The evolution of cats?
As far as I’m concerned, Life, the Universe, and Everything appeared just so this young lion could get that much satisfaction from a green rubber ball. You’re welcome, Leo.
We’re done here . . .
Wait. Why pass up such a fascinating topic?
It may take a PhD to cover every detail of where cats come from and where they might be going, but some of the most interesting highlights aren’t at all hard to understand.
Let’s check out ten common misconceptions about fossil cats and how they turned into the modern cat family Felidae.
To start off, most people think that . . .
10. Dogs and cats are unrelated.
Cats and dogs work hard to keep this misconception going, but they’re actually “kissing cousins.” Well, sort of.
Not much hard evidence of the carnivoran family tree has survived the last sixty-six million years of geologic activity, but paleontologists still comb through fossil beds, searching for the last common ancestor of dogs and cats.
There must have been a hungry little mammal – they were all little back then (Rose) – that either survived the K/T extinction or developed very soon afterwards, during the first epoch of the Age of Mammals – the Paleocene. (Benton and others, page 66; Fox and others; Nyakatura and Bininda-Emonds, 2012)
How do the boffins know that?
From cat and dog teeth, specifically, certain upper and lower cheek teeth that fit together like scissors blades.
They’re called carnassials, after the French word for “carnivorous.”
Carnassials are why Fluffy rarely takes food from your hand. The cat has to use its cheek teeth on food.
Its impressive fangs and incisors are specialized murder tools, as we’ll see in #6 later.
As you can see, cats and dogs aren’t the only ones with carnassials. All members of the biological order Carnivora have them. (Revell)
It’s always the same teeth, too – the last premolar on the upper jaw and the first molar on the lower jaw. (University of California Museum of Paleontology)
This means that all carnivorans inherited their carnassials from the same ancestor.
That’s the K/T-surviving and/or fast-evolving animal paleontologists would love to identify in the geologic record.
Now, the next misconception is something that every zoo visitor and safari adventurer takes for granted. Scientists once thought it was true, too.
9. Hyenas and the big cats are unrelated.
Not surprisingly, wildlife biologists used to classify hyenas as caniforms. (World Heritage Encyclopedia) That’s science-speak for “dog-like.”
Today’s caniforms include (but aren’t limited to) dogs, wolves, foxes, skunks, bears, weasels, badgers, wolverines, raccoons, and . . . walruses?
Yes, and otters and seals, too. Not killer whales, though. (Heske)
Hyenas were moved out of the group when genetic testing showed that they are really feliforms, though it isn’t clear exactly how they fit in with the rest of the “cat-like” carnivorans. (Barycka)
Feliforms include families you don’t usually think of as related to cats until you see them all together. Here are modern representatives of the whole feliform group (Heske):
OK, the hyena still seems strange there, but molecular analyses don’t lie.
By the way, meerkatts are in the mongoose family. They are smart, but cheetahs are smarter.
Since paleontologists are still looking for the last common ancestor of dogs and cats, you probably won’t be surprised to hear that no one knows for sure when these two groups went their separate ways.
The oldest known caniform and feliform fossils go back to the Eocene – the second epoch of the Age of Mammals. However, molecular studies suggest that the big break may have happened long before then. (Benton and others; Nyakatura and Bininda-Emonds, 2012; University of Edinburgh)
The exact date hasn’t been pinned down yet. Some researchers think . . . Uh-oh. Let’s move on – something really horrible has just appeared in the tree branches over your head . . . act casual and don’t turn your back on it.
8. All fossil cats are sabertooths.
There are more sabertoothed cat fossils overall (Werdelin and others), and they are certainly eye-catching, but “normal” fossil cats are impressive, too.
In addition to a host of mysterious little felines that lived in North America and China around 6 to 8 Ma (million years ago), these fossils include the ancestors of many modern cat groups. (Werdelin and others)
Exact dates are controversial, but the oldest “normal”-toothed cat fossils certainly go back more than four million years (Felis and perhaps some big cats); the youngest are less than 500,000 years old (jaguarundi). (Eizirik and others; Geraads and Peigné; Luo and others; Tseng and others; Wang and others; Werdelin and others; Werdelin and Dehghani)
For comparison, the oldest known sabertoothed cat fossils are roughly eleven million years old. (Antón)
Of course, it’s easy to identify sabercat fossils by their saberteeth . . . right?
7. Saberteeth mark the difference between modern and sabertoothed cats.
How can this be a misperception? Sabercats have saberteeth and modern cats don’t.
Well, that’s true as far as it goes, but maybe it isn’t the whole story.
Experts are starting to suspect that small lower fangs are the key sabertooth feature, not the big ones displayed by the clouded leopard in the following video, as well as other “normal”-toothed cats.
Paleontologists have always sorted sabertooths by the shape of their upper canine saberteeth. In the twentieth century, they started subdividing these cats into dirk-tooths and scimitar-tooths. (Martin, 1980)
The knife-like sabers in two of those three skulls up above are dirk-tooths. (“Knife-tooth” was already taken; that’s what the name for the whole sabercat group – “Machairodontinae” – means.)
All this cutlery talk is a little misleading.
Saberteeth aren’t really like a knife or sword because their cutting edge is on the inside curve (Martin, 1980), but scientists use these terms for the very obvious dental difference between these two sabertooth lines.
The dirk-tooth/scimitar-tooth system works very well for Smilodon and Homotherium, but they weren’t the only sabertoothed cats.
The very first sabercats appeared in the fossil record around 12 Ma (million years ago), back in the Miocene epoch. (Agustí and Antón)
They actually were built more like modern cats than the ice-age sabertooths that would follow them. (Antón)
And some of them were huge.
What did the gigantic owner of these sabercat bones – “Machairodus aphanistus” – look like? See one expert’s reconstruction of it at the bottom of this blog post. The smaller Miocene cat used for comparison only comes up to Mach-A’s midleg, although it was bigger than a modern housecat – somewhere between a wildcat (a little over a foot high at the shoulder) and a serval (up to two feet tall) in size. (Salesa and others, 2012)
They may have been primitive, but those early sabercats were impressive!
Their saberteeth weren’t all that prominent, though. And just to make things as complicated as possible for paleontologists, each of their sabertooth characteristics evolved at a different rate from the rest – a process called “mosaic evolution.” (Antón)
Controversy swirls around a few Miocene cats, like Metailurus and Dinofelis, who both combined sabercat and feline features. (Antón; Werdelin and Lewis)
Such variations don’t fit very well into the dirk-tooth/scimitar-tooth system. However, the proposed new sabercat sorting system has room for them alongside the sabertooth regulars.
Supporters of this system have noticed another outstanding difference between sabertoothed and modern cats.
You can see it, too, in that image of the lion skull and two sabercats shown earlier.
Of those three skulls, the lion has the biggest lower canines (fangs).
And this is one tooth size contest where modern cats usually beat the sabertooths.
Some experts have classified sabertooths, using the lower canines and a few other dental features, not the famous upper canines. (Christiansen)
They found that the two ice-age tribes, Smilodon and Homotherium, plus some other recent long-tooths all fall into one natural group – these are truly sabertooths. All the earlier sabercats and controversial Miocene cats fit into another natural group. (Christiansen)
It’s quite a change, and paleontologists are still looking it over. But this does appear to be another valid way to explain how sabertoothed cats evolved.
Which approach is the best? We’ll only know for sure when experts finally figure out how the sabercats used their impressive teeth.
What’s that? You thought that . . .
6. Cats used their saberteeth to stab prey and bleed it to death.
There’s no question about the bloodletting, but no one really knows how sabertoothed cats achieved it.
It couldn’t have been like modern cats, who dispatch small prey with a killing bite to the back of the neck. Their fangs slip in and dislocate the cervical bones. (Kitchener and others, 2010)
The presenter in that clouded-leopard video earlier must have been aware of this as the cat settled down on the back of his neck. He handled it with true British aplomb (and probably several animal handlers just off camera).
Saberteeth would break in such a bite. Modern cats have cone-shaped upper canines that can take the stress. (Kitchener and others, 2010)
And stabbing doesn’t work very well. It also can be very costly, as we will see in the final list item.
When sabercat fossils first came to light, many paleontologists thought that animals had specialized their way into extinction.
[T]he huge canines in the “Smilodons” must have . . . greatly interfere[d] with feeding and [kept] the animals in poor condition.
– Edward Drinker Cope, 1880
But as we will see shortly, sabercats were actually the fourth group of placental mammals to develop saberteeth since the K/T extinction.
As a paleontologist whose name I cannot remember once wrote, sabertooths starved to death for almost forty million years?
That’s not failure; it’s a big success story. (van den Hoek Ostende and others)
Obviously there are excellent advantages to having long, flattened upper canines.
But we don’t know what they are. No record of the sabercat hunting style has come down to us.
Humans were around during the ice ages, but the cave drawings found so far don’t show sabertooths.
We must use our imagination in lieu of any historical record.
And here is a video that may be as close to a real-life sabertooth hunt as you’re likely to get these days.
Some of that was based on the BBC’s “Walking With Beasts” sabertooth episode, but the Beeb has a different idea of how Smilodon looked and moved.
Not only does their Smilodon move like a lion, the animators also assume that this sabercat was as social as lions. That’s not impossible, but it hasn’t been proven yet (see Antón, Chapter 4, “The Social Life of Sabertooths”).
Here, the narrator describes the effect of the canine shear bite Smilodon and other sabertooths might have used to kill prey:
“One bite and the prey is dead.” Indeed.
Paleontologists suspect that the major advantage to saberteeth was a quicker kill through massive blood loss and suffocation. (Turner and others)
Why hurry? While no modern predator would likely survive a confrontation with a healthy, young Smilodon, back in the day there were other big predators around that the sabercat had to fight off, risking damage to its saberteeth. (Agustí and Antón; Prothero)
There were dire wolves, other cats, various scavengers . . . and humans.
At La Brea, competition must have been fierce. Not just sabertooths, but also dire wolves, coyotes, and “normal”-toothed cats predators there broke their teeth up to three times as often as modern carnivores do. (Van Valkenburgh and Hertel)
The sabertooth advantage isn’t limited by time or geography. Down through the Age of Mammals, sabertooths have roamed all the continents except Australia. (Antón) Fast food is always a good idea in the wild.
But not all of those sabertooths were cats . . .
5. All sabertooth fossils are cats.
It surprises many of us to hear that there was more than one kind of sabertoothed cat during the ice age – the Homotherium tribe, as well as at least two Smilodon species.
And few realize that, as we saw in #7, sabertoothed cats were also around millions of years before those continent-sized ice sheets first started to grow.
But almost no one outside the paleontology department is aware that all of these toothy cats were actually Sabertooth v4.
Among placental mammals, there have been three sabertoothed lines besides the sabercats. Two of those were very cat-like. (Antón)
Version 1 wasn’t.
It was just a couple of primitive sabertoothed creodonts – Machaeroides and Apataelurus – who lived in North America around 40 to 55 Ma (million years ago), during the early to middle Eocene. (Antón)
These two may have been the first sabertoothed mammals, but they set no trends. The other creodonts stayed with traditional teeth and outlived Machae and Apat, who were both extinct by the time Sabertooth v2.0 appeared. (Antón)
Nimravids possibly originated in Asia (Averianov and others), but they first showed up in North America’s fossil record during the late Eocene – around 37 Ma. (Antón; Bryant; Peigné; Werdelin and others)
They were already cat-like. Unfortunately, no one knows how that beautiful feline shape first evolved. (Werdelin and others)
Nimravids may have been the first feliforms (Benton and others) or possibly a very early carnivoran group that developed before the dog-cat split. (Werdelin and others)
Even though nimravids had cat-shaped skulls, cat-like dental adaptations to a high-meat diet, and retractable claws, not to mention saberteeth (Bryant), they also had some caniform features. (Bryant; Flynn and Galiano)
This means that nimravids might have developed before feliforms and caniforms went their separate ways.
In any event, millions years after the world’s last nimravid died, Sabertooth v3.0 showed up in Africa around 19-20 Ma and spread across Eurasia and North America. (Antón; Werdelin and others)
These were the barbourofelids. This group included some of the most extreme sabertooths known.
Like nimravids, barbourofelids were very cat-like, but many paleontologists believe that they weren’t nimravids. Their possible connections to the cat family are uncertain. (Antón; Werdelin and others)
Whoever drew this Carnivora phylogeny tree thought that barbourofelids were related to the cat family, but it’s just as possible that they had the same relationship to some of the other feliform groups. (Werdelin and others)
Relationships among the first true cats are a little easier to follow because it’s possible to get molecular data from their living descendants.
This shows that the earliest true cats appeared at some point between 35 and 28.5 Ma. Then came the pseudaelurine cats, around 22 Ma, followed by the earliest “normal”-toothed cats and Sabertooth v4 – the sabercats – at roughly 14 Ma. (Werdelin and others)
That’s right – modern cats and sabertooths appeared at the same time. It’s not true, as many people think, that . . .
4. Modern cats are descended from sabertoothed cats.
All cats, living and extinct, look pretty much the same under the fur, except for size and the teeth. (Cope; Turner and Antón)
So in 1910 it was reasonable for paleontologists to explain the descent of cats this way (Matthew):
The early felids then, which were all comparatively large and very well armed for attack, were presumably specially adapted to prey upon the early large ungulates [hoofed plant-eaters…RH] and were all sabre-toothed . . . With the rise and dominance of the large light limbed ruminants [more hoofed plant-eaters…RH] and horses some of these early sabre-tooths were correlatively adapted into the modern type of felines . . .
In plain English, they felt that saberteeth turned into today’s “normal” feline teeth when prey evolved that were easier for the cat to catch.
Scientists accepted the idea that modern cats evolved from the sabertooths for much of the twentieth century, but hardly anyone believes it today.
In 2005, researchers (Barnett and others, 2005) analyzed some Smilodon DNA from the incredibly well-preserved sabertooth fossils at La Brea tar pits in California. The results proved beyond doubt that sabertooths were not the ancestors of any living cat.
Yes, scientists have sabercat DNA from both Smilodon and Homotherium.
Apparently some DNA can last for thousands of years, though not over really deep time (in other words, don’t hold your breath waiting for a real-life Jurassic Park).
And sabercats only went extinct about eleven thousand years ago.
So it may not be true that . . .
3. Sabercats are gone forever.
Late in 2012, the National Geographic Society held a closed meeting in its Washington, D.C., headquarters, where, they say
. . . a group of geneticists, wildlife biologists, conservationists and ethicists . . . gathered to discuss the possibility of de-extinction. Could it be done? Should it be done? One by one, they stood up to present remarkable advances in manipulative stem cells, in recovering ancient DNA, in reconstructing lost genomes. As the meeting unfolded, the scientists became increasingly excited. A consensus was emerging. De-extinction is now within reach.
China is already producing 500 clones of modern animals a year.
Experts at the same South Korean company that’s now cloning dogs hope to resurrect mammoths. (Zimmer)
The South Korean “cloning gurus” (note: there are closeups of dead, mummified week-old cats at this link) are also trying to bring cave lions back from extinction, using the remains of one of the two well-preserved cave lion cubs that were found recently in Siberia.
Oh, and business journalists speculate that Neandertals might be easier to bring back than the passenger pigeon because we already have reconstructed their genome.
Not to worry, some experts say “. . . there’s no reason that we can’t have the first generations of passenger pigeons by something like 2022 to 2025.”
Just five or eight years from now.
Having discovered this issue for the first time while working on this post, oh, how I long for some popcorn, beautiful CGI dinos on the screen, soothing background music by John Williams . . .
Instead, on the one hand I’ve got some Hammond-like criteria for de-extinction candidates:
- Is society receptive to its revival?
- Does it offer potential economic or other societal benefits?
- Can adequate animal welfare be ensured?
- Will its introduction benefit other species?
- Is it of unique significance to science?
- Does it play a significant ecological role?
On the other hand there is the writing of someone who has been bringing prehistoric wildlife, particularly sabertooths, to life in drawings and paintings for many years:
. . . whenever I see a living big cat in the wild I get a very strong reminder of how much more than just osteology is needed to make a living animal. One cannot overstate how final extinction is . . . we will never fully know what it is that we lost, because . . . there are subtleties in the interaction of a species with its environment that will be lost forever . . . It is easy to forget that each animal (including ourselves) has only one life to live, and from that point of view, de-extinction for me has something in common with some of the worse aspects of animal experimentation.
Read the whole thing.
This is one of those issues that demand a personal response as soon as you grasp the implications.
I’m still working through this. If we must clone extinct animals, the Pleistocene-Park approach seems the way to go.
However, I think that all the sabercat we really need to have around these days is this:
This video has almost twenty-seven million views, as of this writing!
The right sort of love must be part of the process.
There is a healthy and an unhealthy love of animals: and the nearest definition of the difference is that the unhealthy love of animals is serious . . .
The two extravagances which exist on the edge of our harassed and secretive society to-day are cruelty to animals and worship of animals. They both come from taking animals too seriously: the cruel man must hate the animal; the crank must worship the animal, and perhaps fear it. Neither knows how to love it.
— G. K. Chesterton
What all of us nonspecialists also tend to overlook is that extinction is about life as well as death.
It gave mammals a chance to take over the world after the dinosaurs (and some other groups) died off around 66 Ma.
Wait a minute – sabertooths, mammoths, etc., weren’t around back then. When did they go extinct?
They all had their own encounters with mass extinction, because it’s not true that . . .
2. The last big mass extinction happened at the K/T boundary.
The last big mass extinction actually ended around ten thousand years ago, at the close of the last ice age. In this event, most large land animals died off everywhere but Africa. (Prothero, 2006)
Sabercats vanished, as did some “normal”-toothed cats like prehistoric lions and the cheetah-like Miracinonyx. (Antón)
However, mammoths shrank down to about three feet high (seriously!) and hung out on islands for another six thousand years. (Prothero, 2006)
The last big mass extinction before that was between roughly 8 Ma and 2 Ma, when over 90% of western Eurasia’s carnivores disappeared. (Werdelin and Turner)
This was the end of the barbourofelids, but it was a huge opportunity for “normal”-toothed cats. (Werdelin and Turner)
No one has worked out the details yet, but these cone-tooths just exploded onto the scene during this event.
The precise dates vary from researcher to researcher, but according to one widely recognized study (Johnson and others, 2006; O’Brien and Johnson), almost all eight modern cat lineages appeared at this time:
- Big cats: 10.8 Ma
- Bay cat lineage: 9.4 Ma
- Caracal lineage: 8.5 Ma
- Ocelot lineage: 8 Ma
- Lynx lineage: 7.2 Ma
- Puma lineage: 6.7 Ma
- Leopard cat lineage: 6.2 Ma
- Felis lineage (domestic cat): 3.4 Ma
Seven million years is a long time on the human scale, but in geologic terms, this is extremely rapid evolution!
The sabercats were affected by the extinction event, but they survived. Earlier lines disappeared and first Homotheriini, then the Smilodontini, in the form of Megantereon, appeared.(Werdelin and Turner)
And, for those who prefer to classify sabertooths by their lower canines, this event is the dividing line between earlier knife-tooths and the true sabertoothed cats. (Christiansen)
Less is known about earlier mass extinctions, since the fossil record of cats isn’t all that great past 10 Ma. (Turner and Antón)
But two events during the first half of the Age of Mammals stand out. They’re very relevant to the evolution of cat-like animals and cats, too.
Not to mention the rest of us.
- Ice: The Eocene-Oligocene climate transition, around 34 Ma. Greenhouse Earth had recently begun cooling down. Now, the first major ice sheets of the mammal age formed in Antarctica. (Zachos and others) Water for all that ice came from the ocean. Sea levels dropped; water barriers to migration disappeared; and the first feliforms and other advanced Asian animals, totally unaware of the bigger picture, walked into Europe and ended the reign of creodonts there. They also wiped out more than half of the locals in an extinction event scientists call the Grande Coupure (“Great Break”). Feliforms moving into Europe set the stage for the development of the first cats there some twelve million years later. (Agustí and Antón; Prothero; Werdelin and others)
- Fire: The PETM, around 55 Ma. Well, it was a really strong heat wave, and according to some experts, underground magma set off this Paleocene-Eocene Thermal Maximum by melting frozen methane that was stored in the seabed. (Svensen and others) Another possible scenario is that tectonic movements temporarily turned the Gulf of Mexico into a large pool that mostly evaporated, exposing the seafloor and releasing its methane. (Cossey and others) Why do scientists focus on the methane? Because it’s an even more efficient greenhouse gas than CO2 and is available to release such a sudden multi-gigatonne blast of greenhouse gases. The planet’s mean temperature soared some 10 Fahrenheit degrees or more during the PETM. This was a bad extinction event in the sea. On land, nobody dropped dead from all the extra gas, but more advanced mammals, including those that would evolve into nimravids, barbourofelids, and cats, replaced the archaic critters that had developed during the first ten million years of the mammal age. (Agustí and Antón; Prothero)
With all these extinctions and climate changes, it’s a wonder that any of us mammals have made it this far!
So how does the end-Cretaceous extinction compare with those described above?
It reduced global family diversity less than 10% in the ocean and only 15% on land – in this respect, the K/T event is the least intense of any of the Big Five major mass extinctions. (McGhee)
But by taking out key groups from dinos down to marsupials – one of the dominant mammal groups in North America then – the K/T extinction destroyed every ecosystem on Earth.(McGhee and others)
This makes it the second-worst ecological mass extinction in the geological record. (McGhee and others)
That is the difference between “big” and “major” mass extinctions.
1. Fossils are boring.
If you’ve made it this far, you know this isn’t true. But perhaps you’re just browsing and started off the list with #1.
Cats aren’t boring. This is a no-brainer with the big cats, but it’s also true of small cats. Yet when you put them in the museum, or in the lab, people start getting glassy-eyed.
Science is the problem.
There is some rule that requires scientists to express themselves only in multi-syllable words, equations, and graphs.
Unfortunately, the rest of us don’t have the “movie,” based on research and many years of study, that all paleontologists play in their heads as they talk about life on Earth in the past. All we encounter is the long words and math; and that’s not very interesting to most of us.
The Shanghai Science and Technology Museum has a sabercat-style fix for that. You don’t need to understand the language to understand this video.
Fossils may be dry bones now, but the living being they supported and the events that put them into the ground can be very exciting.
Per the English part of this YouTube page, these sabercats are Amphimachairodus species, and that hellhoundish thing they fight at the end is Dinocruta – a hyena-like feliform.
A fossil all by itself also can be amazing, if you know what you’re looking at. This one, for instance:
It looks like someone in the back room didn’t finish the assembly job. But see the foam and the mirror – experts wanted you to see all of this strange-looking thing.
And no wonder. Each piece is from a different animal.
It happened when two nimravids were fighting in Oligocene North America. One’s sabertooth got stuck in the other’s shoulder blade.
One nimravid couldn’t walk and the other couldn’t eat. They both died in the clinch.
Millions of years later, in the 1930s, one of the monkey people – a scientist – found this remnant of that epic battle and wrote a poem about it. (You can download it from the University of Nebraska here.)
. . . I wondered why
such perfect fury had been swept away, while men
wide-roaming dark assassins of his kind
had sprung up in the wake
of such perfected instruments as these . . .
We are all atavists and yet sometimes we seem
Wrapped in wild innocence like sabertooths, as if we still might seek
A road unchosen yet, another dream.
— Loren Eiseley, in “Innocent Assassins”
You see, nothing is really boring; there are only people who aren’t fully awake yet.
Note: I’m going to start the final draft of the book now and will post updates as I can. I’ll probably rearrange this website before the book comes out late this fall, too.
Featured image: Lion in Calgary Zoo with ball. Akoroq, https://pixabay.com/en/lion-calgary-zoo-lion-with-ball-1502933/ public domain.
Chillin’ villains, dog and cat. Andy McElmore. https://www.flickr.com/photos/andy_emcee/6416366321 . CC BY-SA 2.0.
Carnassial teeth: Cbrookes92. https://commons.m.wikimedia.org/wiki/File:ABCD_Carnassial_teeth.jpg . CC BY-SA 3.0.
Hyena and lion. lubye13. https://commons.m.wikimedia.org/wiki/File:Panthera_leo_%26_Crocuta_crocuta.jpg . CC BY-SA 2.0.
- Yellow mongooses: John5199. https://commons.m.wikimedia.org/wiki/File:Yellow_Mongoose_(7006325750)_(2).jpg CC BY 2.0.
- Genet in Wroclaw Zoo. Guérin Nicolas. https://commons.m.wikimedia.org/wiki/File:Genetta_genetta_felina_(Wroclaw_zoo).JPG CC BY-SA 3.0.
- Spotted hyena close-up. Tambako the Jaguar. https://www.flickr.com/photos/tambako/8997861116 . CC BY-ND 2.0.
- Fossa. Chad Teer. https://commons.m.wikimedia.org/wiki/File:Cryptoprocta_ferox.jpg#mw-jump-to-license . CC BY 2.0.
- Roto the African palm civet. Audrey Sel. https://he.m.wikipedia.org/wiki/קובץ:Roto_the_African_Palm_Civet.jpg . CC BY-SA 2.0.
- Fluffy being held. Azamaszota. https://pixabay.com/en/cat-kitten-animal-pet-1466612/ . CCO, public domain.
Cheetah and meerkatts video. Dolph C. Volker. \
Smilodon in the overhead branches. James St. John. https://www.flickr.com/photos/jsjgeology/15256732717 . CC BY 2.0.
Smilodon and prehistoric lion. Joe Mabel. CC BY-SA 3.0.
Lion and sabertooth skulls. Ryan Somma. https://www.flickr.com/photos/ideonexus/4060351722 . CC BY-SA 2.0.
Clouded leopard video. BBC One. Ingenious animals – Episode 2. Online preview.
Homotherium, the scimitar cat. Ghedo. https://commons.m.wikimedia.org/wiki/File:Homotherium_crenatidens.JPG . Public domain.
Sabertooth and sloth. Dallas Krentzel. https://www.flickr.com/photos/31867959@N04/6802033980 . CC BY 2.0.
Cave lions painting, Chauvet Cave (replica). HTO. https://commons.m.wikimedia.org/wiki/File:Lions_painting,_Chauvet_Cave_(museum_replica).jpg . Public domain.
Sabertooth hunt, version 1. AP Editing.
Sabertooth hunt, version 2. BBC Worldwide.
La Brea human skull, “La Brea Woman.” Franco Fonseca. https://commons.m.wikimedia.org/wiki/File:La_Brea_woman.jpg . CC BY-SA 2.0.
Nimravid cub. John Benson. https://commons.m.wikimedia.org/wiki/File:Hoplophoneus_juvenile.jpg . CC BY 2.0.
Saber-creodont. Ghedoghedo. https://commons.m.wikimedia.org/wiki/File:Machaeroides_eothen.JPG . Public domain.
Nimravus. James St. John. https://www.flickr.com/photos/jsjgeology/32697590381 . CC BY 2.0.
Dinictis and Protoceras. Charles R. Knight. Public domain.
Barbourofelis fricki. Ghedoghedo. https://commons.m.wikimedia.org/wiki/File:Barbourofelis_fricki.JPG . Edited by RH a little. CC BY-SA 3.0.
Felis and Smilodon skull drawing. Cope (see source list below). Public domain.
DNA person. NeuPaddy. https://pixabay.com/en/man-dna-spiral-biology-merge-2125123/. CCO, public domain.
Smilodon on Wilshire Boulevard. La Brea Tar Pits and Museum.
Elephant and turtle imagery. Thommas68. https://pixabay.com/en/turtle-elephant-animal-wild-nature-2361131/. CCO, public domain.
Dwarf mammoth. James St. John. https://www.flickr.com/photos/jsjgeology/32552878211 . CC BY 2.0.
Cheetah at a dog race. BBH London, per Snopes.
Fire and ice. Skeeze. https://pixabay.com/en/sunrise-harding-ice-fields-snow-2062953/ . Edited by RH. CCO, public domain.
Crocodile and tiger. Vickey Chauhan. https://en.m.wikipedia.org/wiki/File:A_male_tiger_with_huge_crocodile_at_Rajbaugh,_Ranthambhore.jpg . CC BY-SA 4.0.
Smilodon skeleton drawing. Cope, Figure 12 (See source list below).
Amphimachairodus life and death video. Shanghai Science and Technology Museum. (in Chinese language).
Two nimravids, one fossil (“Innocent Assassins”): James St. John. https://www.flickr.com/photos/jsjgeology/31968700984/ . CC BY 2.0.
Star Thrower video: Vezari Studios
CITED AND UNCITED REFERENCES
Agustí, J., and Antón, M. 2002. Mammoths, sabertooths, and hominids: 65 million years of mammalian evolution in Europe. New York and Chichester: Columbia University Press.
Antón, M. 2013. Sabertooth. Bloomington: Indiana University Press.
Averianov, A.; Obraztsova, E.; Danilov, I.; Skutschas, P.; and Jin, J. 2016. First nimravid skull from Asia. Nature, Scientific Reports. doi:10.1038/srep25812.
Barnett, R.; Barnes, I.; Phillips, M. J.; Martin, L. D.; Harington, C. R.; Leonard, J. A.; and Cooper, A. 2005. Evolution of the extinct sabretooths and the American cheetahlike cat. Current Biology. 15(15):R589-R590.
Barnett, R.; Zepeda Mendoza, M.L.; Rodrigues Soares, A. E.; Ho, S. Y. W.; and others. 2016. Mitogenomics of the extinct cave lion, Panthera spelaea (Goldfuss, 1810), resolve its position within the Panthera cats. Open Quaternary, 2, page 4.
Barnosky, A. D. 2001. Distinguishing the effects of the Red Queen and Court Jester of Miocene mammal evolution in the northern Rocky Mountains. Journal of Vertebrate Paleontology. 21(1):172-185.
Barycka, E. 2007. Evolution and systematics of the feliform Carnivora. Mammalian Biology. 72(5):257-282.
Benton, M. J.; Donoghue, P. C. J.; Asher, R. J.; Friedman, M.; Near, T. J.; and Vinther, J. 2015. Constraints on the timescale of animal evolutionary history. Palaeontologia Electronica, 18.1.1FC 1-106. palaeo-electronica.org/content/fc-1.
Bryant, H. N. 1991. Phylogenetic relationships and systematics of the Nimravidae (Carnivora). Journal of Mammalogy. 72(1):56-78.
Centaur. Via machine translator. (Just checking to see if you’re looking.)
Christiansen, P. (2013), Phylogeny of the sabertoothed felids (Carnivora: Felidae: Machairodontinae). Cladistics. 29: 543–559.
Chesterton, G. K. 1921. “On Seriousness,” in The Uses of Diversity: A Book of Essays. New York: Dodd, Mead and Company.
Cope, E. D. 1880. On the Extinct Cats of America. American Naturalist. xiv (12):833-857.
Cossey, S.P.J., and others: 2016. Compelling evidence from eastern Mexico for a Late Paleocene/Early Eocene isolation, drawdown, and refill of the Gulf of Mexico. Interpretation 4.1:SC63-SC80.
Flynn, J. J., and Galiano, H. 1982. Phylogeny of early Tertiary Carnivora with a description of a new species of Protictis from the middle Eocene of northwestern Wyoming. American Museum Novitates. 2725:1-64.
Francis, J. E., Marenssi, S., Levy, R., Hambrey, M. and others. 2009. From greenhouse to icehouse – the Eocene/Oligocene in Antarctica, in Developments in Earth and Environmental Sciences, Vol. 8, eds. Florindo, F., and Siegert, M., 311–372. Elsevier.
Geraads, D., and Peigné, S. 2016. Re-appraisal of Felis pamiri Ozansoy, 1959 (Carnivora, Felidae) from the Upper Miocene of Turkey: the earliest pantherin cat? Journal of Mammal Evolution.
Goswami, A. 2010. Introduction to Carnivora, in Carnivoran Evolution: New Views on Phylogeny, Form and Function, ed. A. Goswami, A., and Friscia, A., 1-24. Cambridge: Cambridge University Press.
Gradstein, F. M.; Ogg, J. G.; and Hilgen, F. G. 2012. On the geologic time scale. Newsletters on Stratigraphy. 45(2):171-188.
Graham, Alan. 2011. The age and diversification of terrestrial New World ecosystems through Cretaceous and Cenozoic time. American Journal of Botany. 98(3):336-351.
Haq, B. U. 2014. Cretaceous eustasy revisited. Global and Planetary Change. 113:44-58.
Heske, E. J. Fall 2013 semester. Mammalogy 462, online class notes. Lab 19: Carnivora 1. http://www.life.illinois.edu/ib/462 . Last accessed December 11, 2015.
Holliday, J. A., and Steppan, S. J. 2004. Evolution of hypercarnivory: the effect of specialization on morphological and taxonomic diversity. Paleobiology. 30(1):108-128.
Hunt, Jr., R. M. 2001. Small Oligocene amphicyonids from North America (Paradaphoenus”, Mammalis, Carnivora). American Museum Novitates. 3331:1-20.
Johnson, W. E.; Eizirik, E.; Pecon-Slattery, J.; Murphy, W. J.; Antunes, A.; and Teeling, E. C. 2006. The Late Miocene Radiation of Modern Felidae: A Genetic Assessment. Science. 311:73-77.
Kitchener, A. C., Van Valkenburgh, B., and Yamaguchi, N. 2010. Felid form and function, in Biology and Conservation of Wild Felids, ed. D. W. Macdonald and A. J. Loveridge, 83-106. Oxford: Oxford University Press, Oxford.
Luo, S-J; Kim, J-H.; Johnson, W. E.; van der Welt, J.; Martenson, J.; and others. 2004. Phylogeography and genetic ancestry of tigers (Panthera tigris). PLoS Biology. 2(12):e442.
Lyle, M., Barron, J., Bralower, T. J., Huber, M., Olivarez Lyle, A., Ravelo, A. C., Rea, D. K., and Wilson, P. A. 2008. Pacific Ocean and Cenozoic evolution of climate. Reviews of Geophysics. 46. RG2002
Martin, L. D. 1980. Paper 287: Functional Morphology and the Evolution of Cats. Transactions of the Nebraska Academy of Sciences and Affiliated Societies. VIII:141-154.
Martin, L. D. 1989. Fossil History of the Terrestrial Carnivora, in Carnivore Behavior, Ecology, and Evolution, ed. Gittleman, J. L., 1:536-568. Ithaca, NY: Cornell University Press.
Matthew, W. D. 1910. The phylogeny of the Felidae. 56.9.74F. Bulletin of the American Museum of Natural History. XXVIII:289-316.
McGhee, Jr., G. R., Sheehan, P. M., Bottjer, D. J., and Droser, M. L. 2004. Ecological ranking of Phanerozoic biodiversity crises: ecological and taxonomic severities are decoupled. Palaeogeography, Palaeoclimatology, Palaeoecology. 211:289–297.
Nyakatura, K., and Bininda-Emonds, O.R.P. 2012. Updating the evolutionary history of Carnivora (Mammalia): a new species-level supertree complete with divergence time estimates. BMC Biology. 10:12.
O’Brien, S. J. and Johnson, W. E. 2007. The evolution of cats. Scientific American. 297 (1):68-75.
Peigné, S. 2003. Systematic review of European Nimravinae (Mammalia, Carnivora, Nimravidae) and the phylogenetic relationships of Palaeogene Nimravidae. Zoologica Scripta. 32(3):199-299.
Person, J. J. 2012. Saber Teeth. Geo News. 39(2):13-16. PDF link. https://www.dmr.nd.gov/ndgs/documents/newsletter/2012JULY/SaberTeeth.pdf Last accessed June 28, 2017.
Prothero, D. R. 2006. After the Dinosaurs: The Age of Mammals. Bloomington and Indianapolis: Indiana University Press.
Prothero, D. R., and Heaton, T. H. 1996. Faunal stability during the Early Oligocene climatic crash. Palaeogeography, Palaeoclimatology, Palaeoecology. 127:257-283.
Revell, Jamie. 2010. Carnivores, Carnivorans, and Carnassials. https://synapsida.blogspot.com/2010/12/carnivores-carnivorans-and-carnassials.html Last accessed June 27, 2017.
Rose, K. D. 2006. The Beginning of the Age of Mammals. Baltimore: The Johns Hopkins University Press.
Salesa, M. J., Antón, M., Morales, J., and Peigné, S. 2012. Systematics and phylogeny of the small felines (Carnivora, Felidae) from the Late Miocene of Europe: a new species of Felinae from the Vallesian of Batallones (MN 10, Madrid, Spain). Journal of Systematic Palaeontology. 10(1):87-102.
Simpson, G. G. 1953. The Major Features of Evolution. New York: Columbia University Press.
Svensen, H.; Sverre Planke, S.; Malthe-Sørenssen, A.; and others. 2004. Release of methane from a volcanic basin as a mechanism for initial Eocene global warming Nature. 429:542–545.
Switek, B. 2016. The Dakota badlands used to host sabertoothed pseudo-cat battles. Smithsonian Magazine. http://www.smithsonianmag.com/science-nature/dakota-badlands-used-host-wild-sabertoothed-pseudo-cat-battles-180957841/ Last accessed June 30, 2017.
Turner, A., and M. Antón. 1997. The Big Cats and Their Fossil Relatives: An Illustrated Guide to Their Evolution and Natural History. New York: Columbia University Press.
Turner, A., Antón, M., Salesa, M. J., and J. Morales, J. 2011. Changing ideas about the evolution and functional morphology of Machairodontine felids. Estudios Geológicos. 67(2): 255-276.
van den Hoek Ostende, L.; Morlo, M.; and Nagel, D. 2006. Fossils explained (52): Majestic killers: the sabre-toothed cats. Geology Today. 22(4):150-157.
University of California Museum of Paleontology. 2005. Carnivora: More on Morphology. http://www.ucmp.berkeley.edu/mammal/carnivora/carnivoramm.html Last accessed June 28, 2017.
Van Valkenburgh, B., and Hertel, F. 1993. Tough times at La Brea: Tooth breakage in large carnivores of the late Pleistocene.
Werdelin, L. 1989. Carnivoran Ecomorphology: A Phylogenetic Perspective, in Carnivore Behavior, Ecology, and Evolution, ed. Gittleman, J. L., 2:582-624. Ithaca, NY: Cornell University Press.
Werdelin, L.; Yamaguchi, N.; Johnson, W. E.; and OBrien, S. J.. 2010. Phylogeny and evolution of cats (Felidae), in Biology and Conservation of Wild Felids, ed. D. W. Macdonald and A. J. Loveridge, 59-82. Oxford: Oxford University Press.
Werdelin, L., and Dehghani, R. 2011. Carnivora, in Paleontology and Geology of Laetoli: Human Evolution in Context, Volume 2: Fossil Hominins and the Associated Fauna, Harrison, T., ed., 189-232. Springer, Dordrecht.
Werdelin, L., and Lewis, M. E. 2001. A revision of the genus Dinofelis (Mammalia, Felidae). Zoological Journal of the Linnean Society. 132:147-258.
Werdelin, L., and Turner, A. 1996. Turnover in the guild of larger carnivores in Eurasia across the Miocene-Pliocene boundary. Acta Zoologica Cracoviensia. 39(1):585-592.
Wesley-Hunt, G. D. 2005. The Morphological Diversification of Carnivores in North America. Paleobiology. 31(1):35-55 .
World Heritage Encyclopedia. (n.d.) Illinois: Urbana. Project Gutenberg. Retrieved July 5, 2017, from http://www.self.gutenberg.org/articles/eng/Caniform
Zachos, J., Pagani, M., Sloan, L., Thomas, E., and Billups, K. 2001. Trends, rhythms, and aberrations in global climate 65 Ma to present. Science. 292:686–693.
Zimmer, C. 2013. “Bringing Them Back to Life.” National Geographic.com . http://www.nationalgeographic.com/magazine/2013/04/species-revival-bringing-back-extinct-animals/ . Last accessed July 10, 2017.