Reconstructing locomotion with fossils, footprints, and... robots?
November, 2019, by guest author Armita Manafzadeh, PhD Candidate in Ecology and Evolutionary Biology at Brown University
The skeleton of Orobates pabsti. Source: THOMAS MARTENS/MUSEUM DER NATUR GOTHA
Right around 350 million years ago, long before the evolution of dinosaurs or mammals, animals that looked a lot like oversized amphibians started colonizing dry land. Over the past few decades, scientists have discovered many more fossils of these critters and learned about their anatomy and diversity. But we're still not quite sure how our earliest four-legged cousins walked — did they slink around on their bellies, like salamanders, or did they hold their legs underneath their bodies, more like crocodiles? And what does this mean for the evolution of terrestrial locomotion? A recent study brings us a big step closer to the answer.
Where's the evolution?
Paleontologists typically use either an extinct animal's bony anatomy or its footprint trackways to piece together how it moved. This is where most existing hypotheses about the locomotion of early terrestrial vertebrates come from. But if paleontologists are really lucky, they might find both the skeleton and the footprints of the same animal — and this is the case for a four-legged herbivore called Orobates, which lived almost 300 million years ago in what's now central Germany. In early 2019, a team of researchers from Germany, Switzerland, and the UK took advantage of this unique opportunity to create a new approach for reconstructing locomotion.
A fossil trackway created by Orobates pabsti Source: Credit: SEBASTIAN VOIGT/URWELTMUSEUM GEOSKOP THALLICHTENBERG
The researchers first used information from the shapes of Orobates' bones and the positioning of its footprints to create 3-D computer simulations of many potential gaits, or ways of walking. By preventing Orobates' bones from bumping into each other and controlling parameters like how much its spine could bend and how much power it used to walk, the team was able to rule out many gaits that were impossible or unlikely based on studies of extant animals. Then, they tested gaits that still seemed possible by building a robot (affectionately named OroBOT) to check if they could truly create trackways like those in the fossil.
The team's combination of computational and robotic analyses led them to conclude that Orobates walked fairly upright, more like a crocodile than a salamander. This outcome was surprising because most scientists have assumed that early vertebrates had to drag themselves along the ground, and that more "advanced" modes of locomotion didn't evolve until millions of years later. But in the light of these results, we now understand that animals didn't steadily progress towards upright locomotion — rather, many locomotor styles evolved early on in vertebrate history.
Nyakatura and colleagues' computer simulation and robot. Source: Wired Magazine
Discussion and extension questions
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