The vanishing toes: modern horses bid farewell to extra digits

Scientists share the fascinating journey that transformed horses from multi-toed ancestors to the sleek, single-toed creatures we admire today.
Abdul-Rahman Oladimeji Bello

Scientists from the UK, the US, and the Netherlands have confirmed that modern horses have indeed lost their additional toes, settling a long-standing debate in evolutionary biology.

The study, published in the prestigious journal Royal Society Open Science, sheds light on the intriguing transformation horses underwent over millions of years.

The story begins with the ancient ancestors of horses, creatures like the Eocene Hyracotherium, which boasted feet resembling those of modern tapirs—four toes in front and three behind, each with an individual hoof and an underlying foot pad.

However, as time passed, these extra digits gradually disappeared, leaving modern equids, such as horses, asses, and zebras, with only a single toe on each foot.

To unravel this evolutionary mystery, the international researchers carefully examined hoof prints and foot bones from living horses and fossil records. Their findings strongly support the notion that the lost toes have vanished completely rather than being somehow retained within the hooves, as proposed by a recent paper.

Professor Christine Janis from the University of Bristol’s School of Earth Sciences explains, “In later fossil horses, there were only three toes at the front and back. These extra toes, known as side toes, were smaller than those of a tapir and likely did not touch the ground under normal circumstances. However, they might have provided support during exceptional situations, such as sliding or forceful impact.”

Lead author Professor Alan Vincelette of St. John’s Seminary in Camarillo, California, further clarifies, “Although the previous 2018 paper suggested that remnants of the side digits were retained within the hoof, our research demonstrates that the lower portions, or toes, have been lost over time.”

The vanishing toes: modern horses bid farewell to extra digits
Modern horses with one toe

The study also discredits the idea that the side toes contribute to the frog, a triangular structure on the sole of the hoof that acts as a shock absorber. While earlier research proposed this hypothesis based on the analysis of hoof prints from an extinct three-toed horse named Hipparion, the new findings challenge this interpretation. Contrary to the earlier claims, many hoof prints made by three-toed horses exhibit a distinct frog.

Professor Christine Janis comments, “While the notion that modern horses have retained all of their original toes as within-hoof remnants are appealing, it can be shown to be incorrect.”

Professor Vincelette adds, “The frog of the horse's hoof evolved independently of the side toes as a unique structure providing shock absorption and traction during locomotion.”

Intriguing difference between one-toed and three-toed horses.

In addition to settling the toe debate, the researchers discovered another intriguing difference between one-toed and three-toed horses. The feet of modern one-toed horses have a rounder shape compared to the oval shape of the main toe in their three-toed ancestors. This divergence in shape may be related to differences in weight distribution and ecological habitat.

This brings us one step closer to understanding the remarkable journey of horse evolution. The disappearance of their additional toes has transformed these majestic creatures into the graceful, powerful beings we know today. As we delve deeper into the mysteries of the natural world, we uncover the captivating stories hidden within the traces left by our ancient ancestors.

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