Fossil bones discovered almost 80 years apart in a remote area of Queensland are helping to reveal the shape of a dinosaur that roamed Earth more than 100 million years ago.
We still have only a few fragments — mostly vertebrae and a few ribs — but we now know that Austrosaurus mckillopi was a sauropod, a plant-eating dinosaur with a long neck that walked on four legs.
Sauropods are fairly commonly found in outback Queensland, but the majority of them lived between five million and ten million years after Austrosaurus. This means that Austrosaurus could potentially be their close relative, or even their direct ancestor.
Unfortunately, the bones of Austrosaurus are too incomplete and poorly preserved for us to be able to determine this. But we can tell that Austrosaurus was at least distantly related to other Queensland sauropods, such as Diamantinasaurus and Savannasaurus, since it shares some features with them.
Details of the new research on Austrosaurus were published today in Alcheringa, an Australasian Journal of Palaeontology, and the story of how the fossil bones were discovered is as fascinating as the discovery itself.
The original find
Many amazing fossil discoveries in outback Queensland have been made by people who make their living off the land. As an example, the recently discovered specimen nicknamed “Judy”, which appears to be the most complete sauropod dinosaur ever found in Australia, was discovered by Winton grazier Bob Elliott while he was mustering sheep.
Back in 1932 it was Henry Burgoyne Wade, overseer of the Clutha sheep station northwest of Richmond, who spotted some unusual rocks in one of the paddocks.
Realising they were fossils, he showed them to station manager Harley John McKillop, who contacted his Brisbane-based brother, Dr Martin Joseph McKillop.
Dr McKillop travelled more than 1,700km to Clutha to help collect more bones and then sent a sketch of one to Heber Longman, director of the Queensland Museum in Brisbane. Longman instantly recognised the significance of the find and asked for the fossils to be sent to him.
The Clutha fossils arrived in Brisbane in January 1933 and within two months Longman realised they were backbones from a long-necked sauropod dinosaur. He named the new dinosaur Austrosaurus mckillopi (“Dr McKillop’s southern reptile”) and estimated its length as 15 metres.
Austrosaurus would have been a land-living animal but Longman realised that its bones had been buried at the bottom of the Eromanga Sea. This inland sea covered much of western Queensland 102 million years ago.
Because it was buried at the bottom of an inland sea, it is possible that the carcass of Austrosaurus mckillopi was scavenged as it sank by sharks and marine reptiles like the huge pliosaur Kronosaurus. Artwork by Travis R Tischler, Author provided
A lost dig site
After 1933, relatively little attention was paid to Austrosaurus. In the 1970s, palaeontologists tried to relocate the site from which the bones were exhumed, but these attempts failed. Consequently, the site was considered lost.
In 2011, I started work as a postdoctoral researcher at Uppsala University in Sweden. The focus of my research was Australia’s Cretaceous sauropods, and Austrosaurus intrigued me.
The original Austrosaurus mckillopi backbones viewed from the left side. Stephen Poropat, Author provided
Most of the preserved bones were vertebrae from the chest region, but some fragments looked like bits of rib. One thing was particularly curious: on several fossil blocks, the back half of one vertebra was positioned immediately before the front half of another vertebra, with very little rock in between.
The bones of Austrosaurus must have been preserved in sequence, close to life position, which suggested that more of Austrosaurus was waiting to be found.
In 2014 I contacted Dr Tim Holland, then curator at Kronosaurus Korner museum in Richmond, about relocating the site. I had worked out the approximate location of the site by overlaying Longman’s 1933 map — complete with an “X” to mark the spot — on Google Earth.
Thanks to David and Judy Elliott, cofounders of the Australian Age of Dinosaurs museum in Winton, I also knew that Wade and the McKillops had erected a sign, supported by two wooden posts, at the Austrosaurus site in 1933.
A photograph of the sign which once marked the Austrosaurus mckillopi dig site. Courtesy of Richard Wade, Author provided
To relocate the Austrosaurus site, Tim enlisted the help of Richmond mayor John Wharton, who had grown up on Clutha and knew about the wooden posts. By 2014 both posts had fallen over and a ground-based search for them among the dried Mitchell grass was unsuccessful.
Unperturbed, John jumped in his helicopter and soon spotted the posts from the air. Once he landed, he saw some rocks nearby and they contained fragments of sauropod bone. John had rediscovered the Austrosaurus site!
Back to the dig site
Shortly after I received the good news from him, Tim started planning a trip to the site. We visited twice in 2014 and although we found plenty of bone fragments we struggled to get through the clay-rich topsoil.
A backhoe helps at the Austrosaurus mckillopi dig. Stephen Poropat, Author provided
In 2015, Tim organised another dig, and Richmond Shire Council loaned their backhoe to remove the soil. Together with a team of dedicated volunteers, we recovered six deeply buried ribs, surrounded by fossilised marine bivalves (relatives of modern day clams and mussels).
The spacing between the ribs showed that they were close to life position, just like the vertebrae. We were delighted that more than 80 years after the initial discovery of Austrosaurus we had found more of the same individual.
From 2014 to 2016, for a few days each year, I studied the original bones of Austrosaurus in Brisbane with Jay Nair, a PhD candidate at The University of Queensland.
Together, we worked out the sequence of Austrosaurus’ vertebrae. When we scaled photos of the complete series with photos of the ribs found in 2014–15, we confirmed that they belonged to the same animal.
In 2016, another PhD candidate at The University of Queensland, Caitlin Syme, tried to work out how Austrosaurus‘ carcass came to rest at the bottom of the Eromanga Sea.
She concluded that for a portion of the carcass to have remained intact, some of the soft tissue must still have been in place when it sank. This suggests that at least this portion of the carcass was not “picked clean” by scavengers before it sank. Why that is, we might never know.
The reconstructed Austrosaurus mckillopi site. The backbones (top) were excavated in the 1930s, and the ribs (projecting down) were dug up in 2014 and 2015. Stephen Poropat, Author provided
Much still to learn about Austrosaurus
Even though my colleagues and I have enhanced the original and only known specimen of Austrosaurus, we still don’t know that much about its anatomy or appearance.
We can tell that Austrosaurus is a type of sauropod called a somphospondylan titanosauriform — this means that it sits on a branch between brachiosaurs like Giraffatitan, and titanosaurs like Savannasaurus and Diamantinasaurus, on the sauropod family tree.
Placing it more precisely than that, however, is tough. On the plus side, we have been able to identify features of Austrosaurus that distinguish it from all other sauropods.
One of the best ways to advance palaeontological understanding is to find new fossils. Another is to rigorously reassess old specimens. By conducting the Austrosaurus project, my colleagues and I did both.
Although we ended up with a less-than-amazing specimen and an incomplete story, we hope it will inspire other people to revisit old sites while continuing the search for new ones. It is tantalising to wonder what else might be waiting to be found in outback Queensland.
Written by Stephen Poropat, Postdoctoral Researcher (Palaeontology), Swinburne University of Technology. This article was originally published on The Conversation. Read the original article.