Here is one of the posts (revised) from my early 2018 series here on sabercats — beautiful creatures that I’d like to write an eBook about in a year or two from now.
You might have heard of Smilodon (of La Brea Tar Pit fame), but what about Nimravides and the Metailurini?
That sounds like a rock band, but these were two impressive and very different long-fanged feline groups:
- 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)
Very little is known about either group.
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 (see source list)
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.
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’s group of cats is not the only one that has ever existed. There are at least two known subfamilies in Felidae:
- Felinae, sometimes called the “conical-toothed” cats. These are modern cats — the only ones left standing after Family Felidae first appeared in the early Miocene (or possibly late Oligocene)
- Machairodontinae: “Knife-tooths,” i.e., the sabercats. Contrary to what many people think, sabertooths were actually very successful, highly evolved, and had a good, 14-million-year run (Werdelin and others.) until the last species finally went extinct some 12,000 years ago at the end of the last ice age.
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 those of the Knife-tooths and ancestral conical-toothed cats.
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.
The origin of Nimravides is where things get a little iffy again.
Around 12-14 million years ago, in the middle Miocene, did this cat:
- 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 North American home boy” hypothesis offer some possible candidates – local pseudaelurine species, like P. intrepidus or P. marshi, that Nimravides resembles. (Werdelin and others)
This resemblance could mean that one of these Pseudaelurus species evolved into Nimravides.
But this doesn’t rule out the possibility that Nimravides was related to a Knife-tooth species of Machairodus that migrated into North America from Eurasia, across the Bering land bridge, around 7 Ma (million years ago). (Hunt, 2004)
Some paleontologists report there are enough resemblances between Nimravides and Machairodus fossils, including but not limited to the saberteeth, to show that the two cats may be related. (Antón and others)
It’s not impossible. What if Pseudaelurus quadridentatus, the probable ancestor of sabercats, 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)
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, despite their closeness to us in time, there aren’t very many fossils available. And interpretations of what fragmentary evidence there is often vary from researcher to researcher. (Antón)
Everybody does accept these two Metailurini 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)
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 — North America, for Metailurus; Africa, for Dinofelis.
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 for Machairodontinae. (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 conical-toothed cats interacted with the Knife-tooths in many ways, and vice versa. (Turner and others; Werdelin and others)
It’s even possible that some modern cat species may have been one of the culprits behind the sabertooth extinction at the end of the last ice age!
It’s not just about saberteeth
When you get right down to it, besides their basic “catitude”, Metailurus and Dinofelis had only one physical detail in common: unusually small lower fangs. (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.
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.
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 these days to learn more about the evolution of cats.
Featured image: Metailurus major, cranial detail. Izvora, via Wikimedia, CC BY-SA 3.0.
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This series on sabertooths was originally posted at my Robin Huntingdon blog about a year ago.