Dog Paw Anatomy, Bones & Evolution

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Grey’s Anatomy is not the only anatomy you should be digging into. If your best friend has four paws, you should know them like the back of your hand. If you think about it, they traverse the world barefoot almost at all times. Stepping on hot concrete, icy pavement, or rocky hill, you name it, is far from comfortable.

However, while people take a great deal of decision-making when picking the proper footwear, they not so often think about their dog‘s paws‘ well-being. What do your dog’s paws consist of, and why are they so resilient against the ever-changing environment? Moreover, how did they even develop?
 

Anatomy

To get a basic understanding of the canine paw, you must know that it essentially consists of 5 parts:

  • Claws could be canine equivalent to nails. They are located at the end of the dog’s toes and have multiple crucial purposes. They both provide the dog with stability when standing and security by enabling him to defend. Moreover, toenails create traction necessary for digging holes or tearing up their prey.
  • Dewclaw, on the other hand, could be considered a dog’s thumb. You can find it more to the side and slightly away from the central part of the canine paw. Dewclaw is primarily present in front paws but rarely can appear in rear ones as well. Some breeds as Australian shepherd or rottweiler have double dewclaw; these are then known as polydactyl. It doesn’t usually touch the ground; however, dogs running at high speeds use them for extra traction to better stabilize the carpal joint. Some dogs even use it when climbing or holding objects. Dewclaws are not present in all dog breeds and are sometimes removed in puppies to prevent infection. Such procedure is usually taken only if the dewclaw is loosely attached.
  • Digital pads are probably the most known part of a canine paw. Dogs have 4 digital pads in total, one at each toe. They are hairless; however, pieces of fur may get in between toes. Digital pad is a thin, pigmented, and keratinized layer of skin covering tissues of collagen and fat. Thanks to the layer of fat underneath the skin, digital pads are shock-absorbing, protecting the canine joints and bones from irritation due to unpredictable or rough terrains. However, the purpose of digital pads goes beyond being the shock absorber. They not only provide a better grip on any surface but also reduce the heat transfer between the dog’s body and the surface underneath, keeping the dog warm even in colder temperatures.
  • The metacarpal/metatarsal pad has a heart shape and is located in the middle of a paw. While the metacarpal pad is on the front foot, the metatarsal pad is on the rear one. They are both shock-absorbing and load-bearing parts of the paw. Their function is overall very similar to the purpose of digital pads.
  • A Carpal pad is the furthest part of a paw from claws and can be mainly found on the forelimb, yet some dogs may have it on the rear feet as well. Their structure is similar to the metacarpal pad. They often come in handy as they act like a dog’s emergency brake. Suddenly stopping on a slope or a slippery terrain requires additional traction provided by carpal pads. However, the same applies if a dog chooses to stop quickly in tight spaces. Their structure also allows them to absorb shocks, and therefore protect joints when jumping. Lastly, the carpal pad helps a dog maintain control even at high speeds, acting as a means of achieving balance.

dog paw anatomy in detail illustration
 

Bones

To understand how the canine paw functions at an even deeper level, let’s take a look at its bones structure.

  • Phalanges form the digits of the foot. There are three phalanges per toe, except for the first digit, the dewclaw. This could be compared to a human thumb and comprises of only two phalanges. The three phalanges are distal, middle, and proximal. The proximal phalanx is connected to the metacarpal/metatarsal bone to which we’ll get in a minute. The middle phalanx lies between the proximal and distal ones. Finally, the claw is attached to the distal phalanx. Dogs have 4 toes per paw, excluding the dewclaws.
  • Metacarpal/metatarsal bones connect to both phalanges and carpal/tarsal bones. As was the case of canine pads, metacarpal bones are present in the forelimb and metatarsal in the rear paw. As humans, our four-legged friends have 5 metacarpal bones. On the other hand, they, unlike us, have only 4 metatarsal bones.
  • Carpal/tarsal bones are the equivalent of human wrist or ankle, respectively. They are 7 bones connected by various ligaments, creating a very firm surface that can withstand shocks. The whole joint is then called a carpus/tarsus. The bones are arranged into 3 irregular rows, with an accessory carpal bone being the fourth row.

 

Evolution

However, many years had passed before the canine paw developed into a well-known form. To search the origin of canine genealogy, we have to go back approximately 60 million years. Back then, a carnivorous mammal Miacis laid the foundation for the appearance of the modern dog. Nonetheless, you would be surprised to find out that Miacis looked like a weasel, was only as big as 30 cm (11.5 inches) and walked on its soles instead of toes. It has taken 25 million years of development to reach the next significant stage, the genus Leptocyon.

Miacis illustration and its paw evolution
Miacis

This genus is considered the first canine, yet the mammal still resembled a fox rather than a dog. Leptocyon already used toes for walking, slowly moving towards characterizing the modern dog. Around 20 million years ago, Mesocyon came, bearing the resemblance of a basic dog and having a more developed brain. Thanks to an increased intelligence and memory span, members of the Mesocyon family developed a pack mentality as they know could remember their own. If you’re now saying that these mammals seem to behave like wolves, you wouldn’t be far from the truth. Mesocyon was indeed followed by the wolves “just” 5-7 million years ago. These already walked on hind toes.

It was only 33,000 years ago that humans started domesticating some members of wolf species. The process of selective breeding enabled us to breed dogs for specific tasks. However, it has taken its toll on dogs’ health as detrimental genetic mutations were passed along with desired physical or behavioral traits. Despite the early existence of different dog breeds, many others were created by selective breeding. This accounts for the vast differences between modern dog breeds.

As was already mentioned, Miacis walked on soles while the modern dog uses its hind toes. Why was this change necessary? Moreover, why does the canine paw have only 4 toes, unlike humans? These questions might deliver the most essential information of the day. However, they may randomly pop into your mind, bug you before falling asleep or simply come in handy when a family conversation stalls.

Humans have five relatively long fingers to grasp and manipulate objects. Dogs, on the other hand, predominantly need their palms and feet for walking or running. Cursorial animals which need to maintain high speeds for long distances developed long limbs but shortened digits and fewer toes. Long limbs allow dogs to run speedily. When humans run, they roll their feet from heel to their toes. This process is lengthy, and thus, Leptocyon had already been using for running only its toes.

Lastly, the reason why dogs have only 4 toes is probably to lose excessive weight slowing the dog down. While the additional weight from having 5 toes is not that big, it can make a difference in such a small animal, especially over a prolonged period of running. On the other hand, the evolution of canine species introduced the dewclaw, a fifth digit providing an emergency break.

So, after all, the canine paw evolution is all about making the energy distribution during running more efficient!
 
dog efficient running with fully developed paws