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Scientists determine how animals are related by comparing the characteristics they share or don’t share. It behooves you to know that horses belong to a group of mammals called ungulates, which are animals with hooves, or hard coverings that protect their toes and are an amazing feature for running.

Ungulata is a clade, meaning all of its members share a common ancestor. This clade is split into two major groups: Those with an even number of toes and those with an odd number of toes. When talking about ungulates, it’s important to…

Know your toes!

These are both hooves, but not all hooves are alike. Some hooves protect an even number of toes. Some hooves protect an odd number of toes.

Hoofed animals with an even number of toes are called artiodactyls. Artio means “even numbered” in Greek, while daktylos means “toes,” hence the name. Other members include goats, pigs, hippos, deer, camels, llamas, giraffes and many other species. Cetaceans, the order that includes dolphins and the killer whale, are also artiodactyls!

Hoofed animals with an odd number of toes are called perissodactylsPerissos means “odd numbered” in Greek. That means that the closest living relatives of the modern horse are its fellow perissodactyls, the rhinoceroses and tapirs.

Let’s take a look at their closest living relatives:

Horse hooves over time

Now that we know about other perissodactyls, let’s take a deeper dive into horses.

Although all horses are perissodactyls, they have differed through time as to the actual number of toes each genus had. Most early horses had 3 full-sized toes touching the ground (although Hyracotherium had 4 front toes). Later horses had 3 toes on the ground, but the middle toe did most of the work. The side toes dangled off the ground except during jumping and fast running. Modern horses have only one toe.

To illustrate how the horse foot changed through time, a human hand can be used for comparison. Note how the distance of the wrist bones from the ground changes.

human hands showing wrist and toe comparison

Horse Hooves over Time

Look at how the bones in horse feet have changed over time. They became longer and more streamlined, enabling horses to run faster to avoid predators. The central digit of horses became increasingly stronger while the “side toes” became less important and are virtually lost in the modern horse.

Horse Hooves Progression Diagram
MYA = Millions of Years Ago

Follow this by examining the reduction and loss of metacarpal V (blue) and its digits. Do this likewise for metacarpals II (red) and IV (green). Note that no horse ever had a thumb.

Horse Hooves Progression Diagram - With Highlights

Reduction and loss of side toes minimizes the weight at the extreme end of the foot. This reduces the torque, so the horse’s limb may move faster. Horses are truly “built for speed.”

 

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