Cretaceous footprint debate

Now an Australian team, from the Australian Age of Dinosaurs Museum of Natural History in Winton, Queensland and the University of Newcastle in NSW, has attempted approach the problem from a completely different angle.

They have use the nearly complete fossilised foot bones of Australovenator – Australia’s most well-understood carnivorous dinosaur, and a species that lived 95 million years ago – to recreate a lifelike model of the entire foot including the muscles, ligaments, skin and other soft tissues.

They then used this reconstruction to create footprints in muddy sediments thought to be similar to those that record thousands of dinosaur footprints at a trackway site called Lark Quarry in Queensland. This site is 110km south-west of Winton, where the bones of Australovenator were first discovered more than a decade ago.

Nobody has created such a detailed reconstruction of a carnivorous dinosaur foot before, says Dr Matt White – lead author of a new paper describing the work in the journal PeerJ – nor used it to establish the range of motion of a foot including soft tissues in addition to the bones.

“I always wanted to work out the biomechanics of this animal, and since we had a fossil foot it was a great place to start. We used a dissection of an emu foot to work out the proportions of the muscles and tendons of the Australovenator foot,” White says, adding that his work has shown it’s possible to accurately reconstruct dinosaur feet using knowledge from modern, fast-running birds and “work out how muscles and tendons effected the range of motion of the skeletal elements”.

The foot was reconstructed using 3D software on a computer and then the computer model was used to create a synthetic replica, with a skin texture based on impressions known from other carnivorous dinosaurs. “Now we had a complete theropod foot so we could create its corresponding foot prints and compare them to an actual trackway,” White says.

The thousands of dinosaur prints found at Lark Quarry were the inspiration for the stampede scene in the 1993 movie Jurassic Park. The original interpretation of the tracks was that they represented a stampede that had occurred when a large carnivorous dinosaur chanced upon a mixed herd of so-called ornithopod herbivores around a waterway.

But a study published by researchers from the University of Queensland in 2013 challenged that hypothesis, arguing that tracks might merely have been left by animals migrating across the waterway, and that the largest tracks were not left by a carnivore but a large herbivore similar to the species Muttaburrasaurus.

Using a sediment mix that they deemed to be similar to the original mud the Lark Quarry tracks were pressed into, White and his co-workers created tracks with their reconstructed Australovenator foot including full foot impressions as well as heel slides, scale imprints and claw drag marks.

“The footprints we created with the foot were a close match to those of the 11-print trackway [left by a larger dinosaur] at Lark Quarry,” White argues. “Therefore, those tracks were most likely made by a theropod carnivore as originally stated, rather than the more recent interpretation of being created by an ornithopod.”

Other dinosaur scientists contacted by Cosmos were not yet convinced the work proved the prints were left by Australovenator.

Dr Steve Salisbury, one of the co-authors of the 2013 revised interpretation of Lark Quarry, says: “Using a model of a dinosaur foot to test how different types of tracks might be made seems like an interesting idea. But whether the results of this study solve the identity of the large Lark Quarry trackmaker is still debatable. We know that the large tracks at Lark Quarry most closely resemble tracks from elsewhere that are typically assigned to ornithopod dinosaurs.”

Salisbury says it would have made sense to also attempt to reconstruct a Muttaburrasaurus foot to compare the tracks left by it alongside those made by the model of Australovenator.

He adds that care should be taken in studying the fine detail of the of the Lark Quarry tracks, as “many of the large tracks have been damaged over the years, and the surface has been repaired with concrete. For this reason, archival photos and casts are much more reliable.”

White agrees that reconstructing a Muttaburrasaurus foot would be an interesting next step in this research, but says that this is not yet possible, as no complete fossil foot for the species exists. A final answer to the mystery of who left the Lark Quarry footprints may have to wait for future fossil discoveries.