“The First Cat” – Chapter Four Draft Excerpt

Margaykat_Leopardus_wiedii

One of the biggest questions about cat evolution is why the earliest true cats were built very much like their most advanced representatives. That beautiful shape appears in the fossil record right from the start.

Cat-loving laypeople are okay with this mystery. We know that shape is part of a cat’s essence, and you can no more pin that down than you can a drop of water. Like mountain streams cutting through granite, cats go where they will, when they will, no matter how the rest of the world does things.

So, instead of wondering about the why of it, let’s instead look at what experts are learning about the first stages in the evolution of cats.

Feliforms and caniforms

The split between cats and dogs isn’t just a figment of human imagination.

Using dental differences and the shape of the inner ear (Wyss and Flynn), biologists and paleontologists really do classify almost all carnivorans, living and extinct, as feliforms or caniforms.

  • Feliforms

    • Some feliforms besides modern cats are civets, mongooses, meerkats, and hyenas. Yes, hyenas look and sound like freaky dogs, but key internal details show that they’re really feliforms. The connection is more obvious in fossil animals.
    • Other extinct feliforms include the Ice Age sabertooths, and perhaps also nimravines and barbourofelids although that is debatable.
    • The oldest known feliform fossils were found in France and Mongolia—opposite ends of the vast continent of Eurasia. (Hunt, 1998) Those animals may have resembled palm civets, the most primitive feliform known today. (Rose, Heske)
  • Caniforms

    • Dogs, bears, walruses, raccoons, weasels, skunks, and otters are just some of today’s caniforms. It’s a very diverse group.

    • Caniforms also have a rich fossil record. The ancient caniforms that gave early cats the most trouble were amphicyonids, also known as bear-dogs. Along with creodonts, some amphicyonids were apex predators wherever they roamed. (Hunt, 1989)

    • When studying caniforms, experts usually keep dogs separate from everything else. In the caniform family tree, dogs are cynoids—a sister group to the rest, which are classified as arctoids. (Hunt, 1989)

Feliforms and caniforms probably evolved in North America and then migrated to Europe and Asia. (Antón, 2008) For most of them, this was during the Eocene, a time in geologic history when South America and Africa were surrounded by water.

Feliform and caniform carnivorans would eventually invade those two “island continents,” too, after land bridges had formed. And many millions of years after that, humans would finally introduce, first, dogs and then cats to Australia.

No one knows exactly how far back the feliform/caniform thing goes. It probably developed less than twenty million years after the Age of Mammals began (Antón, 2008), if it wasn’t built in from the start.

Experts are still working out the carnivoran family tree. The only point that has been established so far is that dogs are descended from miacids. (Rose)

Vulpavus was a miacid:

800px-Vulpavus_ovatus

Miacids were weasel- to fox-sized arboreal mammals. They looked very primitive, but they did have carnassial teeth. This means they ate meat, although some might have lived on insects or fruit.

Together with other small predators—the viverravids— miacids probably hunted birds, lizards, multituberculates, and other vertebrates in forest canopies from western North America to Eurasia. (Eisenberg; Hunt, 1989; Rose; Werdelin)

Viverravids resembled miacids, and the two are sometimes grouped together as miacoids. (Rose) Very little is known about miacoids, and they are a hot research topic today.

For us, the big question is whether cats are descended from viverravids, since dogs evolved from miacids.

That would make a nice symmetrical story, but unfortunately there is no fossil evidence whatsoever that the evolution of cats happened that way.

It’s also not a good idea to generalize too much from what we know about the evolution of dogs. They are a special case.

Dogs probably emerged in North America with the rest of the carnivorans, but they didn’t migrate out of there until long after the others had moved on. (Antón, 2008; Van Valkenburgh, 1999) Nobody understands why dogs waited thirty million years to leave home.

Perhaps it had something to do with their earliest development. Maybe dogs evolved differently than the feliforms and arctoids did.

However, until more fossil evidence is uncovered, it’s probably safe to say that miacoids are the source group—somehow—for both feliforms and caniforms (Rose), and ultimately, for cats and dogs. Beyond that simple point, it’s anybody’s guess.

One reason why it is so challenging to study miacoids is that the planet changed while they were living and evolving on it.

The whole planet.

Basically, in the middle of the Eocene geological epoch, the global “thermostat” failed. Earth’s climate cooled, and its water cycle switched over to a pattern with much less rainfall. (Lyle and others) Eventually what we call a “normal” climate developed.

What seems normal to us today is actually a pretty recent terrestrial development, when you take the long view.

Experts aren’t sure exactly why that middle Eocene cooling happened or how exactly it affected the evolution of life on Earth.

Miacoids certainly were adapted to a greenhouse. For hundreds of millions of years, Earth had been tropical, with heavy rainfall and very high levels of carbon dioxide. Miacids and viverravids evolved in this warm wet world and they thrived in it throughout the first half of the Eocene.

Feliforms and caniforms, on the other hand, came along as Earth’s climate and water cycle were moving into an “icehouse” setting. These up-and-coming carnivorans had the right adaptions and could definitely handle a cooler, drier world.

They spread across the northern continents, and dogs settled down in North America, while climate change progressed during the second half of the Eocene. Miacoids in those same places either went extinct or moved to tropical places that were isolated from a rapidly modernizing world.

Eventually, the miacoids made their last stand in Europe. (Prothero, 2006) But it wasn’t the Europe that we know today.

Sea level was much higher in the Eocene, so Europe was an archipelago. This lushly forested island chain sat in a sparkling tropical sea—Tethys, a global east-west equatorial connection between the Indian Ocean, the Atlantic, and the Pacific. (Lyle and others)

The land bridges hadn’t formed yet. At this point in the Eocene, all of Africa (with Arabia) and most of South America were still surrounded by water. The tropical water just off their northern coasts came from Tethys and returned to Tethys via the Indian Ocean.

640px-Palau_2008030818_4709_(2347767520) (1)

In Europe, miacoids and many other archaic mammals enjoyed this humid, familiar environment. The Tethys Sea also isolated them from the more advanced mammals that were taking over the continent.

Life was good on those islands. For a little while, anyway. Let’s leave the miacids and viverravids there, comfortable and unaware that they are about to go away forever.

It’s time for us to briefly shift our focus.

Major climate change happened just before cats arrived, so we need establish some Earth backstory for the rest of the Age of Mammals, as cats evolved.

But not much backstory. If we don’t use a light touch, the natural human fascination with cats might easily pull us into something that’s too big to wrap our minds around.

Cats did evolve during a very eventful time in Earth’s history. We can’t completely ignore those events.

But.

There’s a trap waiting for us in the fact that cats are always so in sync with their surroundings. This beautiful facet of cats doesn’t merely involve movement or fur coloration; it has something of the soul, too. A cat may live in a house but it actually seems to be the physical expression of Nature.

And we can hold it . . . and pet it . . . and listen to it purr.

That’s the trap. Because we love cats this way, we feel that checking out their evolution means trying to understand every little detail of how the world has shaped them and how cats, in turn, have shaped the world.

And that never works out.

It’s true that cats interact with their environment; some of them, the keystone predators, even control important parts of it.

But that environment also depends on climate, which in turn is affected by subtle shifts in Earth’s orbital geometry and the cumulative effects of plate tectonics. The orbital rhythms that bring on climate change also swing around a standard point that keeps drifting along with developments in the planet’s topography and geography, its ocean gateways, and its atmospheric makeup. (Zachos and others)

Cats—and the rest of us—interact constantly with all of that. In plain English, we have all evolved in a complex perpetual-motion machine.

Butterfly, meet hurricane.

Let’s just hit a few cat-related Earth highlights (these are from Lyle and others, except as noted) before picking up the story of cat evolution again with feliforms and caniforms:

  • You might already know that plate tectonics moves land masses over Earth’s surface; it also opens and closes ocean basins. (United States Geological Survey) The most influential direct effect, in terms of cat evolution, has been the construction of land bridges between Africa and Eurasia and between North and South America. (Agustí and Antón; O’Brien and Johnson; Van Valkenburgh, 1999) Indirect effects on climate have been important, too, but they are too complex to get into here.

  • It’s normal for the planet to go through warmer and colder phases, whether the overall setting is “greenhouse” or “icehouse.” With cat evolution, we will sometimes mention that Earth is having a warm or cool spell when we talk about habitat. Why habitat? Because . . .

  • There is more rainfall during Earth’s warm periods—warm air holds more moisture. (Strahler) Lush forests can grow in humid climates, so warm spells are good news for tree-dwelling cats, but cool spells, not so much. Cool air holds less water; therefore, less rain falls. Dense forests turn into scattered woodlands or even steppes and grassy plains when the climate is cool, and cats must adapt to life on the ground.

  • The middle Eocene “thermostat” failure ultimately led, through many slow steps, to Antarctica’s ice cap. However…

  • There’s no geophysical rule that says planets must have matching polar icecaps. The North Pole did eventually freeze over, for reasons that aren’t well understood, but that happened some ten million years after Antarctica permanently iced up. (Hay and others; Zachos and others, Figure 2)

  • While Earth has been at the “icehouse” setting, sea level changes have been controlled by glaciers and ice sheets. More ice makes sea level drop; melting ice raises the sea level. The details are surprisingly complicated. (Fjeldskaar; Mörner)
  • Even though cats aren’t native to Antarctica or the Arctic, the changes there have affected their evolution indirectly through sea level changes. Lower sea levels expose land bridges, like the Bering Strait migration corridor between Asia and North America, so groups can mingle. Higher sea levels isolate cats by blocking migration routes. (O’Brien and Johnson)

In the late Eocene, Tethys protected Europe’s old-fashioned miacoids by extending an inland seaway northward across Central Eurasia to the Arctic Ocean. It was a formidable migration barrier (Hunt, 1998), to the feliforms, caniforms, and other more advanced animals that now were thriving in Asia.

When the planet’s “thermostat” broke and glaciers started to form in Antarctica (Francis and others; Lyle and others), sea level fell and the Arctic end of the Tethys-Arctic strait became dry land. A small migration corridor opened in north central Eurasia, but there was still enough remaining water to keep transcontinental migration to a minimum. (Akhmetiev and Beniamovski)

But then, as a new geological epoch—the Oligocene—began, ice sheets in Antarctica dramatically expanded. Over a relatively short time, global sea levels plummeted almost two hundred feet [fifty-five meters]. (Lyle and others)

The inland sea covering Central Eurasia drained away completely. Animals could now walk from one end of the vast continent to the other.

Water also receded from what had been the islands of Europe, and much of the rugged Tethys seabed became dry land. It was rugged because geological changes, as Africa continued to drift northwards and India and Asia went on colliding, crumpled the seafloor. (Agustí and Antón)

Exposure of the craggy ridges and ranges of its former bed broke Tethys in two. Its southern half—the Mediterranean—was still a tropical sea, open on the east to the Indian Ocean through a narrow gateway. To the west, a region of complex straits connected the Mediterranean with the Atlantic Ocean. (Govers; Rögi)

The northern half of old Tethys—Paratethys—had become an inland sea that covered present-day central and eastern Europe. With very little inflow available from the Mediterranean, Paratethys began to evaporate. (Rögi)

Meanwhile, Europe was now part of the continent. Miacids and viverravids could handle that. There was enough tropical seawater around to hold off the worst effects of climate change. More clearings were breaking through the trees, but most of Europe was still covered by lush evergreen forest. (Agustí and Antón)

However, there were newcomers. The miacoids weren’t isolated any more, and they were too primitive to compete with the more developed feliforms and caniforms from Asia. Those old-style carnivorans soon went extinct, along with up to half of the other archaic European mammals from the Eocene. (Agustí and Antón; Rose)

Paleontologists call this turnover in western Eurasia “the Great Break.” Globally, about ten percent of all life on Earth disappeared around this time. (Keller, Figure 1)

Feliforms and caniforms, of course, survived, although they certainly weren’t apex predators in their new home, any more than they had been in eastern Eurasia. Creodonts and the new Asian nimravines were at the top of the food chain in Europe. (Hunt, 1998)

The carnivoran newcomers were under no pressure, and they quickly began to diversify.

Arctoids first evolved bear-like small creatures, and by the late Oligocene, some of these had become true bears, although they were still small. Several other small caniform predators also developed in Europe as the Oligocene wound down, and amphicyonids claimed the large caniform predator niche. (Agustí and Antón)

Molecular evidence suggests that the first cats emerged around the end of the Eocene/beginning of the Oligocene (Werdelin and others), but there is no fossil evidence yet to back that up.

At that point, even feliforms faced challenges. Nimravines had a lock on all felid niches except perhaps the stalk-and-pounce slot, since they had saberteeth. (Agustí and Antón; Hunt, 1998; Werdelin; Wesley-Hunt)

Nevertheless, feliforms managed to come up with several small carnivores that resembled modern civets and genets. (Agustí and Antón) More of these feloids arrived from Asia as the Oligocene progressed.

Stenoplesictis appeared in the middle of the epoch, along with Stenogale and Paleogale. It soon became the most common feloid in Europe. Perhaps Stenoplesictis was so successful because it had better carnassials than many of Europe’s caniforms during that time. (Agustí and Antón; D. E. Russell and others)

Some experts think that Stenoplesictis founded the group of carnivorans that modern civets are descended from. Others think that founder was Palaeoprionodon, another very common western Eurasian feliform in the Oligocene. (Hunt, 1998; Rose)

Nimravines began to thin out late in the Oligocene. There was room for more feloids now, including Haplogale and an advanced animal that many scientists believe was the first true cat. They call it Proailurus, the Dawn Cat.

Proailurus

If time travel were possible, cat lovers would head for late Oligocene Europe where, camped along the shores of a lake in what is now southern France, they might catch a glimpse of the first true cat.

These time jumpers would surely appreciate the fact that Earth had warmed up again after starting out the Oligocene with a big chill. At that point global temperatures were still some 5 to 9° F (3 to 4° C) warmer than they are today. (Naish and others)

Still, the humid nights could be chilly if there was a breeze. And nighttime would be when these travelers had to sit still outdoors in blinds for hours at a stretch, while prehistoric wildlife scurried through overhanging trees and prowled along the limestone shore around them.

Today, that lake is long gone, but tourists do visit the area, which is now a park. (Réserve Naturelle Nationale) Scientists go there even more often, and not to look at the park’s beautiful scenery.

This part of France is famous today for its fossils, including those of predators that once used fissures and caves in the soft limestone as lairs. It’s also the only place in the world where experts have identified beyond question the fossils of Proailurus. (Werdelin and others)

Proailurus is the Dawn Cat’s genus name, in the same way that Felis is the genus of housecats and some other small cats. And just as housecats also have a species name—Felis catus, or Felis silvestris catus on very formal occasions—Proailurus has at least three named species so far (Werdelin and others):

  • Proailurus lemanensis
  • P. bourbonnensis
  • P. major

Our time travelers would be looking for Proailurus lemanensis, the oldest known species. (Hunt, 1998) However, there could be no guarantee of seeing any of these rare creatures.

The visitors from the future would certainly see many creodonts at the lake. Those wolf-like animals were still apex predators in Europe, as well as in North America, Africa, and Asia, but they weren’t as diverse as they had been before the Great Break. Now, the more modern carnivorans that had replaced miacids and viverravids had much more variety than the old creodonts. (Hunt, 1998)

And no wonder! Most carnivorans were small predators. At just one fossil level in southern France there were at least two types of ancestral rabbit, six kinds of insectivore, two bat species, and over twenty different rodents. (Russell and others)

But now sudden excitement is spreading among the time travelers. Something that appears to be a cat has stalked out into the moonlight and is lapping up water at the lake’s edge. Nearby hoofed plant-eaters are eyeing it warily, poised to run.

Then the guide points out that this “cat” has saberteeth. The travelers didn’t notice those at first, though they do show a little bit. These long canines aren’t as dramatic as the ones displayed Smilodon, the last of the Ice Age saber-toothed cats and the one best known by the public.

This beautiful ghost isn’t the Dawn Cat. There were no true saber-toothed cats back then. It must be a “false cat”—one of the last nimravines, perhaps Nimravus itself. (Russell and others)

Like creodonts, the nimravines were in a decline now, but they were still apex predators on every northern continent. (Hunt, 1989) After all, here in proto-France there was also plenty of prey for large predators.

So, although it isn’t Proailurus, the cat lovers are thrilled to see a living nimravine. They were amazed at how much this ancient carnivoran resembled modern cats.

But they have it backwards. Nimravines evolved before cats did. It’s more correct to say that the first cats looked like nimravines, except for the saberteeth.

Cats only developed saberteeth later, after the nimravines had disappeared and their apex niche had been taken over by saber-toothed barbourofelids. And unlike the nimravines, barbourofelids were probably distantly related to cats. (Werdelin and others)

This almost identical appearance of two unrelated groups—nimravines and cats—is called convergent evolution.

Anyway, the Dawn Cat did have normal upper canines. (Cope) It was also the biggest feliform of its time (Peigné), nimravines aside. Most feliforms during the Oligocene weighed less than nine pounds (4 kg); some Proailurus individuals probably tipped the scale at over forty pounds (20 kg). (Hunt, 1998)

Back at the lake, just as a white glow is spreading low across the dark eastern sky, overhead leaves rustle violently and the scream of a terrified animal rips through the still predawn air. The little voice is silenced in mid-shriek.

Proailurus lemanensis has made its presence known by pouncing upon a hapless squirrel. (Agustí and Antón; Russell and others)

The time travelers who weren’t dozing when it happened see a flash of patterned fur amid the thrashing tree branches above their blinds, but wildlife cameras catch details that have passed too quickly for a startled human eye to follow.

The predator doesn’t drop the pitifully limp little furry body in its mouth while fleeing from the sudden human uproar down below. It’s a medium-sized modern-appearing spotted cat with unusually short legs. Scientists in the group know that, besides leg length, it also differs from modern cats in a few minor dental and cranial differences. Proailurus is a little more flat-footed than today’s cats, but nobody notices this on the film because of its incredible agility up in the trees. It moves much like today’s tree-dwelling fossas. (Agustí and Antón; Rothwell; Werdelin and others)

Where did such a beautiful animal come from? Paleontologists are still trying to work out the details of just how and where Proailurus evolved.

It wasn’t descended from the nimravines; that much definitely has been established. (Werdelin and others)

One idea is that Proailurus and two other feliforms present in that ancient French lake region—the cat-like Stenogale and the civet-like Haplogale—somehow all descended from a common ancestor that lived about five million years before them. However, the details of exactly how this led to Proailurus haven’t been worked out yet. (Hunt, 1998; Werdelin and others)

Another idea is based on a clue found in the New World. At a quarry in Nebraska, researchers found a few fossils of a cat which was more primitive than Proailurus, even though it lived after the Dawn Cat. This is peculiar, because primitive fossils of an animal are always older than more advanced fossils anywhere in the world.

Some experts suspect that the Nebraska discovery might mean that Proailurus wasn’t the only early cat. It could also mean that Proailurus or a similar, yet to be identified cat migrated into North America from Asia at a time when sea level was low enough to expose the Bering land bridge. (Hunt, 1998; Werdelin and others)

None of that has been proven yet, although some paleontologists say that Proailurus fossils have been found in Mongolia. (Hunt, 1998) However, others believe that those Asian fossils came from a barbourofelid. (Werdelin and others)

Cat fossils look so much alike that they sometimes puzzle even experts.

It would certainly be nice to find Proailurus fossils in Asia, and not just because the Dawn Cat might have evolved there with other advanced feliforms and then migrated into Europe and North America.

A proven Asian connection for Proailurus would also support the claim of some molecular biologists that a descendant of Proailurus known as Pseudaelurus lived in Asia and was the ancestor of all modern cats. (O’Brien and Johnson)

For now, this claim is based solely on lab work. Field evidence is scarce because there just aren’t very many known fossil locations from the right geological period in Asia. (Werdelin and others)

Using fossils from other areas, several paleontologists argue instead that Pseudaelurus founded the line of saber-toothed cats. In their version of the cat family tree, the ancestor of modern cats was another Proailurus descendant called Styriofelis. (Salesa and others, 2011 and 2012; Werdelin and others)

Who is right? No one knows, because the history of cat evolution has many gaps.

Each expert above holds just a small piece of the puzzle. These pieces sometimes seem to clash because they belong in different parts of the big picture, not side by side.

What that final picture might look like depends on how you see the cats that followed Proailurus in the fossil record. Those include Pseudaelurus, the sabertooths, and the first modern cats.

Pseudaelurus and the saber-toothed cats are extinct. They haven’t left us any DNA, so we can only talk about their fossils.

This makes things simpler, but you should know that Pseudaelurus can be tricky as well as fascinating.

The Pseudaelurus complex

It’s not exactly wrong to say that the cat family tree goes from Proailurus to Pseudaelurus and then on to the rest of the living and extinct cats. It’s just not the full and fascinating story, as far as scientists have pieced that together so far.

After it appeared in the late Oligocene, the Dawn Cat thrived in Europe for several million years, on into the next geological epoch, which is called the Miocene. Then it went extinct, as even the most successful species eventually do.

About a million years after the last known fossils of Proailurus (Werdelin and others), another type of cat fossil appeared.

This early Miocene animal was only as big as a housecat. The subtle details that paleontologists study were more modern in this cat than they had been in Proailurus.

The new cat lived in what is now Germany. Its bones were mixed in with those of other, more primitive cats that could be related to Proailurus. Scientists named the more streamlined kitty Pseudaelurus turnauensis. (Salesa and others, 2011)

It’s the oldest known Pseudaelurus fossil (Werdelin and others), but P. turnauensis is far from being the only specimen Almost all cat fossils from the early and middle Miocene are Pseudaelurus. And that’s a problem.

Cats didn’t really start getting diverse until the late Miocene, when the sabertooths came along. (Rothwell) Before that, most cat fossils were identical except for size. Since there was no good way to tell them apart, twentieth-century paleontologists filed everything from the right time period as “Pseudaelurus.” (Salesa and others, 2011)

Now that more fossils and better research tools are available, experts are reviewing Pseudaelurus fossils. This challenging work is ongoing, but they have already learned that at least some of those ancient felids probably came from different groups.

In other words, “Pseudaelurus” is really a collection of subgroups, not a single genus like Proailurus or Felis. (Werdelin and others)

Right now, three genus names for members of the Pseudaelurus complex are used frequently:

  • Pseudaelurus: Yes, this is confusing. Here’s how to tell the genus and the complex names apart: Look for italics on the genus. That is, we might talk about the fossils of Pseudaelurus turnauensis or the likelihood that saber-toothed cats all descended from Pseudaelurus quadridentatus, a member of the Pseudaelurus complex.
  • Hyperailurictis: All North American members of the Pseudaelurus complex. (Werdelin and others) We can call them Pseudaelurus—the genus name “Hyperailurictis” is part of a scientific debate that hasn’t been settled yet.
  • Styriofelis: We’ll look at this one more closely in the section on the ancestor of modern cats.

Now back to the Miocene.

After Germany’s P. turnauensis, at least three additional Pseudaelurus species soon showed up in Europe’s fossil record. This speedy evolution convinces some experts that all four Pseudaelurus species probably evolved from a single Proailurus species. (Salesa and others, 2012; Werdelin and others)

Of those four, only little Pseudaelurus turnauensis and leopard-sized P. quadridentatus hung on into the late Miocene. They were still around when the first known true saber-toothed cat, Miomachairodus pseudailuroides, appeared in Turkey. (Salesa and others, 2011; Werdelin and others)

In North America, the earliest cat—Pseudaelurus validus—is a very famous member of the Pseudaelurus complex. This cougar-sized middle Miocene animal ended the North American “cat gap.”

That gap had begun in the late Oligocene, when nimravines went extinct in North America late in the Oligocene (Van Valkenburgh, 2007), although they would still prowl around Europe and southern Asia for a few million years more. (Agustí; Hunt, 1989)

There were no cats in North America to take their place. Dogs and other caniforms evolved new hypercarnivorous species to fill the niche (Van Valkenburgh, 2007), but no felids appeared there for six million years.

Then Pseudaelurus validus showed up in Nebraska and New Mexico. (Rothwell) At least four more species followed, with the smallest being the size of a modern housecat. (Werdelin and others)

And, whether you call them Pseudaelurus or Hyperailurictis, none of them survived past the middle Miocene.

This group may have had such a short span of existence because life was hard on arboreal cats in Miocene North America.

Climate change was hitting the continent hard. Forests there had been shrinking since the Oligocene, and now savanna lands were opening up. (Martin, 1989) Central North America’s extensive grasslands, dotted with small live oaks and pines, as well as shrubs, berry bushes, and sagebrush (Webb), were very different from the subtropical oak-laurel forests of western Europe that Proailurus and Pseudaelurus called home during the early Miocene. (Agustí and Antón)

And every year now, probably because the northern Pacific Ocean was cooling (Lyle and others), less and less rain was falling on western North America during the summer, although winters there continued to be wet. Soon there would be little to no summer rain at all, and deserts would form in the western interior.

In addition, North America, unlike Europe or Asia at this point, was dog country. True dogs had first appeared there in the Eocene. Now there were at least twenty different canid species running around. (Antón, 2008) That’s in addition to all the other very successful Miocene caniforms: amphicyonids, true bears, and the ancestors of weasels, skunks, and otters. (Werdelin)

This type of climate change was ideal for pursuit hunters and long-legged large plant-eaters because it opened up North America’s forests, but tree-dwellers had an obvious problem.

There was plenty of prey available for small to medium-sized cats, but it was all on the ground, where those well-established caniforms ruled.

Nevertheless, tree-dwelling Pseudaelurus validus popped up in western North America, from who knows where, six million years after the last nimravine had called it quits.

It seems crazy, but there might have been a method to this cat’s madness.

Most Pseudaelurus fossils come from a region that had been reshaped by the growth of the Rocky Mountains and an associated episode of intense volcanism that had ended just before the cat arrived.

How intense was that volcanism? Let’s just say that over twenty of Earth’s forty-seven largest known explosive eruptions had happened there during the last thirty million years before Pseudaelurus showed up. (Mason and others)

They were all supereruptions, too: VEI 8 or larger. One of them—La Garita, occurring about halfway through the Oligocene—may have been at the upper limit of what the planet is capable of erupting. (Mason and others)

Geologists call that incredibly violent episode in Earth’s history the ignimbrite flare-up, since ignimbrite is a volcanic deposit left by pyroclastic flows.

What does it all have to do with cats? A layperson can speculate that it might have gotten them away from North America’s dogs.

The landscape built by the unusual geological situation that triggered the flare-up and caused other changes was probably very rugged in the middle Miocene, just as it is in Yellowstone Park and the rest of western North America today.

And just like today, there were probably forests at higher elevations, even in a dry climate. There were certainly no extensive low-lying plains to attract packs of pursuit hunters. A cat could survive here without encountering too many caniforms.

Whether or not that’s what happened, Pseudaelurus definitely was there in the middle Miocene, hunting rodents and other small prey in what are now the US states of Nebraska, Texas, New Mexico, Colorado, Nevada, and California. (Rothwell)

And then it vanished . . .

 

LIST OF IMAGES

Margay, by Malene Thyssen, Dual license: GNU Free Documentation License, Creative Commons Attribution ShareAlike 2.5.

Vulpavus, by GhedoghedoCreative Commons Attribution-Share Alike 3.0 Unported license.

Palau, by LuxTonnerreCreative Commons Attribution 2.0 Generic license.

Sources (sample)

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Post last edited March 15, 2016.

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