Editors note: we can now confirm that one of the footprints found is the largest ever discovered.
The thousands of dinosaur footprints found at Walmadany in Australia's Kimberley region come from at least 21 Cretaceous species, a comprehensive study has revealed. Some of these, at 1.7 meters (5.6 feet) long, are candidates for the largest footprints every found. The collection is unparalleled in the world in diversity recorded at a single site, making it a good thing that plans to destroy the location forever were defeated by one of the country's largest environmental campaigns.
In 2008 the Western Australian government chose Walmadany (also known as James Price Point) as the preferred location to process natural gas from the vast fields off the coast of northwest Australia, despite the existence of cheaper and less environmentally sensitive alternatives.
The decision sparked a huge campaign to protect the site, with the giant dinosaur footprints being highlighted as one reason the area needed to be saved. The Goolarbooloo people, Walmadany's traditional custodians, contacted Dr Steve Salisbury of the University of Queensland to document the prints and reveal as much as possible about the extinct creatures that created them.
“It is extremely significant, forming the primary record of non-avian dinosaurs in the western half the continent and providing the only glimpse of Australia’s dinosaur fauna during the first half of the Early Cretaceous Period,” Dr Salisbury said in a statement. “It’s such a magical place –Australia’s own Jurassic Park, in a spectacular wilderness setting.”
Walmadany aside, Australia's dinosaur record is almost exclusively from the east coast, and millions of years younger than these footprints. Consequently, Salisbury's work provides almost the only window we have into the ecosystem that existed in the Western Australia 127-140 million years ago.
Dr Anthony Romilio and Linda Pollard creating a silicon cast of sauropod tracks in the Walmadany sandstone. Steven W. Salisbury.
Footprints from the medium-sized theropod Megalosauropus broomensis were described in the 1960s, but the Goolarbooloo people have known of the tracks for tens of thousands of years, ascribing them to Marala, the emu-man, who gave them their laws. More recent efforts described nine new types of tracks, subsequently increased to sixteen, but these lacked detail. The biggest footprints were missed initially – seen as too large to come from an animal.
Salisbury, on the other hand, has published a very long account of his findings in the Journal of Vertebrate Paleontology.
The knowledge did not come easy. Salisbury told IFLScience: “There are probably a lot of tracks under water right now, and others buried under dunes. At the moment the only stretch where rocks are exposed is in the intertidal zone.” Consequently, the team had to hurriedly map and take casts of the prints before the region's giant tides come flooding back. Salisbury said he and his fellow researchers frequently got so caught up in their work they had to wade back to shore with their equipment held above their heads. On one occasion they looked back to see an enormous crocodile cruising the waters they had just left.
The results were more than worth it, however. “There were five different types of predatory dinosaur tracks, at least six types of tracks from long-necked herbivorous sauropods, four types of tracks from two-legged herbivorous ornithopods, and six types of tracks from armored dinosaurs,” Salisbury said in a statement.
“Among the tracks is the only confirmed evidence for stegosaurs in Australia. There are also some of the largest dinosaur tracks ever recorded. Some of the sauropod tracks are around 1.7 meters long.”
Some of the thyreophoran prints found at Walmadany with silhouettes of the animals that might have made them. Salisbury et al/Anhony Romilio
The geochemistry of the rocks, great for forming prints, was poor for fossilizing bones and teeth. We have no other records of the dinosaurs that made these prints, either at Walmadany or elsewhere in WA. Some of what has been found resembles tracks seen on other continents, but other prints appear to be from entirely unknown species. Salisbury told IFLScience: “I like to think the bones are out there somewhere,” but in the meantime, work continues on trying to match up those prints made on a single occasion to learn how the makers were moving and interacting with other members of their same, or different, species.
The company proposing the gas processing plant dropped the idea in 2013, but the Western Australian government continued trying to acquire the area in the hope of using it for industrial development in future. Salisbury's work, in combination with a recent change of government, could see the area protected forever, although rising sea levels may make some prints even harder to study.
The incoming tide makes it hard for scientists to study the footprints, like this one of Walmadanyichus hunteri, but certainly makes them look pretty. Damian Kelly