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Ask A Vet: Why Do Dogs Have Dewclaws?

We know what our dogs’ feet look like. Most dogs have 5 toes on the front feet and 4 toes on the rear feet.

People may already know that the toes on the side of the front feet that do not touch the ground are called dewclaws, but if they do not touch the ground to help with locomotion, then why are they there at all?

Image Source: Karen.Harris413 via Instagram

 

Of course, dogs are members of the class Mammalia, with humans and many of our other furry friends. Mammalia (from the Latin root word mamma, which means breast) are able to produce milk for their young with their own body using the mammary glands. Dogs also members of the order carnivora (although the name implies that dogs are carnivores, bears and dogs actually belong to the order and are omnivorous). Cats and weasels are also members of this order, but different families.

Both dogs and cats are mammalian and carnivora, but clearly their families split at some point. Scientists think that they diverged up to 47 million years ago1. As you can imagine, many believe that the ancestors of both dogs and cats would have looked and lived very differently than either of the two today.

Back all those millions of years ago, the ancestor of the dog is thought to have been “miacis”. Miacis was small and able to climb. Odds are, his dewclaws were functional in climbing as he would have used them much like we use our thumbs.

Image Source: Karen.Harris413 via Instagram

 

When time altered miacis and allowed him to specialize to his environment, he slowly became more of a ground dweller.  People think that this change forced him to become swifter to evade hunters or hunt for himself. Through selection of the most nimble and gradual survival of the fittest, his foot slowly rocked up onto his toes, allowing him to almost tiptoe rather than having to take time to rock from his heel to his toes, like we do.

The genes that had originally allowed for the thumb still remain, but the dewclaw has become mostly nonfunctional, no longer possessing the muscles and flexibility it once had. The exact details of how dogs came to be the dogs we know and love are debated among scientists. Maybe the dewclaw is just a reminder of how far our dogs have come from the miacis tree dweller to modern day couch dweller!

 

 

 

  1. Tomiya, Susumu. “A New Basal Caniform (Mammalia: Carnivora) from the Middle Eocene of North America and Remarks on the Phylogeny of Early Carnivorans.” Ed. Anjali Goswami.PLoS ONE 9 (2011): e24146. PMC. Web. 6 Mar. 2017.

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