remains be found," says David Krause of the State University of New York at Stony Brook.

(c) Copyright 1999. The Christian Science Publishing Society