让化石“迈开腿” |Nature Podcast 学术资讯

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Host: Benjamin Thompson

Somewhere around the late Devonian era, perhaps 360 million years ago, vertebrates started to invade the land, dragging themselves out of the water and expanding into pastures new. The first land invaders were likely to be pretty hopeless at moving about on land but as time went on, terrestrial creatures would evolve, developing ever more sophisticated mechanisms for getting about. But what did that evolutionary journey look like, and how can we know? We may be able to see fossils of creatures which were present at the time, but there is a big difference between a pile of bones and a moving animal. Now, a team lead by John Nyakatura from Humboldt University in Berlin has used a host of techniques to try and work out how a crocodile-like creature from about 280 million years ago might have moved, in the hopes of better understanding the great transition to land. Noah Baker called him up to find out more.

Interviewer: Noah Baker

Tell me about the animal that you’ve been studying in this particular paper?

Interviewee: John Nyakatura

We have been studying Orobates pabsti from the Lower Permian, about 300 million years old, and it’s a beautifully preserved fossil, complete and articulated. And moreover, there’s fossil trackways which have been assigned to Orobatesfrom the same fossil locality which is very rare.

Interviewer: Noah Baker

What was your approach to work out how this creature might have moved? What was the first step I suppose?

Interviewee: John Nyakatura

We used a highly multidisciplinary approach. First, we were interested in how modern animals use sprawling tetrapod locomotion, so we studied four modern species, extant species, which were quite different in terms of their morphology, or anatomy and also in terms of their ecology and in terms of their position within the tree of life. So, we studied salamanders, the blue-tongued skink, green iguanas, which live in trees actually, and then we studied spectacled caimans, which are much closer to the water. By studying these very different modern animals, we were able to identify general principles of their biomechanics of locomotion, and we assume that if animals today, which are so diverse, have these general principles, that these general principles also applied to the fossil. So, we used this information as a guideline for our simulation study.

Interviewer: Noah Baker

So, you started off by looking at these extant animals and you developed these sort of four key parameters, and then you wanted to look at how the Orobates itself would fit in and to do that you needed to get an understanding of what that skeleton looked like digitally. Tell me what you did there.

Interviewee: John Nyakatura

Yeah, so we used highly precise computer tomography scans to first scan the original fossil, and then derive a digital, three-dimensional skeleton from it.

Interviewer: Noah Baker

And then from that digital skeleton, you can start looking at the way that the bones might have moved, the sort of range of motion of the joints.

Interviewee: John Nyakatura

Right. The range of motion of joints is one thing, but it does not restrict the movements very much. If you just think about, so some people are able to do the splits, right, with their legs, but during normal locomotion they don’t do the splits. So, usually the range of motion in the joints does not constrain the actual locomotion very much, so the trackways are much more helpful in this regard. Therefore, we forced our animated skeleton to move within these trackways, and according to the general principles of sprawling tetrapod locomotion that we observed in the modern animals.

Interviewer: Noah Baker

Okay, so you can animate your digital skeleton to walk inside the trackways – these sort of fossilised footprints – and then you can use the information you’ve learn from extant species to further narrow down various parameters of the walking, like precision or power or balance. But then you still wanted to go one step further, and that’s to prove the kind of theories you’ve come up with from your simulation in the real world. Tell me, what did you do there?

Interviewee: John Nyakatura

Yeah, so simulation is one thing, but to actually prove it in the real world is a different thing. So, the first thing we did is build a robot that actually is able to do all the movements that we also simulated. And of course, there’s friction, there’s gravity, there’s lots of things that act on the locomotion of a physical robot and we wanted to show that the reconstructed gaits that we find likely can be produced by the robot and then we check whether the robot has produced the trackways that we can also find in the fossil record. And by this, we tested our hypothesis a bit about these fossil trackways and the trackmaker.

Interviewer: Noah Baker

Okay, so bringing all of those many different methods together, tell me, did you come up with an answer? How do you think Orobates might have walked?

Interviewee: John Nyakatura

It’s very likely that Orobates already had what we termed ‘advanced locomotion’. So, it was probably lifting its body off the ground quite a bit. It was fairly energy conservative in terms of its locomotion, and in many ways what we found for Orobates resembles what we also found in doing the locomotion of the spectacled caiman.

Interviewer: Noah Baker

And do you know what this sort of more upright gait might mean for Orobates in terms of how it lived?

Interviewee: John Nyakatura

The way to interpret it is not that easy, but it suggests that Orobates probably was quite independent from water. It had a quite effective locomotion on land, and this is something that modern species, we usually don’t see in amphibians.

Host: Benjamin Thompson

That was John Nyakatura speaking with Noah Baker. You can see the Orobatessimulation and its robotic counterpart in action in a video on our YouTube channel. Check it out at youtube.com/NatureVideoChannel.ⓝ

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