New research offers insight into why horses evolved from having four and three toes per foot to only one hoof.
According to the study, as horses evolved from dog-sized to weighing more than 1,000 pounds, it became efficient to have one strong toe to support their weight rather than multiple small ones. Additionally, hooves force horses to carry weight at the ends of their legs, making it easier for them to maneuver.
In order to test these ideas, researchers at Harvard University scanned leg fossils from 12 different varieties of horse, including modern horses and their 55-million-year-old ancestors.
The researchers previously studied how horses stress different limbs throughout movement. Then, they created models to visualize forces acting on lower legs and toes throughout horses’ evolutionary history.
Early horses had more even toes and they helped carry weight. As they became larger over time, the toes on the sides of each foot began to shrink while the center became stronger to support extra weight.
Researcher Brianna McHorse, a PhD candidate at Harvard, told The New York Times that the study does not answer why the side toes vanished, but says that it would have made it easier for horses to maneuver their legs faster.
Regardless of the number of toes, horses are an anomaly for their size and agility.
“If I had no knowledge of horses and you said, ‘Hey there’s this animal that’s a big grazer and only has one toe,’ I would probably not expect it to be capable of the kind of speed and jumping and other athletic feats that horses are capable of,” McHorse says.