The motor abilities of four-legged animals largely depend on the ability of their nervous system to precisely coordinate the motor skills of the skeleton and muscles. This can be seen from the outside: if you look closely at the movements of the limbs of the crocodile, you can see that they are far from being as smooth, accurate and economical as the movements of a cat.
Professor of New York University of Technology Michael Granatosky was the first to connect this difference in the differences in the structure of the peripheral nervous system of mammals, on the one hand, and more "primitive" reptiles and amphibians, on the other. An article prepared by him and his colleagues was published in the Journal of Experimental Biology.
The fact is that at the junction of muscle fibers and tendons, tetrapods have special receptors - Golgi organs. They monitor muscle tension, signaling dangerous stress that could damage it. In amphibians and reptiles, the Golgi tendon organs are distributed throughout this area. However, in birds and mammals, they are found directly in the muscle-tendon junction.
Scientists have suggested that this allows more "complex" tetrapods to more accurately register stretching and provide increased control over movement. “These structural differences have long been known, but so far no one has thought about the implications they have for animals,” says Professor Granatocki.
To find out, biologists collected and analyzed data on the motor activity of representatives of 55 species. In particular, they looked at the statistics of stride length, finding that in a reptile or amphibian, it can vary quite noticeably. But mammals move on a flat surface with almost equal, precise movements.
Such accuracy, apparently, not only increases the dexterity of the animal, but also saves energy, increases the controllability of falls, and reduces trauma. Scientists even suggest that it was precisely the features of the anatomy of the peripheral nervous system that allowed birds and mammals to significantly reduce the mass of their skeleton, which has become many times lighter than that of reptiles of comparable size.
“The bones of reptiles and amphibians are capable of withstanding loads that are ten times their own weight, while in birds and mammals only 2.5 times,” notes Michael Granatocki. “Perhaps they got a lighter and less energy-intensive bone structure precisely because they no longer needed a heavy protective frame.”