Paleontology innovation reveals strange truth about how dinosaurs walked

Though a certain species of mammal clad in suits and ties are all the rage now, for much of Earth's history the planet was dominated by towering, scaled (or feathered) creatures. Yet for all our movies, figurines, and general obsession over dinosaurs, paleontologists know so little about these creatures' lives.

A new 3D imaging technology called XROMM — X-ray Reconstruction of Moving Morphology — could help bring the lizards back to life. In a paper published Monday in the journal Proceedings of the National Academy of Sciences, a team of scientists from Brown University describe a new way to use this tech to recreate the locomotion of ground-treading archosaurs, a group that once included sauropods like Diplodocus and Brontosaurus. What they found reveals an unexpected connection between these massive lizards and a more pedestrian creature: ducks.

After analyzing 600,000 joint poses two extant dinosaur relatives — the Helmeted Guineafowl and American alligator — the researchers identified a specific set of joint movements their ancient dino ancestors would have likely used to get around.

Why it matters — Movie dinosaurs have a lot to answer for when it comes to perpetuating myths about these creatures, and this study goes some way to help clear up the misconceptions about locomotion. But it also provides a better understanding of how these ancient reptiles moved. That helps paleontologists paint a clearer picture of their evolution, and how these "ruling dinosaurs" ultimately ended up as swamp critters and farmyard fowls.

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Here's the background — To reverse-engineer the lives of ancient dinosaurs, paleontologists can try to reimagine how static, fossilized joint bones may have moved hundreds of thousands of years ago. But by their very nature, these old bones only tell scientists so much — in fact, they are often better at describing what these dinosaurs couldn't do, instead of what they could.

Musculoskeletal models or robotic simulations can help, but these, too, only take scientists so far. To get around these problems, in 2015 a team of Chilean researchers famously strapped a popsicle stick to a chicken's butt to see if it walked like a dinosaur — it did. But again, there is some serious inferring from results happening here.

So the researchers behind this paper take yet another, more high-tech approach. Armita Manafzadeh, a Ph.D. candidate in ecology and evolutionary biology at Brown University and lead author of the research, explains in a statement this new X-Ray technology could finally bridge these gaps.

"By combining the latest technology for studying joint motion with unprecedented amounts of joint pose data, we've uncovered surprising new information that will improve reconstructions of locomotion in extinct animals," Manafzadeh says.

This data driven approach can help scientists answer fundamental questions of evolution "like how animals with backbones came out of the water and started walking on land, how they went from walking on four legs to two, and how flight evolved," Manafzadeh says.

What they did — The researchers took X-ray videos of both alligators and Guineafowl walking, and having their limbs manipulated. They also took CT scans of the animals' skeletons and transferred both datasets to XROMM for 3D reconstruction.

XROMM analyzed close to 600,000 joint poses for the two animals. The researchers then used these data to create joint mobility maps, enabling them to look for patterns of hindlimb movement shared by these many-times-removed dinosaur relatives.

What they discovered — With this new mobility data, the researchers uncovered two important similarities in both the gait of Guineafowl and alligators.

1. Both animals appeared to favor a narrow center of mobility.
2. Both show patterns of abduction — movement away from the body's midline — during movement and weight-bearing stances.

A narrow center of mobility may mean dinosaurs also have little to no potential for locomotion outside of these ranges.

From the abduction data, the researchers theorize that, if dinosaurs had similar movement, then it's likely that they would've run a little duck-footed.

What's next — Now that they've tested XROMM out on the animals' hindlimbs, the researchers plan future experiments to test their new technology on other outstanding questions in paleontology, like how dinosaurs' forelimbs would've moved, or how pterosaurs might have used their joints to fly.

"We've given our colleagues the tools to improve their reconstructions of extinct animals, and to test whether their existing hypotheses about locomotion fall into the patterns we find," Manafzadeh said. "But our next big goal is to figure out why these patterns exist."

Abstract: Reconstructions of movement in extinct animals are critical to our understanding of major transformations in vertebrate locomotor evolution. Estimates of joint range of motion (ROM) have long been used to exclude anatomically impossible joint poses from hypothesized gait cycles. Here we demonstrate how comparative ROM data can be harnessed in a different way to better constrain locomotor reconstructions. As a case study, we measured nearly 600,000 poses from the hindlimb joints of the Helmeted Guineafowl and American alligator, which represent an extant phylogenetic bracket for the archosaurian ancestor and its pseudosuchian (crocodilian line) and ornithodiran (bird line) descendants. We then used joint mobility mapping to search for a consistent relationship between full potential joint mobility and the subset of joint poses used during locomotion. We found that walking and running poses are predictably located within full mobility, revealing additional constraints for reconstructions of extinct archosaurs. The inferential framework that we develop here can be expanded to identify ROM-based constraints for other animals and, in turn, will help to unravel the history of vertebrate locomotor evolution.