Part of the Family: Housecats

This is a continuation of my blog series, Part of the Family.

So now that we understand how humans are related to other primates, going all the way back to before the asteroid impact 65 million years ago, it's time to figure out how our pet cats figure into this family equation. Like my best buddy, Galileo:

We adore them, pamper them, and love them. Some of us do all of that while sneezing our faces off. But why? What's so stinkin' cute about a widdle puddy tat?

Well, first off all...ever notice how humans are much more likely to find other mammals cute, rather than say, a bird, or a snake, or a lizard, or a frog? Sure, some of us just find everything adorable, but the average person is going to be way more warm-fuzzied by something that is, well, warm and fuzzy.

And that makes sense. We tend to feel most protective towards creatures that share more of our genes. Why? Because we're programmed to feel that way. By our genes. (Is your mind blown yet?)

We share the vast majority of our genes with the common domestic cat, just as we do with any mammal. But cats (and dogs for that matter) are not the most closely related mammal to primates. Regardless of our personal feelings, as a human, you're more closely related to a rat than you are to your precious Mr. Mittens McFluffytail. Can't pick your relatives, right?*

So if we should feel more protective towards things we're more closely related to, why do most people prefer cats to rats? Obviously, things are much more complicated than simply ranking your favorite creatures by the percentage of DNA you share. Cats have wormed their way into our hearts, beating out our closer rat relatives, by improving the odds of our human relatives' survival (which totally trumps everything else). So good job, cats. You've essentially beaten the system.

Our relationship with cats has slowly developed over time to be one of mutual assistance. They help us keep our food safe from rodents, we in turn protect them from predators and ensure they don't starve.

Cat with kitten amulet, 400 BC

Mummy cat, 400-200 BC

This has been going on for a long time. At the very least, from the time of the ancient Egyptians 3600 years ago, as evident by paintings of house cats, statues of cats in homes, and the mummification of cats as respected, even revered, creatures.

There is evidence that this relationship with cats may predate the ancient Egyptians. In a burial dated to 9500 years ago from Cyprus, a human was found carefully laid to rest with a cat.**

 Whatever the case, we've been hanging with cats for millenia. That's long enough that the cat may have actually influenced the past few thousand years of human evolution. It could be that we've had a slow selection acting on us to favor people who like, or at least tolerate, cats milling about in their lives. They're helpful, after all. It would not surprise me to learn that we have a collection of genes that effectively give us "cat tolerance".

But beyond our current social relationship with cats, what about our genetic one? How to felines actually relate to primates?

Sand cat.

Well, it's time to go backwards through time yet again.


The modern domestic cat is part of the genus Felis, which includes several species of small cats such as the sand cat of northern Africa and the Middle East.

African Wild Cat.

This genus of cats is mostly known for its smaller size and its affinity for hunting rodents. They split off from the rest of the cat family around 10-8 million years ago, according to genetic studies. The African Wild Cat is likely the particular member of this genus that gave rise to our own fluffy household kitty cats.

Before 10 million years ago, these cats would've been part of a larger group called the subfamily Felinae, which again, is mostly small cats, but does include the ancestors to the cheetah and the cougar. So if you've ever wondered which big wild cats your pet is most closely related to, there you go.

Creepy thought of the day: the Cheshire Cat must eat meat to survive.

All members of the Felinae subfamily are part of a much bigger family known as the Felidae, or simply, the cats. The cats branched away to do their own thing around 25 million years ago. So what sets them apart from other animals? Retractable claws. Five toes on their front paws, four on their back. Their characteristic "sandpaper" tongue, used to rasp meat off bone. Fewer teeth than other carnivores. Being carnivores. And not just regular carnivores, but obligate carnivores. That means they must eat meat to survive, and very little (if any) of their diet is based off of non-animal material. They are the most carnivorous of any land carnivore. So it may not come as a surprise to learn that they're part of a bigger animal order called Carnivora.

Carnivora is an order that's broken up into two suborders, the feliforms and the caniforms. Guess which one your cat is from? Yep, the suborder Feliformia. Guess which one dogs are from? Duh, Caniformia. Now guess which one those nasty Lion King hyenas were from?

Feliformia. Yep. Hyenas are more closely related to cats than to dogs.

Anyhow, the two suborders split around 42 million years ago. One major distinguisher between the two is how their auditory bulla (or ear bone covering) is formed. Feliforms have a double-chambered one, caniforms have a single-chambered one. Might not sound fascinating, but its these sorts of differences that are key for paleontologists, who work with bones. Other differences include the behavior of feliforms to be more ambush-y in their hunting strategy than caniforms, but that's a lot harder to tell from the bones.

Sadly, another difference is that feliforms are usually more forest-based, so that means we have a terrible fossil record for them. Bones degrade quickly in forest environments are rarely have time to fossilize.

So onwards (or backwards) to the next big split: the Carnivora from the rest of the Eutherians (non-marsupial mammals). This is finally where we'll see what drove apart cats from humans!

There is no such thing as a saber-toothed tiger.

Carnassials!

Carnivorans are characterized by a pair of humungous gnashy-gnashy meat-destroying teeth on each side of their jaw, known as their carnassials. Carnassials are not to be confused with saber-teeth, which did show up in some Carnivores, like the saber-toothed cat, Smilodon. Carnassial teeth are farther back and meant for ripping meat and crushing bone open for marrow, and not so much for the actual killing of prey.

So now we're almost to the point where our cats lineage joins up with our own. Carnivora branched off before 65 million years ago. But even earlier in time that, there is one last branching event to talk about. The branch that separated one major group of mammals from another, long before the infamous asteroid struck Earth and cleared the way for mammals to take over.

On one side of this branch are the carnivores, the camels, pigs, goats, giraffes, the whales, the horses and the rhinos, the shrews, and the hedgehogs, among many others.

The other side includes the rabbits, the rodents, and the primates. In other words, us.

Major split. And probably happened over 90 million years ago. The only physical characteristics that tell these groups apart may be some features of the skull around the ear. The split itself was probably just an element of location. The group the cats belonged to came from the supercontinent, Laurasia, while our group seemed to originate from islands off the coast of this supercontinent.

So some 90-odd million years ago, the last common ancestor of cats and humans had one of its members swept up and out to sea to land on some islands near the coastline. Our last common ancestor would've looked quite a bit different from either of us, but would've had a few recognizable features. It would've had hair on its body. It would've had teeth that came in the form of molars, premolars, canines, and incisors. And it would've given birth to live young, attached via a placenta, which it then would have nursed with milk.

Above is an artist rendition of Eomaia, 125 million years-old, and one of the early ancestors of humans and cats alike. Maybe she doesn't look like much, but she gave rise to a really cool batch of animals.

Now, maybe you're saying to yourself...wow. This was a lot to read. It sure took a while to get to the point back in time where humans and cats really were one and the same. We're not that closely related, after all!

If that is indeed what you're thinking...just wait until you see how we're related to the ground up coffee beans used in your morning latte.



* I adore rats, for the record. And they will be the focus of a future "Part of the Family" blog post.

** I am not an archaeologist, and do not know if this discovery is controversial within the field or generally accepted as an actual indication of early cat domestication. If anyone more informed does know, please chime in!


Citations:

Benton MJ. 2005. Vertebrate Paleontology: Third Edition. Malden, Massachusetts: Blackwell Publishing Ltd.

Johnson W.E., Eizirik E., Pecon-Slattery J., Murphy W.J., Antunes A., Teeling E. & O'Brien S.J. 2006. The Late Miocene radiation of modern Felidae: A genetic assessment. Science 311: 73–77.

Pecon-Slattery J. and O'Brien S.J. 1998. Patterns of Y and X chromosome DNA sequence divergence during the Felidae radiation. Genetics 148: 1245–1255. 

Prothero DR. 2004. Bringing Fossils to Life: An Introduction to Paleobiology: Second Edition. New York, NY: McGraw-Hill.

Blog Series: Part of the Family

Here's something I've been wanting to do for a while. It's time to explain to the interwebs how I see the world. This will be the introduction to a series of posts discussing why I consider everything on Earth to be part of my family.

Starting with this guy:

Yes, that is my cat. His name is Galileo. And he's four years-old.

He's also part of my family.

Now...many people say that about their pets. And they mean that they love them as if they were actually a "related" person.

But your pets are related to you. Everything is. In this post series, I will aim to expand minds to see what exactly our relationship is with everything around us. We're all part of a tremendously huge story. Characters in an ongoing saga, if you will. An ongoing saga of awesome.

In order to understand how we're connected to everything else, it's critical that we start out with an understanding of the last 55-80ish million years of human evolution. This will allow us to see how humans connect with the rest of the mammal world.

A rough idea of evolution over the past 2 million years. 

Humans as Homo sapiens have been around for oh, about 200,000 years now. Just a sliver of time when you consider the over 14 billion year history of our universe.

Instead of a giant prehistory lesson, I'll skip over many of the various species names involved in human evolution (since many of the designations are hotly debated anyway) and just discuss the broad changes that occurred. If you're really curious, I've included a basic visual for the past 2 million years. (For those counting, I said we're going to cover nearly 80 million years of evolution. Just keep that in mind.)

Modern humans came about as a change of brain structure, mostly. Going backwards, the genus Homo as a whole came about from some brain restructuring, but honestly mostly just from our ancestors getting longer legs. This was just over 2 million years ago.

Who's that good lookin' gal?

Before that, we were shorter and had more body hair and smaller brains. This was the time of the australopithecines. If we saw an australopithecine today, we'd probably be more tempted to call it a weird-looking chimpanzee. Why? Because they are much closer to the common ancestor of humans and chimps than we are!

We split from the line to chimpanzees around 6-7 million years ago. Roughly. At the split, human ancestors adopted more of a bipedal locomotion style, while chimpanzee ancestors either retained or developed a knuckle-walking locomotion style. This was probably due to filling in different environmental niches. This whole period of time is still pretty fuzzy, though. We used to think human ancestors evolved for life in the grasslands, but that's probably not the full reality.

In any case, it's important to remember that WE DID NOT EVOLVE FROM CHIMPANZEES. That'd be like saying your cousin gave birth to you. No. That's not how it works. We share a common ancestor with chimpanzees, but chimpanzees have been evolving away from that common ancestor just as much as we humans have been!

Swinging along like a champ. Ape pride!

Now before our split with chimpanzees, we were part of a species that went on to produce us, chimps, and gorillas. The African Ape gang. But if you keep going back in time, our ancestral species 14 million years ago also branched off to produce orangutans. And before that, 18 million years ago our ancestors split off a branch that went on to produce gibbons.

But before 20 million years ago, things get fuzzy again. We know from genetic testing that apes and monkeys (that's right folks, apes are NOT monkeys) split around 30 million years ago, but the fossil record kind of stinks for a while here. We don't know exactly what we looked like during this time, but we do know what makes apes distinct from monkeys. The loss of the tail, for instance. Extra mobility in the limbs (monkeys, for the most part, can't do monkey bars, while humans, being apes, rock the socks off monkey bars). All of that came about during this time frame, from around 34-18 million years ago.

But before that, we were one and the same with the monkeys. We were not monkeys, just as we were never chimps. We were part of a group that included the ancestors of modern monkeys and apes called haplorhines. (For the nerdy among us wondering, I'm skipping over the division of catarrhines from platyrrhines 40 million years ago and going directly to our common ancestor for all monkeys and apes. Because talking about losing an premolar in the dental formula is just not that fascinating to the average person.)

A kitty cat's split lip.

Haplorhines split from a group called strepsirrhines (which include lemurs, lorises, and galagos) between 60-65 million years ago. Haplorhines are the "dry nosed primates". That means our nose doesn't have that split down to the lip that many other mammals have. Strepsirrhines keep that split. Their mouth and nose looks much more like that of a housecat.

Smilodectes, roughly 50 mya.

Now, the ancestor of all primates, haplorhines (monkeys, apes, tarsiers) and strepsirrhines (lemurs, lorises, pottos, galagos) alike, may have already been around as early as 85 million years ago, according to some recent molecular clock data. Even if it wasn't 85 million years, it had to be before 65 million years ago, based on genetic evidence. So for those doing the mental calculation...primates split from the rest of mammals a long, long time ago. And yes, primates survived the asteroid impact 65 million years ago.

Unfortunately, the fossil record for primates before 58 million years ago is poor, so it's hard to say exactly when our first primate-y features showed up, or even what they were. But from the record we do have, it seems the earliest true primates had an increased reliance on vision, and greater finger/toe dexterity with opposable big toes or thumbs. The rest...well, paleontologists are still trying to figure out the rest.

So there you have it. That's us. All the way back to our split with the rest of Mammalia.

Which means we can now trace our relationship to other mammals...like my kitty cat, Galileo. But that will be for a future post. This post was just an introduction to the amazing story that connects us all. We'll need to dive deeper to see how we're related to everything else around us.



Citations:

Chatterjee HJ, Ho SYW, Barnes I, Groves C. 2009. Estimating the phylogeny and divergence times of primates using a supermatrix approach. BMC Evolutionary Biology 9: 259.

Fleagle JG. 1999. Primate Adaptation and Evolution: Second Edition. San Diego, California: Elsevier. 

Ward CV, Begun DR, Rose MD. 1997. Function, Phylogeny, and Fossils: Miocene Hominoid Evolution and Adaptations. New York: Plenum Press. New York: Plenum Press. p 1-12.

RIP Maurice Sendak

“And [he] sailed back over a year
and in and out of weeks
and through a day
and into the night of his very own room
where he found his supper waiting for him
and it was still hot”