A new Cretaceous dinosaur sheds light on global sauropod evolution
21 October 2016
A new species of dinosaur has been presented in Scientific Reports. Savannasaurus elliottorum is a new genus and species of dinosaur from western Queensland, Australia. The bones come from the Winton Formation, a geological deposit approximately 95 million years old. Uppsala palaeontologist Dr Benjamin Kear, an expert on Australian fossil reptiles, is one of the authors of the study.
Savannasaurus was discovered by David Elliott, co-founder of the Australian Age of Dinosaurs Museum, while mustering sheep in early 2005.
“I was nearly home with the mob—only about a kilometre from the yards—when I spotted a small pile of fossil bone fragments on the ground. I was particularly excited at the time as there were two pieces of a relatively small limb bone and I was hoping it might be a meat-eating theropod dinosaur,” says David Elliott.
He returned to the site later that day to collect the bone fragments with his wife Judy, who ‘clicked’ two pieces together to reveal a complete toe bone from a plant-eating sauropod. The Elliotts marked the site and made arrangements to hold a dig later that year.
The site was excavated in September 2005 by a joint Australian Age of Dinosaurs (AAOD) Museum and Queensland Museum team and 17 pallets of bones encased in rock were recovered. After almost ten years of painstaking work by staff and volunteers at the AAOD Museum, the hard siltstone concretion around the bones was finally removed to reveal one of the most complete sauropod dinosaur skeletons ever found in Australia. More excitingly, it belonged to a completely new type of dinosaur.
In the same publication, Dr Stephen Poropat, lead author of the study (and formerly a post doc at Uppsala University), and colleagues announced the first sauropod skull ever found in Australia. This skull, and the partial skeleton with which it was associated, has been assigned to Diamantinasaurus matildae—a sauropod dinosaur named in 2009 on the basis of its nickname Matilda.
“This new Diamantinasaurus specimen has helped to fill several gaps in our knowledge of this dinosaur’s skeletal anatomy. The braincase in particular has allowed us to refine Diamantinasaurus’ position on the sauropod family tree,” says Stephen Poropat.
He collaborated with British sauropod experts Dr Philip Mannion (Imperial College, London) and Professor Paul Upchurch (University College, London), among others, to work out the position of Savannasaurus (and refine that of Diamantinasaurus) on the sauropod family tree. Both Savannasaurus and Diamantinasaurus belong to a group of sauropods called titanosaurs. This group of sauropods includes the largest land-living animals of all time. The new Diamantinasaurus specimen have helped the researchers to demonstrate that titanosaurs were living worldwide by 100 million years ago.
The researchers behind the study suggest that the arrangement of the continents, and the global climate during the middle part of the Cretaceous Period, enabled titanosaurs to spread worldwide. Australia and South America were connected to Antarctica throughout much of the Cretaceous.
Ninety-five million years ago, at the time that Savannasaurus was alive, global average temperatures were warmer than they are today. However, it was quite cool at the poles at certain times, which seems to have restricted the movement of sauropods at polar latitudes. The researchers suspect that the ancestor of Savannasaurus was from South America, but that it could not and did not enter Australia until approximately 105 million years ago. At this time global average temperatures increased allowing sauropods to traverse landmasses at polar latitudes.
“This pattern of climate-controlled distribution was actually evident in other animals and plants that lived at the same time as Savannasaurus during the mid-Cretaceous in Australia. However, our analysis provides the first compelling evidence that giant herbivorous dinosaurs were subject to these same environmental constraints, and that this signature of periodic trans-polar migration was likely a broader characteristic of Australian faunas and floras from that time,” says Benjamin Kear.
Savannasaurus was a medium-sized titanosaur, approximately half the length of a basketball court, with a long neck and a relatively short tail.
“With hips at least one metre wide and a huge barrel-like ribcage, Savannasaurus is the most rotund sauropod we have found so far—even more so than the somewhat hippopotamus-like Diamantinasaurus. It lived alongside at least two other types of sauropod, Diamantinasaurus and Wintonotitan, as well as other dinosaurs including ornithopods, armoured ankylosaurs, and the carnivorous theropod Australovenator,” says Stephen Poropat.
Find out more:
Poropat et al. (2016) New Australian sauropods shed light on Cretaceous dinosaur palaeobiogeography, Scientific Reports 6, Article number: 34467, doi:10.1038/srep34467