Post by Boomer Chick on Aug 2, 2004 22:41:26 GMT -5
www.theage.com.au/articles/2004/08/01/1091298572627.html?oneclick=true
Long-lost creatures
Scientists worldwide are focusing on a beach in Gippsland to uncover the age-old mystery of mammals, writes science reporter Stephen Cauchi.
One hundred and fifteen million years ago, what is now the coast of Gippsland stretched kilometres inland. There were no flowers or grass, only ferns and conifers. Australia, then much closer to the South Pole, was freezing and dark for months on end.
Dinosaurs roamed the landscape but, scurrying through the undergrowth, were their eventual usurpers: the mammals. But what kind of primitive mammals lived in ancient Gippsland? Residents of Inverloch may well feel flattered, because that's what paleontologists the world over would like to know. Understanding the origins of all modern mammals, from hedgehogs to humans, depends on it.
With recent fossil finds at a Gippsland beach near Inverloch called Flat Rocks, as well as DNA studies, the debate is as fierce as ever. And paleontologists are split over this issue.
The traditional view that placentals and marsupials arose in Laurasia (North America, Europe and Asia) originated from the 19th-century English biologist Russell Wallace. It was a view that was widely held until March 8, 1997, when paleontologist Tom Rich of Museum Victoria and Monash University — and one of Australia's leading discoverers of dinosaur fossils — discovered a 115-million-year old mammal jaw at a coastal fossil site at Flat Rocks.
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In a statement that rocked the world of paleontology, Rich claimed the fingernailsized jaw was not just from a mammal, but a placental mammal — which was thought to have never existed in Australia. It was dubbed Ausktribosphenos nyktos. And if Rich was correct, the traditional theory of Laurasian origin for placental mammals was wrong. Either they arose in Gondwanaland (Australia, Antarctica, South America, Africa and India) and spread to Laurasia to the north — the socalled Garden of Eden theory — or they independently arose on both.
"It was then that we started finding things that looked like placental mammals in the southern hemisphere," Rich says. "This is what got us thinking, well, maybe we can't say they originated on the northern hemisphere."
Now, with the recent Gippsland finds — and in other former Gondwanaland territories such as Madagascar and Argentina — even some traditionalists acknowledge the importance of Rich's work.
Richard Cifelli, a curator at the Oklahoma Museum of Natural History in the US, recently told the international science magazine Discover that Rich's new fossils finds were "fantastically important".
"They're going to rewrite our interpretation of mammalian history. We're just not sure what that interpretation is going to be yet".
Thirty mammal jaws have been uncovered at Flat Rocks since 1997, most about one or two centimetres long. Their teeth are not simply the pointed cones of a reptile; they feature mammalian trademarks such as interlocking upper and lower molars.
But are they the molars of a placental? Rich thinks so. The jawbones have three molars and a premolar. Marsupials have four molars.
"Everyone is convinced they're mammals. At first there was the suggestion that they weren't even mammals," Rich says. "But I think the whole thing was the prejudice that things had to originate in the northern hemisphere."
He admits, however, that "most people don't accept that this thing that we found down at Flat Rocks is a placental mammal".
However, other evidence that placentals evolved in Gondwanaland came in 2001, when an Argentinian team found a 160- million-year-old mammal jaw. And, in 1999, an American team found a 170- million-year-old jaw in Madagascar that looked like it came from a placental. Then there’s studies of placental mammals, such as elephants and sloths, found in South America and Africa that DNA evidence suggests had ancestors living in Gondwanaland well before it joined with Laurasia 80 million years ago.
But how does that explain the raft of fossil evidence pointing to placentals, not to mention marsupials, living in Laurasia well before 80 million years ago? Well, say proponents of the Garden of Eden theory, Gondwanaland was fracturing as far back as 150 million years ago. Continental drift was pushing bits of the supercontinent north, until they docked with Laurasia. Placental mammals may have been carried on these fragments.
The bottom line is, says Rich, better fossil evidence is needed — in particular, not just jaws, the toughest part of the skeleton, but skulls. But while Flat Rocks is now a beach, 115 million years ago it was a river valley — one not conducive to maintaining fossils.
"The bones accumulated in the bottom of a small stream . . . they banged along the bottom there and so any skull would have bounced to pieces, whereas the jaws survived," Rich says. "So that's why we've got jaws and not skulls.
"We need skulls to resolve this issue. Everyone's stated their positions and that's where they're going to stay until we find some new evidence. That's really up to us."
Long-lost creatures
Scientists worldwide are focusing on a beach in Gippsland to uncover the age-old mystery of mammals, writes science reporter Stephen Cauchi.
One hundred and fifteen million years ago, what is now the coast of Gippsland stretched kilometres inland. There were no flowers or grass, only ferns and conifers. Australia, then much closer to the South Pole, was freezing and dark for months on end.
Dinosaurs roamed the landscape but, scurrying through the undergrowth, were their eventual usurpers: the mammals. But what kind of primitive mammals lived in ancient Gippsland? Residents of Inverloch may well feel flattered, because that's what paleontologists the world over would like to know. Understanding the origins of all modern mammals, from hedgehogs to humans, depends on it.
With recent fossil finds at a Gippsland beach near Inverloch called Flat Rocks, as well as DNA studies, the debate is as fierce as ever. And paleontologists are split over this issue.
The traditional view that placentals and marsupials arose in Laurasia (North America, Europe and Asia) originated from the 19th-century English biologist Russell Wallace. It was a view that was widely held until March 8, 1997, when paleontologist Tom Rich of Museum Victoria and Monash University — and one of Australia's leading discoverers of dinosaur fossils — discovered a 115-million-year old mammal jaw at a coastal fossil site at Flat Rocks.
Advertisement
Advertisement
In a statement that rocked the world of paleontology, Rich claimed the fingernailsized jaw was not just from a mammal, but a placental mammal — which was thought to have never existed in Australia. It was dubbed Ausktribosphenos nyktos. And if Rich was correct, the traditional theory of Laurasian origin for placental mammals was wrong. Either they arose in Gondwanaland (Australia, Antarctica, South America, Africa and India) and spread to Laurasia to the north — the socalled Garden of Eden theory — or they independently arose on both.
"It was then that we started finding things that looked like placental mammals in the southern hemisphere," Rich says. "This is what got us thinking, well, maybe we can't say they originated on the northern hemisphere."
Now, with the recent Gippsland finds — and in other former Gondwanaland territories such as Madagascar and Argentina — even some traditionalists acknowledge the importance of Rich's work.
Richard Cifelli, a curator at the Oklahoma Museum of Natural History in the US, recently told the international science magazine Discover that Rich's new fossils finds were "fantastically important".
"They're going to rewrite our interpretation of mammalian history. We're just not sure what that interpretation is going to be yet".
Thirty mammal jaws have been uncovered at Flat Rocks since 1997, most about one or two centimetres long. Their teeth are not simply the pointed cones of a reptile; they feature mammalian trademarks such as interlocking upper and lower molars.
But are they the molars of a placental? Rich thinks so. The jawbones have three molars and a premolar. Marsupials have four molars.
"Everyone is convinced they're mammals. At first there was the suggestion that they weren't even mammals," Rich says. "But I think the whole thing was the prejudice that things had to originate in the northern hemisphere."
He admits, however, that "most people don't accept that this thing that we found down at Flat Rocks is a placental mammal".
However, other evidence that placentals evolved in Gondwanaland came in 2001, when an Argentinian team found a 160- million-year-old mammal jaw. And, in 1999, an American team found a 170- million-year-old jaw in Madagascar that looked like it came from a placental. Then there’s studies of placental mammals, such as elephants and sloths, found in South America and Africa that DNA evidence suggests had ancestors living in Gondwanaland well before it joined with Laurasia 80 million years ago.
But how does that explain the raft of fossil evidence pointing to placentals, not to mention marsupials, living in Laurasia well before 80 million years ago? Well, say proponents of the Garden of Eden theory, Gondwanaland was fracturing as far back as 150 million years ago. Continental drift was pushing bits of the supercontinent north, until they docked with Laurasia. Placental mammals may have been carried on these fragments.
The bottom line is, says Rich, better fossil evidence is needed — in particular, not just jaws, the toughest part of the skeleton, but skulls. But while Flat Rocks is now a beach, 115 million years ago it was a river valley — one not conducive to maintaining fossils.
"The bones accumulated in the bottom of a small stream . . . they banged along the bottom there and so any skull would have bounced to pieces, whereas the jaws survived," Rich says. "So that's why we've got jaws and not skulls.
"We need skulls to resolve this issue. Everyone's stated their positions and that's where they're going to stay until we find some new evidence. That's really up to us."
