Dinosaurs left behind many clues to their prehistoric lifestyles. But while their bones may provide stick-figure frameworks by which we understand their bodies, it's their footprints that record their movement in the places where they literally walked the earth. To understand exactly how dinosaur feet made dinosaur footprints, palaeontologists are looking to their living representatives: birds.

In this case, the birds are helmeted guineafowl, native to southern Africa, and their three-toed footprints closely resemble those of their extinct bipedal cousins, like T. rex. Simply by walking across a squishy pathway, these feathered lab assistants are providing Brown University researchers Stephen Gatesy and Morgan Turner with insights into how dinosaur tracks were formed.

Footprints are more than just a simple impression of a foot pushed into sediment: they're formed through a complex interaction of a moving foot and the yielding earth. Each print might be different depending on what animal left it, what they were stepping in and exactly how they moved their foot as they walked. This means scientists can learn a lot about dinosaur foot movement by examining the smushed sediments left behind – but they need to know what to look for.

"We'd like to be able to look at footprints in a smarter way than just: How long were their steps? How big are their feet?” said Gatesy during the Triassic-Jurassic Research Symposium last month at the Bruce Museum in Connecticut.

Gatesy has been studying bird locomotion for decades, and at first, he had a different bird in mind. "I was considering using chickens and my advisor, who was South African, said 'How about guineafowl? They love to run!'"

At Brown University, the guineafowl are presented with a four-metre (13ft) walkway which might be muddy or grainy, soft or firm. At one end is a person annoyingly dangling a glove on a stick, and at the other end is a dark, comfortable-looking enclosure. As the birds strut their way from one end to the other, they leave real-life dinosaur footprints behind them, and their movements are captured by a combination of regular-light cameras and X-ray ones.

For a track to form, the foot typically needs to sink, sometimes quite deeply, into the ground. This means a lot of the foot movement is happening under the surface, and the X-ray cameras allow the scientists to peek at this hidden motion. "By using X-ray reconstruction of moving morphology (XROMM)," Turner explained, "we are actually able to look below the ground."

After scanning lots (and lots) of bird steps, the researchers are starting to get an idea of how the foot moves through the ground, and what features are left behind in the layers of the final print.

One bird can leave a variety of footprints depending on how it's moving and what it's stepping in. All of these varied prints hold clues to the motion of the dinosaur that left them. Image: Stephen Gatesy

Armed with this sort of information, they can start comparing bird tracks to dino tracks. Gatesy, for example, has been examining the famous "Primeval Bird" tracks of Connecticut Valley, and has been able to identify features such as where the foot entered and exited the sediment, and which parts of the footprint have been lost to time and erosion.

"I think that work is incredibly important," said Paul Olsen of Columbia University, who has been collecting dinosaur footprints from the Northeast United States for many years. "[This is] because when it comes down to it, the footprints are the only record we have of the living, moving non-avian dinosaurs." 

A lot of messy-looking tracks have so far been ignored by palaeontologists for being "imperfect" and not suitable for identifying the dinosaurs that left them, Olsen explained. "What I learned from these guys is that you can get the motion of the living animal from those same footprints that I used to think were useless," he said.

As for the team's decision to work with guineafowl, Olsen approves: he's performed similar research with chickens ... and found them somewhat less cooperative. "The most common behaviours were just standing there on the clay, and then you'd try to get them to move, and they'd move vertically!"

This research is still in the early stages, and the team has a lot more to learn from their birds. Turner also anticipates getting other animals involved – after all, not all dinosaurs had bird-like feet. "I'm interested in pushing further into working with alligators," she said.



Top header image: Amelia/Flickr