A relative of a giant fish-eating dinosaur that dwarfed T. rex once roamed Australia, say researchers, providing growing evidence for the worldwide distribution of many dinosaur branches.
They add the find provides "weak" evidence to support the theory that Africa was the first of the continents to split from Gondwanaland.
Co-author, Thomas Rich of Museum Victoria, says the claims, published in Biology Letters, are based on a four-centimeter (1.6-inch) neck vertebra found by Michael Cleeland and George Caspar at Dinosaur Cove near Cape Otway, Victoria.
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Rich says the fossil belongs to the group of dinosaurs known as spinosaurs and came from a specimen two to three meters (6.6 to 9.8 feet) long that lived about 105 million years ago in the early Cretaceous period.
Spinosaurs, a fish-eating theropod, are believed to be the biggest of all the predatory dinosaurs -- larger thanTyrannosaurus or Gigantasaurus -- growing up to 17 meters (56 feet) long.
Rich says the fossil was identified by lead author Paul Barrett from the Natural History Museum in London.
Barrett says the Australian vertebra is almost identical to that of the well-known British dinosaur Baryonyx.
"These strong similarities in the general proportions of the vertebra and some of its specialized features led us to make this identification," he says. "Spinosaurid neck vertebrae are very long relative to their height and also have characteristic boney struts that set them apart from other theropod dinosaurs."
However he says the fossil is too limited to give more insight into the Australian version of this dinosaur.
"Although the vertebra is clearly a spinosaurid, there is not enough of the animal preserved to make the detailed comparisons necessary to work out how similar or different it was to the other known members of the group," he says.
"For this reason we decided not to name it, nor did we try to shoe-horn it into any existing genus," he adds. "We hope that future discoveries will tell us much more about the anatomy and relationships of this animal."
Rich says the find gives greater insight into the evolution of the so-called "spine lizards."
He says the presence of a spinosaur in Australia also suggests this group once roamed the globe and were not restricted to a particular region, as previously thought.
"Spinosaurs were previously known to be from Europe, Africa and South America," he says.
"The existence of this neck vertebra is part of an emerging story that [in the Early Cretaceous period] the dinosaurs of Australia were part of a cosmopolitan fauna," says Rich.
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He says this find along with recent discoveries of other dinosaur groups in Australia, also thought to be limited geographically to the northern hemisphere, is further evidence of a worldwide distribution of dinosaur groups.
"The same groups of dinosaurs were widespread when the Earth was once a supercontinent," says Rich. "When the Earth evolved into separate continents, the various families of dinosaurs had already reached those land masses, which explains why the same ones have been found in places now far apart from one another."
Among the dinosaur groups to have been discovered in Australia recently are the neovenatorid, tyrannosaurid and dromaeosaurid theropods.
Rich says it is hard to predict whether further dinosaur groups will be found because although the dinosaur groups known to have been present in Australia has been extended, the fossil record remains quite sparse.
"A third of all the dinosaurs that are found in Australia are represented by one fossil," he says.
"[That means] if seven things hadn't been found our knowledge would have been decreased by 30 percent."
The authors say the results also indicate some support for the "Africa first" theory of Gondwanan fragmentation as a comparison of dinosaur faunas shows greater diversity between Australia and Africa than South America.
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