The Sabertooths, Part 6: The “Other Sabertooths”

Nimravides and the Metailurini.

It sounds like a rock band, but these were once two real and very different types of long-fanged big cat:

  • Nimravides. Long-legged and at least the size of a modern lion (Antón; Hunt, 2004), this mysterious sabercat prowled North America during the late Miocene, some 10-12 million years ago.
  • The Metailurini. Part sabertooth, part “normal” cat, Metailurus and its possible tribe had a much wider range than Nimravides. Some of them were the most common Pliocene felids in Africa. (Werdelin and Dehghani)
632px-metailurus_metailurus_major_asenovgrad2

Metailurus fossils aren’t as impressive as Smilodon’s, but this cougar-like Miocene cat was tough enough to thrive alongside the big sabercats.

Very little is known about either one of them.

Of course, geoscientists don’t know much about many of the other things found while digging around in the earth, either.

On this blog, we don’t need to go into “iffiness” very often to get to Wonder. Still, it’s good to be aware that, as a noted geoscientist puts it:

“I am fond of saying that a geologist writes like a person overcoming very grave reservations. This is because no geologist can operate as an earth historian without continuously doubting such opinions—regardless of the accuracy of the observations upon which they are based. The realization of our uncertainty makes us uneasy, as does knowing that our explanations of the past are not more true, but only more plausible, than the stories told by creationists, extraterrestrialists, and other seers.” (Van Couvering)

Paleontologists still have many “grave reservations” when discussing Nimravides and the Metailurini.

Yet the basic facts are clear enough.

Both cat groups developed around the same time as the early members of the Homotheriini and Smilodontini. Then they coexisted somehow with those impressive sabercats for a reasonably long time.

Nimravides didn’t make it out of the Miocene epoch (Werdelin and others), as far as anyone knows at this point.

The last member of the Metailurini died relatively recently, during the second half of the Pleistocene. (Werdelin and Dehghani)

All of these “other” sabertooths were very successful predators, and here is their story, as far as I understand what researchers have been able to outline to date.

Nimravides

Probably the least controversial way for a layperson to introduce this sabertoothed cat is to say that it first appeared in North America 12 to 14 million years ago. (Werdelin and others)

We’re on sure ground saying it “appeared” because Nimravides definitely shows up in the fossil record. (After all, “present” is almost the only fact that anyone really knows about any cat.)

More specifically, experts report that:
“…at ~16.5-17 Ma [million years ago], the first felids enter[ed] North America from Eurasia and persist[ed] as relatively small, lynx- to leopard-sized cats until the appearance of the large lion-sized felid Nimravides…” (Hunt, 2004)

A felid is any member of the cat family, Felidae. But there’s a little more to it than that, considering how many cats have roamed this planet down through geologic time.

  • Today we live alongside the only surviving felid subgroup – Felinae, sometimes called the “conical-toothed” cats.
  • The other major subgroup – Knife-Tooths, i.e., sabercats or Machairodontinae – is extinct.

Some experts think that Nimravides may have represented yet a third subgroup. (Werdelin and others) If so, its fossils have only been found in North America, unlike the other two subgroups.

With this early Miocene immigration of Eurasian felids into North America around 17 Ma, there were now cats on every major land mass except Australia and South America.

Even before then, North America might even had some native felids, though this is only speculation. There is no solid evidence yet that this was the case. (Werdelin and others)

Anyway, as far as anyone knows now, every cat was a pseudaelurine cat – descended from Proailurus, the Dawn Cat, with “dawn” happening roughly 27 Ma. (Werdelin and others)

There must have been different species, though, because pseudaelurines evolved into at least two cat groups (three, if you count Nimravides). Paleontologists are hard at work, identifying and improving their knowledge about these founder kitties.

In life, Nimravides was indeed as big as a modern lion. It had a heftier build, though – like a tiger, with very long, muscular legs. (Antón, Figure 3.39; Hunt, 2004; Martin, 1980; Turner and Antón)

Nimravides also had saberteeth like those of Machairodus – the Old World sabertoothed cat that we met earlier in this series.

And this is where things get a little iffy again.

In the middle Miocene, around 12-14 Ma, did Nimravides:

  • Emerge first in Eurasia as Machairodus and then travel across the Bering land bridge into North America? (Antón)
  • Evolve locally from those early lynx- and leopard-sized felid immigrants to North America mentioned above by Hunt? (Werdelin and others)

No one knows for sure. (Werdelin and others)

The history of pseudaelurine cats is fairly well understood in Europe, and to a lesser degree in Asia (where there aren’t that many helpful outcrops from the right geological epoch, according to Werdelin and others), but paleontologists have yet to find Nimravides’ fossilized ancestor in North America, if it exists.

Supporters of the “Nimravides was a home boy” hypothesis offer some possible candidates – local pseudaelurine species, like P. intrepidus or P. marshi, that Nimravides resembles. (Werdelin and others)

The resemblance could mean that one of these cats evolved into Nimravides.

After all, both Intrepidus and Marshi were big, like the probable sabertooth ancestor P-Quad, a/k/a Pseudaelurus quadridentatus. (Antón)

They were also very common, accounting for three-quarters of the North American Pseudaelurus fossils that have been found thus far. (Rothwell)

But this doesn’t show whether Nimravides was related to a Machairodus species that showed up in North America around 7 Ma. (Hunt, 2004)

According to the “home boy” view, Machairodus arrived from Eurasia, and Megantereon soon followed. (Hunt, 2004)

Then, from this point until around 4.5 Ma – when Nimravides finally went extinct without leaving any descendants (Werdelin and others) – sabertooths, smaller “normal” cats like the lynx, and Nimravides coexisted in North America. (Hunt, 2004)

But some paleontologists find too many resemblances between Nimravides and Machairodus, including but not limited to the saberteeth, for it all to be a coincidence. (Antón and others)

What if P-Quad originated in Asia, back in the late Miocene, not in Europe where all of its fossils have been found so far? (Antón)

Then some individuals could have headed west into Europe and evolved into Machairodus. Others – the ancestors of Nimravides – might have traveled eastward over the Bering land bridge into North America. (Antón)

This alternative version works so well with one Nimravides species that experts have changed its name from Nimravides catocopis to Machairodus catocopis. (Antón and others; Fossilworks)

But for the other four recognized Nimravides species (Werdelin and others) . . . not so much.

Perhaps those species did descend from the early North American pseudaelurines. (Antón and others)

The scientific controversies over Nimravides will probably continue until paleontologists can establish just how the Pseudaelurus complex of cats got started, and what relationships there were among pseudaelurines in Europe, Asia, and North America. (Antón; Werdelin and others)

The Metailurini

This group of prehistoric cats roamed Africa and the nothern continents for some nine million years. (Antón)

Paleontologists have lots of “grave reservations” about them, even though the Metailurini lived much closer to our own time than Nimravides did.

First, there aren’t very many fossils available. Different experts often interpret what fragmentary evidence there is differently. (Antón)

Everybody does accept these two groups:

  • Metailurus. Ranging in size from a modern snow leopard to a large cougar, this Miocene cat apparently evolved in Eurasia. (Werdelin and others) It had moderately long, flat upper canines and was slightly more advanced than P-Quad, which it resembled. (Antón)
  • Dinofelis. This cat probably first showed up in Africa (Werdelin and Lewis) and then traveled to Eurasia and North America. (Turner and Antón) It was generally bigger than Metailurus, up to small-lion in size. (Antón) More muscular than a modern leopard, Dinofelis had the same overall proportions. Some species had moderately flat but not very long saberteeth; others had almost “normal” teeth, like today’s conical-toothed big cats. (Werdelin and Lewis)
mountain-lion-1055259_640

Metailurus is often compared to a cougar.  Experts say you can’t get an accurate reconstruction by simply adding saberteeth to a modern animal, but it’s tempting.

Just for the record, other groups associated with the Metailurini are Adelphailurus, Stenailurus, Pontosmilus, and Fortunictis. (Antón; Berta and Galiano; Werdelin and others)

However, things quickly get very technical when you start looking into those names, so let’s just move on to Metailurini controversies that are easier for laypeople like us to understand.

For example, where did these cats come from? The pseudaelurine cats apparently had disappeared before the Metailurini arrived.

Even if we just look at Metailurus and Dinofelis, nobody knows how they evolved or whether they were even closely related to each other. (Werdelin and others)

Their evolution was centered on different continents.

Too, Dinofelis was most successful during the Pliocene and Pleistocene epochs. Metailurus had its heyday in the Miocene, millions of years earlier. (Werdelin and others)

Some paleontologists suspect Metailurus may have given rise to Dinofelis. (Beaumont, quoted by Werdelin and Lewis)

Others just group these two together because they were clearly different from modern cats but didn’t have enough sabertooth features to qualify as sabercats. (Werdelin and others)

Were Metailurus and Dinofelis “Knife-Tooths” with only slight to moderate saberteeth, or were they “normal” cats (Conical-Tooths) with a tendency toward a few sabertooth characteristics? (Antón; Werdelin and others)

No one can say for sure yet.

Only one thing is clear – when it came to saberteeth, Dinofelis just couldn’t make up its mind.

The oldest and youngest Dinofelis species were definitely sabertooths (Werdelin and others), but some species in between had upper canines that weren’t much different from those you’ll see in today’s lion. (Werdelin and Lewis)

In fact, one species –Dinofelis cristata – may be the only known case where a sabertoothed cat switched over to “normal” upper canine function! (Werdelin and Lewis)

This flexibility – going from sabertooth to “normal” back to sabertooth again – leads some paleontologists to suspect that Knife-Tooths and “normal” cats competed much more directly than previously thought. (Turner and others)

We don’t know exactly how they hunted, but the sabertooths probably went after big prey (Antón; Turner and others), leaving smaller prey to the “normal” cats that were also evolving back then. (Werdelin 1989)

Theoretically, the two groups of cats could have easily shared resources because their hunting techniques were different.

But the variability in Dinofelis teeth may show that cats had more hunting options than just “sabertooth” and “normal.” (Turner and others)

This in turn could mean that “normal” cats interacted with the sabertooths in many ways, and vice versa. (Turner and others; Werdelin and others)

It’s even possible, as we will see tomorrow, that some modern cats may have been one of the culprits behind the sabertooth extinction at the end of the last ice age.

Only time and more research can tell how much each group of cats – Knife-Tooths and Cone-Tooths – affected the other group’s evolution.

Another way to look at sabertoothed cats

When you get right down to it, besides being cats, Metailurus and Dinofelis had only one physical detail in common: their lower canine teeth were unusually small. (Turner and others)

And this obscure dental detail, according to some researchers, may eventually prove beyond question that the Metailurini were Knife-Tooths.

Most of us go by the sabers when defining a sabertoothed cat.

However, as we saw last time, there is also a “sabertooth complex” of physical features that include a more powerful body and, of crucial importance to us here, a arch of very large incisors. (Antón)

Paleontologists know that, as the upper canines turn into saberteeth and the incisors get bigger, lower canine fangs usually get smaller to match the incisors.

wp-1485383666152.jpeg

This reconstruction of “Barbourofelis loveorum” suggests how arcs of seriously-bite-sized incisors/lower fangs could be useful to a sabertooth.

A researcher now says that the size of lower canine teeth may be more important than sabers when it comes to sorting out sabertoothed cats.

He ran an advanced computer analysis on selected sabertooth fossil features to see what patterns showed up among the different sabertoothed cats. (Christiansen)

Surprisingly, the conventional groups of Homotheriini, Smilodontini, and Metailurini didn’t show up. (Christiansen)

Instead, Metailurus and Dinofelis, as well as Nimravides – and even Machairodus and Promegantereon! – were all linked together, mostly because their lower canines were all reduced in size. (Christiansen)

Dr. Christiansen calls these cats the Machairodontinae (Knife-Tooths). He uses the name Eumachairodontinae (True Knife-tooths) for the later saber-cats, including Megantereon, Smilodon, Amphimachairodus, Homotherium, and Xenosmilus, who sported “true” saberteeth.

amphimachairodus

Amphimachairodus giganteus.

This view is not widely accepted yet, and there are some criticisms. (See Spassov and Geraads, “Cladistic Analysis”)

We’ll have to see how this idea turns out over time.

But it’s a good example of how paleontologists are using some very advanced tools to learn more about the evolution of cats.

fossil-studier-478x346

“Here, kitty, kitty . . . “


Images:
Featured image: Metailurus major, cranial detail. Izvora. Asenovgrad Paleontological Museum. CC BY-SA 3.0.

Metailurus major. Izvora. Asenovgrad Paleontological Museum. CC BY-SA 3.0.

Puma. Skeeze. http://pixabay.com/en/mountain-lion-puma-cougar-wildlife-1055259.  Public domain.
Barbourofelis loveorum, Florida Museum of National History Fossil Hall at University of Florida: Dallas Krentzel. CC Y 2.0.

Amphimachairodus. Ghedoghedo. See page for licensing.

Fossil studier. John Day Fossil Beds National Monument staff (National Park Service). Public domain.


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This series on sabertooths was originally posted at my Robin Huntingdon blog about a year ago.


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