The Sabertooths, Part 7: Extinction

Why did sabertoothed cats go extinct? Easy. More sabercats died than were born.

How did it happen? Ah, well – that’s not quite so straightforward.

It doesn’t take much to wipe out any living group: a loss of just 1% of the population per year means extinction in a century. (Oppenheimer)

And that one-percent annual loss is so very possible in any group, given all the factors involved.

In order to exist, all cats must do the following, 24/7/365:

  • Use whatever resources are around, sharing or competing for them with other cats.
  • Keep up with the changes in prey animals that can evolve rapidly and in a variety of ways.
  • Have sex and raise kittens.
  • Adapt as a population to climate changes and the resulting effects on the ecosystem.
  • Stay healthy as individuals and avoid becoming prey themselves.

This list makes our own morning commute and the typical pressures of daily modern life a little easier to face!

Sabertoothed cats did all those things for at least 12 to 14 million years. Somewhere in there are the keys to their early development, their greatest successes, and their eventual extinction.

Unfortunately, most of those details don’t fossilize; also, “prehistoric” means events that happened before written records became a thing. Paleontologists must use indirect evidence to reconstruct the world the sabercats lived in, dominated, and ultimately lost to.

Such evidence is often vague enough to allow several interpretations. That’s why there are different schools of thought on almost anything from Earth’s past.

The fact that paleontologists only have a few of the many cat fossils that are probably out there (Johnson and others) doesn’t make this research any easier.

Another reason why it isn’t easy to say what killed off the sabercats is that scientists can’t be sure, even for modern animals, which has a bigger influence on evolution – the physical environment or interactions with other living beings. (See details in Barnosky; Ezard and others)

It could have been environment, negative contacts with other life around them, or a combination of the two.

At this point, no one really knows what tipped the scales against the last sabertooths – Smilodon, Homotherium, and Xenosmilus. (Werdelin and others, Figure 2.2)

One surprising clue is the fact that today everybody has to go to Africa in order to see most of the world’s really big land mammals.

Of course they do.

But paleontologists report that, up until the end of the last Ice Age – and for at least the last 50 million years before that – big mammals were common on every known continent (Antarctica’s history is concealed by its 33-million-year-old ice cap). (Prothero, 2006; Stuart)

This was true right up until the last days of the sabertoothed cats. Now, since the great ice fronts retreated poleward, you must journey to Africa to see big game in the wild.

The disappearance of sabercats was just part of a wider event called the end-Pleistocene megafauna extinction.

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Sure, you’ve probably heard about the Ice-Age mammoths and mastodons. In North America there were other colossal animals, including beavers as large as a modern bear as well as buffalo with a 6-foot (2-meter) horn spread. (Prothero, 2006)

And there was Arctodus, a 1,500-pound (680-kilogram) bear – the largest carnivoran that has ever lived. (Prothero, 2006)

In Europe, sabertooths could hunt gigantic hippos, rhinos, and the “Irish elk” – a moose-like creature that was neither Irish nor elk – as well as other enormous prey. (Antón; Prothero, 2006)

It was the same old 50-million-year-old story, this time with a Pleistocene cast of characters.

Then, over 10 thousand years ago, the last continental ice sheet melted away and the world warmed back up into its present climate.

That was nothing unusual – this glacial-interglacial swing has been going on for some three million years. But this time, when the excess ice went away so did most of the megabeasts. (Prothero, 2006)

North and South America, as well as Australia, were the hardest hit, although extinctions were also common in northern Eurasia. (Stuart)

Yet at least half of all the other mammal groups from those days – mostly small- to medium-sized animals – are still around. (Prothero, 2006)

Sabertooths and their prey could have easily handled the ice ages by migrating toward the Equator every 120,000 years or so as great glaciers advanced. Then they would follow their usual habitat back toward the pole as ice gradually melted and the next interglacial warm period began. (Prothero, 2004)

Something must have been different at the last glacial-interglacial transition.

It does appear as though life was a struggle for big carnivores then. Tooth fracture studies at La Brea show that all of the prehistoric carnivores there broke their teeth more often than modern ones do, probably while picking bones clean. (Van Valkenburgh and Hertel)

Researchers are still working on what that might mean in the bigger picture.

In case you’re wondering, there is no clear-cut evidence that the extinction of the big Ice-Age meat-eaters happened because their prey died out. (Stuart)

The sabertooths did vanish at different times on different continents. For example, per Werdelin and others:

  • Africa: This was no refuge for sabercats. Homotherium disappeared there about 1.4 Ma.
  • Europe: Homotherium vanished 500,000 years ago.
  • North America: Homotherium went extinct some 10,000 years ago (Antón), and some of the last Smilodons sank into La Brea’s fatal embrace around 13,000 years ago.

Some experts on ancient life suggest that these extinctions coincided with the arrival of humans on each continent. (Antón)

Others, while noting that manmade extinction has indeed happened on islands, say that the intercontinental Pleistocene extinctions can’t be explained so easily. (Prothero, 2006)

New findings can change things dramatically, but right now it looks like the sabertooths and their prey were probably affected by a complex series of events related both to the arrival of modern humans and to environmental changes. (See Stuart, as well as discussion in Prothero, 2006, Chapter 8, “Death of the Megamammals”)

Those environmental changes must have been complex, and it’s possible that another, perhaps very competitive predator besides Homo sapiens may have been in the ecosystem along with the sabertoothed cats.

We know that gigantic plant-eaters died out everywhere but Africa at around the same time that the world’s ambush-and-slash sabertooth niche emptied out.

But why did sabercats first go extinct in Africa, the big-game refuge continent where megafauna still exist?

Could these guys have had something to do with it?

wp-1485383968857.jpeg

The oldest known fossils of modern lions were found in Africa, and they are less than two million years ago. Then, around 500,000 years ago, lions apparently spread into Europe and parts of Asia. (Werdelin and others)

By 300,000 years ago, they were common across northern and eastern Asia. At this point, lions also crossed the Bering land bridge into North America and perhaps northern South America. (Werdelin and others)

Some experts wonder whether this had anything to do with the sabertooth extinctions. (Werdelin and others)

It isn’t clear what advantages lions might have had over sabertooths (Van Valkenburgh, 1999; Werdelin and others, but both types of cat do take big prey.

wp-1485383604534.jpeg

It may take several lions to bring down prey that a single sabertooth could handle, but they can do it.

And lions once had the most extensive range of any modern cat in the wild. (Martin, 1980)

Today they can live in forests, woodlands, scrublands, grasslands, and deserts, and they have even hunted seals on the coasts. Lions eat almost any land animal they want and snack on the occasional ostrich egg or other oddity. (AZA)

Their social behavior also changes in response to local conditions (AZA), although we can’t know how this compares to the behavior of sabertoothed cats.

In tough times at the end of last Pleistocene ice age, perhaps this incredible adaptability that lions display today gave them a competitive edge over the sabercats.

Anyway, the arrival of lions seems to match the times that Homotherium and Megantereon disappeared in Africa and Homotherium vanished in Europe.

But in North America, both sabertooth tribes lingered on for tens of thousands of years after lions got there.

It’s a puzzle. Hopefully, further research, with better dating (Stuart), can show what actually happened to big animals at the end of the last ice age.


Images:
Featured image: Lake Baikal icicles, Natalia Kollegova, Pixabay. Public domain.

Mammoth (Mammuthus meridionalis), Museo Paleontologico di Montevarchi. Emiliano Burzagli. CC BY-SA 3.0.

Two lions: Davidsluka, Pixabay. Public domain.

Lions hunting. Corinata, 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.


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