One study reveals that one species of ray uses the same neurons to walk as terrestrial animals. This is a new clue to the passage from the sea to the land of the oldest vertebrate ancestors.
Since marine environments are highly believed to be the cradle of life, how do you explain the passage from the sea to the land of our oldest biological ancestors? Even if this mystery remains far from being solved, a recent study published on Cell suggests that the first marine species already knew how to walk before adapting to terrestrial environments.
Jeremy Dasen’s team, a neuroscientist at the University of Medicine in New York, has studied Leucoraja erinacea, a species of ray that can walk in the seabed to find food. While the majority of fish use the muscles of their bodies to move through the water by waving their spine, the fish uses its anterior fins which it uses as “paws” to advance on the sea floor.
The scientists then had the idea to study the brain of the animal. Surprise: rays use exactly the same neurons to walk as terrestrial vertebrates. In addition, they noted that the common ancestor of this species has separated from the four-legged tetrapods, which are mammals, birds, amphibians and other reptiles, 420 million years ago. In other words, the neural circuit essential to provide walking ability in current land animals already existed in fish before they were adapted to terrestrial environments.
In addition to the neurons, Leucoraja shows other anatomical similarities with the tetrapods in its way of walking, namely a left-right alternation and a reciprocal extension-flexion of its fins. For the moment, it is difficult to establish a definitive scenario on the passage sea / land of our ancestors. Nevertheless Dasen, interviewed by Science, is astonished: “This discovery is rather remarkable (…) it is not as if the tetrapods needed to invent a totally new system to walk. They already had several main elements in place ( …). ” In short, the best way to walk is not new.