A robotic version of a creature that lived about 290 million years ago may lead us to rethink an important evolutionary event in our past. It suggests animals with four legs could have gained advanced walking skills before they had fully turned their backs on life in water.
Some reptiles and amphibians look superficially similar when they walk, because their legs are sprawled out on either side of the body. In detail, though, amphibians tend to move inefficiently with their legs held mostly horizontal and their bellies very close to the ground. Many reptiles, in contrast, hold their legs a little more vertically and raise their bellies further off the ground for a more energy efficient walking style.
John Nyakatura at the Humboldt University of Berlin and his colleagues may have helped pin down when this change occurred. They have studied an ancient animal called Orobates that, in evolutionary terms, lies on a branch between the amphibians and the reptiles. It may even have had to return to water to lay its eggs as amphibians still do, meaning it may not have been completely adapted to life on land.
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But even though Orobates may not have lived on land for its entire life, Nyakatura鈥檚 team suspects it actually walked like an energy efficient reptile. They reached this conclusion by taking advantage of the fact that we have near-complete fossils of the Orobates skeleton, and also fossilised footprints left by the animal.
Using the shape of the skeleton and the pattern of the footprints as a guide, the researchers developed OroBOT. This is both a computer simulation and a physical robot modelled on the Orobates skeleton, and it is capable of generating a pattern of footprints identical to the fossilised trackways.
But it wasn鈥檛 enough that OroBOT reproduced the Orobates footprints. It was also necessary to make sure it did so in a biologically realistic way. To ensure that OroBOT walked like a real animal, Nyakatura鈥檚 team looked at the way living amphibians (salamanders) and reptiles (skinks, iguanas and caimans) walk, and used the information to put constraints on their robot鈥檚 walking style.
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Having done this, they found that OroBOT 鈥� andpossibly聽Orobates itself 鈥� walks in the ancient footprints most comfortably if its sprawling legs are relatively vertical and its belly is high off the ground, making its walking style look a bit like that of a caiman.
A few researchers have previously suggested Orobates might have had the 鈥榓dvanced鈥� walking style of a reptile, but they hadn鈥檛 backed the idea up with hard data, says Nyakatura. 鈥淎nd others assumed that advanced locomotion only appeared after the origin of [completely terrestrial four-legged animals],鈥� he says.
OroBOT strongly suggests it was the other way around: animals with four legs evolved efficient walking before they severed their ancestral link with watery environments.
The approach the researchers used could throw light on other important evolutionary changes in the way animals move, including the origin of bird flight and the origin of upright walking in hominins 鈥� which means we might see robotic versions of other extinct animals soon.
Nature
