Few people gallop; the equine pace is usually reserved for small children imitating horses or fitness courses. Galloping, on the other hand, is an important part of the repertoire for camels, lions, and giraffes as they progress through the gears.

While galloping is one example of an “asymmetric gait,” Eric McElroy from the College of Charleston, USA, explains that the timing of footfalls is unevenly spread, including bounds performed by rabbits, crutching by amphibious fish, and punting, where fish press themselves along the sea- or riverbed with their pelvic fins.

Scientists previously thought that mammals only developed the capacity to bound and gallop after they initially existed on the planet 210 million years ago.

When McElroy and Michael Granatosky of the New York Institute of Technology in the United States discovered that crocodiles and turtles can gallop and bound at their fastest speeds, they wondered whether animal coordination may have evolved earlier than previously assumed.

They report their findings in the Journal of Experimental Biolog, claiming that animals presumably gained the capacity to crutch, bound, and potentially even gallop 472 million years ago, long before life appeared on land.

To find out, the researchers combed through the scientific literature and created a custom family tree, which includes mammals, marsupials, monotremes, reptiles, frogs, toads, and fish that are currently known to propel themselves along surfaces with their feet and fins using asymmetric ‘foot falls.’

“In total we compiled data from 308 species,” McElroy adds, assigning a score of 0 to species that only employed evenly timed walks, trots, and runs, and a score of 1 to species that bound, crutched, punted, or galloped asymmetrically. After that, the researchers ran a series of simulations to see if asymmetric gaits appeared earlier or later in the evolutionary tree.

“It took months to work out all the kinks in the analysis,” says McElroy, who discovered that the oldest ancestors of almost all extant creatures, including fish, were most likely capable of moving with a proto-asymmetric gait 472 million years ago.

It’s unclear if the animals were punting, crutching, or bounding along the seafloor, but they were able to propel themselves by asymmetrically coordinating their limbs.

Even though our earliest ancestor may have been capable of this alternate form of propulsion, some animals, including lizards, salamanders, frogs, and even elephants, have lost the ability to bound and gallop, despite having ancestors who were capable of coordinating asymmetric movements in their family tree.

As a result, the capacity to bound and gallop isn’t limited to animal species. Almost all creatures alive today have asymmetrical ancestors, however, some lost this capacity somewhere along the way, either because they lost the nerves necessary for coordinating these moves or because they grew too huge or too slow to fly.

In any case, mammals are not the only creatures capable of coordinating asymmetric movements, and it’s plausible that we got it from an early fishy ancestor who drove itself down the seabed on its fins long before any other species set foot or fin on dry land.

Source: 10.1242/jeb.243235

Image Credit: Getty

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