University researchers discover Australia's oldest amphibians
University researchers discover Australia's oldest amphibians
Two Brisbane children have helped Australian researchers discover some of the world's oldest fossil amphibians in Central Queensland, including amphibians not previously found outside the northern hemisphere.
The fossils are the first Australian evidence of how and why fishes first crawled onto land 350 million years ago, leading to the emergence of amphibians and modern reptiles, birds and mammals.
The findings form the subject of a paper published this month (June 27) in prestigious British scientific journal, Nature. It was written by Dr Tony Thulborn, a reader in the University of Queensland's Zoology Department in collaboration with University of Queensland PhD student Mr Tim Hamley, Dr Susan Turner of Queensland Museum and Dr Anne Warren of La Trobe University, Victoria.
Guy Thulborn, 9 and Angus Hamley, 13, were on a trip west of Rockhampton last year with their fathers, vertebrate palaeontologists Dr Thulborn and Mr Hamley, when Dr Thulborn found what he thought was part of an ancient fish jaw.
He showed it to Guy, asked him to look for similar teeth, and Guy promptly found another piece of the same animal - but with the unmistakable features of an amphibian, not a fish. Tim Hamley and Angus collected fragments assumed to be fish, but later found to include amphibian pieces.
Dr Thulborn said palaeontologists had assumed that the breakthrough from water to land-based animals occurred in Euramerica, because the earliest fossil amphibians had been found there, particularly in Scotland and North America.
"Now, to everyone's surprise, we've found these creatures on the far side of the planet, in eastern Gondwana," he said.
"This discovery means that the earliest amphibians weren't confined to Euramerica: they had a worldwide distribution in equatorial regions. It also means that the great breakthrough onto land is just as likely to have occurred in Australia, as in Europe or North America.
"The amphibians we've found are some of the earliest known. And we've found not just several different sorts of amphibians, but their entire ecological context - an ancient fossil community, with freshwater fishes, invertebrates and plants. "
During a second trip to the Central Queensland site in April, the four researchers found evidence for at least three types of extinct amphibians - two of them distantly related to modern living amphibians, and the third representing the ancestry of reptiles, birds and mammals.
The fossils are estimated to be about 333 million years old, and from the early Carboniferous period - at least twice as old as the earliest-known dinosaurs. The researchers have yet to determine how many amphibian species might be present at the site, having pinned down identifications only to the level of major groups.
The creatures, which may have resembled modern salamanders, lived in swamps, lakes and rivers at a time when Australia was joined to India, Africa, Antarctica and South America in a giant continent called Gondwana. Initially Gondwana and the European-American continent known as Euramerica, were separate.
Dr Thulborn said the fauna found in the remote central Queensland site were remarkably similar to known Euramerican fauna of the same early Carboniferous age.
"This immense geographic range implies that the north-western margin of Gondwana may have approached or collided with the southern margin of Euramerica, opening a route for vertebrates to disperse across continents," he said.
Dr Thulborn said during the early Carboniferous period, it was believed the whole of Gondwana drifted north to meet southern Euramerica. Only later did Gondwana drift free again and began breaking up into separate continents.
"It's been assumed that Gondwana was separated from Euramerica by an ocean barrier, and that these two landmasses didn't collide until quite late in the Palaeozoic era. Then, of course, following conventional wisdom, the amphibians and freshwater fishes of Euramerica could have spread into Gondwana," he said.
"Our discovery reveals that there must have been a faunal exchange route between Euramerica and Gondwana by the early Carboniferous (somewhat earlier than usually supposed). It's conceivable that some faunal exchanges went in the opposite direction - from Gondwana into Euramerica.
"Much of our conventional thinking about amphibian origins has been turned upside down and given a thorough shaking-out. It's no longer a scientific question focussed on Euramerica; it has suddenly blown out into a scientific question of global proportions."
The latest finding of amphibians was made in ancient mudstone deposits of the Drummond Basin, west of Rockhampton, along with abundant remains of freshwater fishes including lungfish and sharks.
The researchers collected several boxes of materials from the site, which they regard as one of the world's most significant for investigating the history of early freshwater fishes and amphibians.
The site lies in an uninterrupted sequence of sedimentary layers extending back through the Carboniferous period (360 million-289 million years ago) and into the Devonian (400 million-360 million years ago). This means there is a fair chance of finding even older fishes and amphibians in underlying rock layers.
Dr Thulborn said fossil bones at the site were perfectly preserved in three dimensions, unlike crushed and distorted fossils from early Carboniferous sites overseas, providing unambiguous information on the detailed anatomy, which is essential for studies of evolutionary change.
Detailed studies of the newly-discovered fossils are being continued by Dr Turner, an expert in fish of the Devonian and Carboniferous periods, and Dr Warren, a specialist in extinct amphibians.
Maurizio Bigazzi, a taxidermist and model-maker in the University of Queensland's Zoology Department, formerly of the University of Bologna, has created three-dimensional life-sized models of the amphibians, basing his restorations on North American and European animals known from complete fossil skeletons.
The models will be on display at Queensland Museum following publication of the Nature article, along with original fossil specimens and casts.
For further information, contact Dr Thulborn, telephone 07 3365 2656 or Mr Hamley, telephone 07 3365 4825.
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