What Is A Cat?

If I say “cat,” you know what animal I mean, though in some settings you might wonder whether it was a house cat or one of the wild species.

Now suppose you’re a paleontologist and you have just discovered one of those natural traps that carnivores and their prey sometimes fall into and can’t get out of. This one goes back millions of years and all that remains now is a messy jumble of bones.

How do you sort out the cats?


Here, kitty, kitty… (Ruth Hartnup, CC BY 2.0)

It’s not exactly easy, but all cats, past or present, do stand out from the carnivore crowd, if you know what to look for.

Experts in ancient life go by very subtle signs but there are also big clues that everybody can see, including these:

  • Cats have short, rather blunt faces
  • Their legs are relatively short, compared to pursuit predators
  • They have retractable claws

The biggest problem for paleontologists after they’ve separated the cats from the “dogs”–actually prehistoric members of the family Canidae, long extinct or still around today–is that all cat skeletons look alike, apart from size.

This is a headache for scientists trying to distinguish between ancient feline species, but it works out for us:

Structurally, [the domestic cat] can be seen as simply a scaled-down model of a lion or a leopard, and in evolutionary terms the larger cats may even be considered as scaled-up versions…[Fluffy] is also a more convenient example to refer to in the comfort of the home when some detail of anatomy or behavior is mentioned.
— Turner and Antón


Trish Hamme, CC BY 2.0

Defining a cat

So a cat–any member of the family Felidae, past or present–is a short-faced carnivore with retractable claws and legs that are long enough to catch food and to pace its territory daily but short enough to support the powerful musculature needed for sudden accelerations, a short chase, and the kill.

Why is a cat’s face shaped that way?

Short answer: The better to bite you.

Details: Cats kill prey with their mouths, more specifically, their upper fangs.

At the final moment of a hunt, a cat goes for the back of its prey’s neck. Muzzle whiskers reflexively stretch forward, finding exactly the right place to insert those fangs in between the cervical vertebrae and sever the spinal cord, which instantly kills the victim.

This killing bite must be powerful–those neck bones sit together fairly tightly.

A cat’s shortened face strengthens its bite for this maneuver.

Think of an animal’s jaw as a lever. The closer its fangs are to the fulcrum, i.e., the jaw joint, the more power they can apply.

So, down through time, cats with shorter faces have had the evolutionary advantage over others, now extinct, that looked more like their long-snouted feliform ancestors and were more likely to fail in a hunt or even get injured by struggling prey.

Cats also have the fewest teeth of any carnivore–basically just the ones needed to process meat–but that probably didn’t influence the shape of a cat’s face as much as basic jaw mechanics did.


Tambako the Jaguar, CC BY-ND 2.0

Why do cats have retractable claws?

Short answer: The better to grapple you.

More information: A cat’s claws grow out of its “finger” and “toe” bones just like our nails do, and they are made out of the same material. There the resemblance ends.

Primates developed flat nails to help them grasp things like branches. Some other tree-dwellers–basically most mammals right after the K/T extinction–had claws, which are terrific for holding onto bark, no matter what your diet.

When mammals finally moved down to the ground (which has a lot more surface area than tree limbs), a group turned their “nails” into hoofs.

Not all of these early hoofers were vegetarians.

Mesonychids were rather wolf-like primitive carnivores with a little hoof on each toe instead of a claw! However, as time passed they disappeared and all predators had claws.

That’s an old story, but one that cats and most other feliforms have improved upon.


Nirmal KF, CC BY-SA 2.0

See how this annoyed kitty has its digits spread out?

Spreading your digits is a natural motion when reaching for something like prey (or an irritating photographer). It unsheathes the claws when cats grab prey at the end of a hunt. (Yes, they also do it intentionally sometimes, like this cat; they can even show subtle shades of annoyance this way, as every cat owner soon learns.)

Here’s how it works.  You may have noticed that a cat’s paw look shorter and rounder than a human hand, even though we have the same bones.  (Cats and people shared an ancestor many tens of millions of years ago.)

That’s because, when the cat is just hanging out or walking around, strong ligaments hold each claw and the bone it’s attached to alongside the second bone instead of end-to-end, like in primates.

Spreading out the paw, shown above, makes the ligaments extend the claw and tip bone, and Kitty is locked and loaded. Bring the digits together again, and the whole arrangement retracts back into its resting position.

Why does leg length matter?

Short answer: The better to stalk and ambush you.

More information: Like most animals, carnivores have to move around to make a living. Each has its own style, but they do mix it up a bit.

Bears, for instance, are ambulatory predators, like terrestrial raccoons, so they generally just shuffle along. But as somone once said, people have ended their lives being surprised by how fast a bear can run.

Cats climb almost as well as palm civets, but they’re not arboreal predators. The feline evolutionary path took cats to the zone where open land and forests meet. Here cats became stalk-and-ambush ground hunters (though some people probably have ended their lives surprised that big cats are so agile in trees).


The human environment has a similar blend of climbable things and open areas, but we only tolerate house cats in it. (Doanme at Pixabay, public domain)

A cat’s legs are proportionally longer than a bear’s because the cat needs to run more, as well as cover a lot of ground on its daily territory patrol. However, dogs have longer legs than cats because they chase their prey long distances instead of ambushing it.

Cats have evolved into a happy medium. Their legs are long enough for good acceleration and speed over short distances but not so short that the bone would snap under forces generated by powerful muscles needed for stalking and hunting.

Speaking of locomotion, of course this post closes with a cheetah video!

Cheetahs are extreme, but this excellent video does show what we’ve talked about (including retractable claws, sort of) and more of the sleek features that all cats, including Fluffy, have evolved, including (but not limited to) shoulder blades and clavicles designed to speed them on their way; all four legs underneath the body to conserve inertia; the knee joint next to the pelvis (can you do that while running?); and the head relatively immobile and focused on the moving prey.

Featured image: Marina del Castell, CC BY 2.0

Biknevicius, A. R. and Van Valkenburgh, B. 1996. Design for killing: craniodental adaptations of predators. Carnivore Behavior, Ecology, and Evolution, 2: 393-428.

Rose, K. D. 2006. The Beginning of the Age of Mammals. Baltimore: The Johns Hopkins University Press.

Martin, L. D. 1989. Fossil history of the terrestrial Carnivora, in Carnivore Behavior, Ecology, and Evolution, ed. Gittleman, J. L., 536-568. Ithaca, NY: Cornell University Press.

Taylor, M. E. 1989. Locomotor adaptations by carnivores, in Carnivore Behavior, Ecology, and Evolution, ed, Gittleman, J. L., 382-409. Ithaca, NY: Cornell University Press.

Turner, A., and Antón, M. 1997. The Big Cats and Their Fossil Relatives: An Illustrated Guide to Their Evolution and Natural History. New York: Columbia University Press.

Werdelin, L. 1989. Carnivoran ecomorphology: A phylogenetic perspective, in Carnivore Behavior, Ecology, and Evolution, ed. Gittleman, J. L., 582-624. Ithaca, NY: Cornell University Press.

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