95m-year-old Savannasaurus elliottorum leads researchers to propose new theory of how sauropods spread around the world
A new species of giant herbivorous dinosaur has been found in outback Australia, helping to rewrite the textbooks on how the gentle giants spread around the globe.
The species is a member of the group of dinosaurs known as sauropods – such as the brontosaurus, which have long necks and four thick, pillar-like legs. It belongs to a subgroup called “titanosaurs”, thought to have evolved in South America.
Named Savannasaurus elliottorum after the savannah landscape it was found in, and David Elliott, who discovered the bones on his sheep station in central Queensland, its 40-or-so fossilised bones make up one of the most complete sauropod skeletons found to date in Australia.
The species was reported on Thursday in the journal Scientific Reports alongside a specimen of another similar but previously described species, known as Diamantinasaurus matildae.
Together, the two specimens led researchers to redescribe the evolutionary tree of sauropods, and propose a new theory of how they spread across the ancient megacontinent of Gondwana, which joined Australia, Africa, Antarctica and South America.
The 95m-year-old savannasaurus specimen, nicknamed Wade, was found by Elliott, who runs the Australian Age of Dinosaurs museum on his farm near Winton. It documents a series of other dinosaur discoveries dating back nearly 20 years.
“I was mustering sheep for crutching,” Elliott said. “It was in 2006 and I found a little toe bone. I thought it was a theropod dinosaur, actually – it looked like a bit of a limb bone. I was really excited about it. It turned out to be a sauropod.”
Elliot’s wife, Judy, looked at two parts of the bone and saw they fitted together, revealing it was a single complete toe of a sauropod, rather than two different parts of a theropod toe.
Over the following years, the Elliott family, scientists and volunteers excavated 17 pallets’ worth of fossil fragments, reconstructing about 20% of a complete skeleton. The dinosaur was found to be between 12 and 15 metres long.
About the same time, Elliott discovered part of another sauropod skeleton, which turned out to be a specimen of a species called Diamantinasaurus matildae. The find included the only skull of that species ever seen.
The two discoveries helped the researchers redraw the evolutionary tree of related dinosaurs, helping them to reconstruct their movement around the world.
“The more anatomical information you can derive from a specimen, the more accurately you can place it on the dinosaur family tree,” said Stephen Poropat, a paleontologist who works with the Australian Age of Dinosaurs museum.
With the new information, Poropat and colleagues found the diamantinasaurus was a less advanced member of the family than previously thought. The new savannasaurus was also to found to be a primitive member of the group.
The evolutionary analysis, which compared the specimens with similar ones in South America, meant there was a small window between 100m and 105m years ago when an ancestor of the two dinosaurs must have crossed over land from South America, through Antarctica, to Australia.
While the evolutionary analysis suggested the dinosaurs only made the journey about 100m years ago, the position of the continents at the time showed it should have been possible earlier.
“We realised there must have been some sort of barrier to them dispersing between South America and Australia before about 105m years ago,” Poropat said.
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The researchers argued the cool climate of the polar region could have been that barrier. And a period of global warming that occurred about 105m years ago could have made the polar region more suitable to the dinosaurs. “Whether by accident or by choice, some of them found themselves in Australia,” said Poropat.
John Long, a paleontologist from Flinders University in Australia who wasn’t involved in the research, said the find was amazing.
“The Winton formation keeps yielding this amazing material and it’s showing such a great diversity of titanosaurs that were around in Australia in this middle cretaceous period,” Long said.
He said it was previously thought that most Australian dinosaurs travelled south from Asia. “It’s now emerging that most of our dinosaurs have a South American affinity,” he said.
The researchers’ theory about climate change allowing the dinosaurs to spread was interesting and “fair enough”. “It’s only putting an idea out there that needs more evidence.”
Long said if the theory were correct, it could be confirmed by other finds.
“Based on that, we could make the prediction that we would find more exciting dinosaurs that occur in South America. Like, for example, the horned carnotaurus – it’s a theropod meat-eating dinosaur with horns on its head.”
Source: The Guardian