A new species of giant long-necked dinosaur revealed today sheds light on the likely origin of Australian sauropods.
The creature was called Savannasaurus elliottorum after grazier David Elliott, chairman of the Australian Age of Dinosaurs Museum (AAOD) in Winton, Queensland, who first found the fossil bones in the area during a sheep muster in 2005.
While the discovery site was excavated in September of that year by a team from the AAOD and Queensland Museum, it has taken the decade since to remove the bones from the rocks in which they were encased.
Savannasaurus belonged to a branch of sauropods known as titanosaurs, the largest land animals ever to have lived, said Dr Stephen Poropat of the AAOD Museum, who is lead author of a paper describing the findings in today's Scientific Reports.
He said only about 20 to 25 per cent of Savannasaurus' skeleton had been recovered with most of the torso, front limbs and pelvis intact.
"Because they are very large animals it would take a fair bit of sediment to bury it before predators come along," Dr Poropat said.
He said a tooth of a carnivorous dinosaur had been found at the fossil site, which suggested there had been some scavenging on the remains.
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Dr Poropat said Savannasaurus would have been a medium-sized titanosaur about half the length of Diplodocus, measuring between 12 to 15 meters in length, with a long neck and relatively short tail.
However, he said its most distinctive feature was its hip width, which measured up to 1.5 meters.
Dr Poropat and colleagues also described another dinosaur, Diamantinasaurus matildae, first discovered in 2009, whose skeleton includes the first sauropod skull found in Australia.
Savannsaurus and the new Diamantinasaurus specimen shed light on a debate over the origin of Australian titanosaurs.
Previous studies of Australia's megafauna have suggested they were most similar to dinosaurs from Laurasia - the ancient continental mass in the Northern Hemisphere.
But Dr Poropat said this had never really made sense given the two super continents of Gondwana and Laurasia were separated.
He said the new study showed Savannasaurus and Diamantinasaurus were in fact more closely related to species from South America.
"But as the South American fossil record has improved and the Australian fossil record continues to grow, we are getting a better understanding of how close our dinosaurs were to those from South America."
Dr Poropat said it appeared Savannasaurus came to Australia around 105 million years ago from South America.
He said it appeared as if these titanosaurs took advantage of the warmer global temperatures at the time to disperse from South America through Antarctica to Australia at a time when all three continents were connected.
Dr Adam Yates, senior curator of earth sciences at the Northern Territory Museum, said he believed the paper's findings were valid.
Titanosaurs in particular represented one of the "last grey areas" of understanding in the dinosaur story.
"They are abundant and found all over the world, but their remains are often very incomplete, and as a consequence our understanding of the interrelationship of different titanosaurs is quite puzzling and we don't have a good family tree worked out yet," he said.
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Dr Yates said the movement of the titanosaurs from South America made a "lot of sense".
The titanosaurs were a relatively young group of dinosaurs and did not start dispersing until the Cretaceous.
"By that time the only terrestrial route into Australia was via Antarctica," Dr Yates said.
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