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Why do cats have an extra toe on their front paws?
Question Date: 2016-08-31
Answer 1:

As you know, cats usually have 5 toes on their front paws and 4 on their back paws. Having 5 toes is actually the normal number for most animals with backbones and 4 legs. There are exceptions, of course. Way back when the first 4-legged animals were evolving, 5 toes seemed to become the normal number. It happened about the same time as the complicated wrist bones evolved. Most of the species that evolved from those early 4-legged critters have 5 toes. 5 toes are not necessarily better for most species, that’s just what we have because our ancestors had them. Primates like us use our thumbs a lot, but it may not be too important for other animals.

The more interesting question might be why they have only 4 in back, when 5 is so much more common. When I think of a question like this, I look for patterns. Which species have lost toes? Why?

Well, horses have lost all but their middle digit. Their hoof is basically a fingernail that is very big and thick. If we look at fossils of their ancestors, we can see that the earliest ones had 5 toes. They walked and ran on their fingers and toes like cats, not on the bottoms of their feet like bears and humans. Later horse ancestors ones had fewer toes. In modern horses, there are the remains of 2 side toes that help to form a joint, but only one full toe left. They run only on the tip of one toe instead of on their toes like dogs and cats.

see picture here "The evolution of the Horse"

Why would they lose the side toes? Well, a single hoof makes their foot lighter, which is an important thing for an animal that specializes in speed. They lost the ability to grab things or turn their hands and feet to the side.

So, maybe cats with only 4 back toes are able to run faster than cats with a full set of toes. Having 5 front toes can still be helpful for grabbing prey, climbing trees, or slashing. That 5th toe is where a thumb would be if they were primates. It’s called a dew claw. On some cats it’s actually big, like a thumb. On others, it’s smaller and higher up.

Some cats have extra toes. This is caused by a dominant gene, meaning that they can have extra toes even if they only get that gene from one parent. It’s also a kind of gene that can have a stronger or weaker effect in different individuals. So, some cats with the gene may have a tiny extra claw, while others can have a couple of extra full-sized toes on each paw. Some even have different numbers of toes on different front paws or back paws. We recently fostered a litter of kittens that had all different numbers of toes. Some had the usual number. Others had an extra toe. Others looked like they had catcher’s mitts for paws.

Why do you think bears and raccoons walk on flat feet when foxes and bobcats are up on their toes?

If you are interested in questions like this, you may want to study anatomy, evolution, or genetics.

Thanks for asking,

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