Like cheetahs, ancient ocean creatures may have moved at a gallop

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Cheetahs are the fastest animals on earthpointing at speeds over 60 miles per hour. Salamanders, by comparison, run at a much more measured pace. While cheetahs are exponentially bigger and stronger than salamanders, another big difference between the two is the way they move – their gait.

When cheetahs hunt prey, they move with an asymmetrical gait – specifically, they gallop, much like horses – with their forelimbs and hindlimbs moving in pairs. Salamanders, on the other hand, run with a symmetrical gait, their left and right limbs moving opposite each other.

Historically, scientists believed that symmetrical gaits were evolutionarily older – the salamanders being the model for how early land animals moved. Conversely, asymmetrical gaits such as galloping and jumping would have evolved independently in different species over time.

But new research points to a different story, one in which asymmetrical gaits existed in our jawbones. ancestors living more than 400 million years ago in the ancient oceans, long before vertebrates moved on land. the to work was published Tuesday in The Journal of Experimental Biology.

Asymmetrical gaits underlie the speeds reached by cheetahs, greyhounds and kangaroos. “That’s why so many people thought these were purely mammalian innovations,” said Michel Granatoskyevolutionary biologist at the New York Institute of Technology and one of the study’s authors.

Evidence, however, is mounting to suggest that asymmetrical gaits may not have arisen as recently as once thought, and were certainly not uniquely mammalian. Some species of crocodiles gallop, at least one species of sea turtle leaps underwater, and there are fish that walk along the ocean floor.

The African lungfish basically has little spaghetti noodles for the legs, but they walk on the bottom of the substrate,” Dr. Granatosky said. “And in about 10 steps, half of them will be symmetrical and the other half will be asymmetrical.”

This has motivated researchers to re-examine the evolution of asymmetric movement. From a sample of 308 living species of jawed vertebrates, including mammals, reptiles and others, the team constructed a tree of the evolutionary relationships between species. From there, they gave each species a score of 0 if it couldn’t move asymmetrically or a score of 1 if it could. They then tested a series of potential models for the evolution of asymmetric gait to see which best fit the data.

The model found to be the most likely placed no restrictions on the evolution of asymmetric gaits, with gains and losses from asymmetric gaits being able to occur freely over time.

“It’s a much looser model,” said Eric McElroybiologist at the College of Charleston and co-author of the study, and he showed about a 75% probability that the ancestor of jawed vertebrates over 400 million years ago had an asymmetrical gait, and that asymmetrical gaits could be both lost and acquired as jawed species evolved.

This finding is quite logical for Sudhir Kumar, a Temple University biologist who was not involved in the study. “In evolution, nothing is sacred,” he said. “We gain and lose characteristics based on our environment, based on our behaviors, based on our needs, and that’s what you see here – the way animals walk isn’t fixed. It evolves.

The researchers are open about the holes in their analysis.

“When you’re trying to estimate how something that’s been dead for 400 million years has moved around, there’s a bit of guesswork involved,” Dr McElroy said. Referring to the field of research, Dr Granatosky added: “We have an extreme mammalian bias in the way we sample biomechanical data.” Incorporating more data from non-mammalian species like fish could dramatically change their results, he said.

Although he acknowledges the study’s potential blind spots, Pedro Godoy, an evolutionary biologist at Stony Brook University who was not involved in the study, sees the work as an important contribution to understanding locomotion between species. “We can only fully understand the drivers of different gait types if we do so in the light of evolution,” he said.

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