Ancient horses may have possessed a much greater variety of gaits than most modern horses, the findings of fresh research suggests.
Over time, the horse appears to have lost these abilities, with the exception of certain gaited breeds.
Alan Vincelette, writing in the journal Fossil Record, describes his work in determining the gait of Miocene, Pliocene, and Pleistocene horses from fossilized trackways.
Vinceletee is an associate professor of philosophy with the Pretheology Department at St John’s Seminary in Camarillo, California. He describes himself having come to philosophy by way of biology, having been a research assistant at the University of Illinois at Chicago in Molecular Biology and at the San Bernardino County Museum in Paleontology.
Vinceletee noted that much work has been done on vertebrate gaits over several decades, with the knowledge applied to fossil tracks to learn more about the gaits of ancient animals.
There has been particular interest in dinosaurs and mammals such as cats, dogs, camels, and horses.
Vinceletee described his own work in which he sought to expand upon such studies, and in particular to investigate footprints laid down in sand by modern horses and apply the findings to determine the gaits of fossil horses, based on the tracks they left.
In his research, the footprints left in the sand by 15 horses of various breeds with various gaits were videotaped, photographed, described, and measured in order to determine characteristics useful in distinguishing gaits.
These results were then applied to two new sets of fossil footprints — those of the middle Miocene merychippine horse Scaphohippus intermontanus that he personally examined and measured; and those from the late Pleistocene horse Equus conversidens, previously illustrated and described in a 2007 study.
Vinceletee reports that E. conversidens had a fast gallop of around 9.4 meters per second, but it was the earlier horse, S. intermontanus whose four intriguing footprints left about 14.5 million years ago that were revealed to be quite unique.
“The quantitative and visual features of these prints are suggestive of a medium-fast gait involving apparent ‘understepping’ of diagonal couplets and hind feet that overlap the centerline,” he reported.
“The gait that most closely matches the footprints of Scaphohippus is the ‘artificial’ gait of a slow rack or tölt, or pace, around 1.9 meters per second, though an atypical trot of a horse with major conformation issues or which is weaving (swaying) from side to side is a less likely possibility.”
The evidence, he said, clearly pointed to this kind of gait as opposed to a trot. “It is unfortunate that only four impressions were preserved as a few more impressions could have provided additional evidence as to which gait was occurring in Scaphohippus,” he wrote.
“If Scaphohippus was indeed engaging in the ‘artificial’ gait of a rack or tölt, or a pace, then it seems earlier horses were quite ‘gaited’ and had laterally coupled gaits naturally available to them.”
There could be several explanations for why this horse was engaging in a rack or slow pace, he said. “A pacing gait is sometimes seen in animals that are juveniles, weak, or fatigued. Hence some foals pace before learning how to trot. Still the horse tracks of Scaphohippus match the size of adult coffin bones, and so they do not seem to be that of an overly young horse.”
Vinceletee noted that his findings aligned with those of a 1984 study of Elise Renders, who found the artificial gait of the running walk displayed by Pliocene hipparionine horses, which is not a natural gait of horses.
It would seem, he said, that ancient horses possessed a much greater variety of gaits than modern horses and that over time they lost these abilities with the exception of certain gaited breeds.
“Such alternative gaits could have been useful to early horses as they allow horses to travel at a similar or faster speed than in the trot but with less expenditure of energy.
“Such gaits, though not as stable as the trot, may additionally have been useful in allowing fast speeds over varied or uneven terrain for they allow the horse to switch between a lateral and diagonal limb support structure and keep one foot on the ground at all times.”
This, he said, is one reason the tölt is useful in Iceland, with its varied volcanic and glacial outcroppings, and why the pace is beneficial in camels on the sand dunes.
“Another possibility is that Scaphohippus was an early grazing horse, and it may have quickly developed long legs but with a relatively short body and hence found the rack or slow pace more efficient or a way to avoid limb interference, as in camels or dogs.”
He continued: “The possibility that ancient horses could rack or tölt or pace (as well as display the running walk) is an interesting find in light of recent studies in horse genetics indicating that modern horses possess a so-called ‘gait-keeper gene’ (DMRT3) that limits the gaits and speeds of which they are capable.”
In gaited horses, the DMRT3 gene has a mutation that results in a shorter and less functional protein unit. The normal DMRT3 gene yields a protein that is active in the spines of mammals and helps to coordinate their limb movements between front and hind and between the opposite sides of the body.
The mutated form of the gene makes it harder for young animals to coordinate their hind limbs and transition to a gallop.
“Hence horse breeds with the mutation, such as Standardbred, Paso Fino, and Icelandic horses, can more easily learn to pace or engage in some other ‘artificial’ gait.”
The mutated DMRT3 gene has even been tracked back to a presumable first appearance in ninth-century England, based on 2016 research.
“As wild horses also possess the normal DMRT3 gene, the fact that earlier horses could rack or tölt suggests there may be more to the story genetically, and perhaps horses developed genes that limited their gait possibilities but allowed for the easier development of the three standard gaits of walk, trot, and gallop as this was beneficial to their survival.
“In any case, more recent studies have suggested a more complicated genetical picture for horse gaits as other genes than DMRT3 seem to be involved in such gaits as the fox trot and whether or not a horse has a tendency to trot or pace.”
Vinceletee said other fossil horse hoof prints that have been examined, diagrammed, or photographed are not fully gaitable, by his estimation. “They often occur as single impressions or couplets, in which case reconstructing the exact gait is not possible.”
He acknowledged that determining the gaits of fossil horses from their tracks can be difficult as trackways may be trampled upon by other animals. Thus,isolating individual sequences of prints can be challenging.
Typically, there are not enough footprints preserved to make gait determination possible. “Still, as has long been noted, gaits involve unique patterns of limb coordination and footfalls, and these are often reflected in observable patterns in footprints made.”
Quite extraordinarily, it appears that Miocene to Pliocene horses did not just walk and presumably trot and gallop, but could also engage in the so-called “artificial” gaits of the rack or tölt and running walk.
“All of this suggests that early horses were clearly ‘gaited’ and capable of a wide range of gaits, perhaps helping them outmaneuver prey on different terrains and also effectively migrate from place to place.
“This wide range of gaits available to earlier horses seems to have been reduced in modern breeds through selection and breeding, thus reducing the pool of available gaits to the four natural gaits (walk, trot, canter, gallop) found in most horse breeds.
“At any rate it is hoped that this study, in combination with those of others, will help resolve gaits exhibited by fossilized horse prints in the future.”
Vinceletee said further work would be beneficial on living horses in terms of measuring the exact speed of the gait via videos or speed guns and correlating this with gait variations.
He said much more work needs to be done on the kinematics and characteristics of the slow gait, rack, pace, and fox trot in the moving horse and associated footprints at slow and fast speeds.
In addition, studies of hoofprints made by unshod horses would be desirable as these would mimic the natural state of extinct horse species.
Determining the gait of Miocene, Pliocene, and Pleistocene horses from fossilized trackways, Alan Vincelette. Foss. Rec., 24, 151–169, 2021, https://doi.org/10.5194/fr-24-151-2021