Yes, it is common to think that the gallop is a typical movement of quadrupedal mammalian animals that began to inhabit the terrestrial environment 210 million years ago. Of course, nobody imagines a galloping fish . But a study proposes delaying the appearance of the gallop by more than 250 million years , ceasing to be considered an exclusively mammalian movement.
Horses, antelopes, camels, lions, giraffes… galloping is key for all of them. It allows you to travel great distances efficiently in relation to energy expenditure , quickly attack a prey, or flee when it touches a predator. We are used to seeing this graceful movement in documentaries about mammals. But have you ever wondered when mammals learned to run this way?
Galloping crocodiles. jumping turtles
In the history of the evolution of the species, the gallop is nothing more than a movement within the maneuvers called “asymmetrical marches” . This requires coordinating the limbs independently, since the moment the legs hit the ground is unequal for each limb. Until now it was believed that many of the quadrupedal mammals were the only ones capable of carrying out this form of displacement, but Eric McElroy (College of Charleston in South Carolina) and Michael Granatosky (New York Institute of Technology) have published a study in Journal of Experimental Biology in which they change our conception. They defend that many other animals, such as crocodiles, can gallop , just as there are turtles capable of jumping . It was this observation that led them to ask the question of when animals developed this ability.
The complexity of the matter
The difficulty in counting the asymmetrical movements of the limbs of animals, compared to symmetrical gaits, is one of the problems for which research on these movement mechanics has received little scientific attention.
The way in which the researchers approached their study was through a comparison between 308 species . They reviewed the scientific literature on the subject and found that until now no one had explored the evolutionary history of movements through comparative phylogenetics . So they collected data on mammals, marsupials, reptiles, toads, frogs and fish to create a family tree with current species capable of some kind of asymmetrical gait. The task was not easy, and they had to use simulations to try to detect and order the asymmetric movement modes that could appear in the evolutionary tree.
“ It took us months to solve all the problems in the analysis , but we found that it was most likely that around 472 million years ago , the first ancestors of almost all modern animals, including fish, were already able to move with some kind of gait. asymmetric ”, comment the researchers. “It is not known if they moved across the seabed by pedaling, with crutches or by jumping, but the animals were able to asymmetrically coordinate their limbs to propel themselves.”
unlearning skills
Among the surprises shown by this study is that of recognizing asymmetric coordination in species that had not yet left the seabed. As well as discovering that current species such as salamanders, toads, lizards or elephants have lost the ability to gallop despite coming from other species that did enjoy this ability. This phenomenon could be attributed to the loss of anatomical and muscular characteristics necessary to carry out such a movement or, in the case of elephants, that due to their enormous size and slowness in moving, it is impossible for them to undertake this rhythm.
The analysis is based on an evolutionary model whereby asymmetrical gaits would be ancestral to gnathostomes (that is, vertebrates with jaws) and these gaits would be gained and lost by the different species that would evolve from gnathostomes. This is one more piece of research whose results add to the growing body of work showing that early gnathostomes and tetrapods could have used a variety of gaits , including asymmetric limb cycling patterns.
References:
McElroy, EJ et al. 2022. The evolution of asymmetrical gaits in gnathostome vertebrates. Journal of Experimental Biology 225(1): jeb243235 . DOI: 10.1242/jeb.243235.
