Two fossil titanosaurs, a group of sauropod dinosaurs known for the enormous size of some species, have caused paleontologists to rethink the climatic history of the Cretaceous. The discoveries confirm the existence of these giant beasts in western Queensland in the late Cretaceous, and suggest there was probably a period of unusual warmth in Antarctica, which allowed their ancestors to migrate across the continent.
Dr Stephen Poropat of the Australian Age of Dinosaurs Museum has revealed two sauropod specimens found near Winton, Queensland in a study published in the journal Scientific Reports. One of these, Savannasaurus elliottorum, is described for the first time in the paper.
One previous Diamantinasaurus matildae specimen has been described before, but the fossil Dr Poropat describes is the first time we have seen part of the cranium, not just of this species, but of any Australia sauropod. Both are 90 to 100 million years old.
Outline of a Diamantinasaurus matildae with the bones found for the newly described specimen shown. Travis Tischler / © Australian Age of Dinosaurs Museum of Natural History
As interesting as the two are to dinosaur enthusiasts, their location and relationship to other giant herbivores may be more important.
“There is no evidence of titanosaurs in Australia more than 105 million years ago,” Poropat told IFLScience.
Some sauropod species, members of the titanosauriforms of which titanosaurs were prominent examples, were present, but the species covered in the paper appear far too closely related to South American titanosaurs to have evolved independently.
Instead, Poropat and his co-authors conclude they reached Australia during the late Albian stage, which ended 100 million years ago. By that time Africa and India had detached themselves from the remnants of Gondwanaland. Barring some improbable cross-oceanic swimming, there was only one way for these giant beasts to have reached Australasia.
For most of the Cretaceous era Australia and South America were joined to Antarctica. Although Antarctica was not icebound as it is today, it was cold enough to form a barrier, rather than a bridge, between the other two continents. Fossils are hard to come by from central Antarctica so paleontologists are seeking clues to how permeable that barrier was, and therefore how stable the climate may have been, from remnants found on either side.
A titanosaur migration, Poropat told IFLScience, is important because it would indicate Antarctica served as a bridge for much longer than has previously been realized, although marsupials and turtles are known to have used a similar path 50 million years ago.
It would also suggest there may have been a period where global temperatures were above even the general Cretaceous warmth. The paper notes that sauropods were less diverse at high latitudes, suggesting they preferred the warmth.
The world in the Albion era with known titanosaur locations, and a possible route from South America to Queensland. Poropat et al/Scientific Reports
By the standards of almost any other sort of animal, the individuals described in the paper were truly massive. Poropat estimates Savanassaurus was 12 to 15 meters long (40 to 50 feet) and weighing 15 to 20 tonnes (16.5 to 22 tons). Although the Diamantinasaurus described in the paper was smaller, the authors think it was not fully grown. The one previous Diamantinasaurus specimen was 15 to 16 meters (50 to 53 feet) long and probably weighed 23 tonnes (25 tons), or three large African elephants.
Despite this, Poropat says these were “at the smaller end of the [titanosaur] spectrum.” Their relatives include Argentinosaurus, which at 96 tonnes (106 tons) may have been the heaviest species to ever walk on land.