Xenosmilus is the grittier name for “cookie-cutter panda cat”

It sounds cute and looked more like a bear, but its main hobby was blood-letting.

The more observant among you will have noticed its impressive grin too. Xenosmilus was one of the “true” sabre-tooth cats, descended from the terrifying Machairodus or “knife-tooth”, which followed a separate evolutionary branch to modern day lions and tigers.

Until Xenosmilus came along, moggies of the Machairodontinae were divided into three tribes.

Now, there’s a fourth, and for some, even an implied fifth. Leaving aside the Metailurini crowd, which is sort of a holding pen for species that both do and don’t fit into the others, there are two main races.

First off, there are the dirk-toothed cats (Smilodontini), which are stout, bulky ambush predators with long canines, named after sabre-tooth poster child Smilodon.

The second race are the scimitar-toothed cats (Homotherini), which have shorter canines, but longer, slender limbs for chasing down prey, named after Homotherium.

After about a decade of being tossed in a pile with the scimitar-toothed lot, Xenosmilus was re-examined in the 1990s and gave way to an entirely new family: one that was stout and bulky, but with short fangs. Don’t let the latter point fool you though, because unlike its relatives’, all of Xenosmilus’ teeth, not just the fangs and incisors, were serrated.

That’s troubling enough news for a prey animal, but ‘Smilus took it to another level.

Since its top teeth lined up a certain way, and it had a more powerful bite than the scimitar-toothed lot, it could concentrate its bite force on just two teeth at a time, helping to slice right through hide that was tough, woolly or both.

It would also leave a characteristic, semi-circular bite mark, hence “cookie-cutter cat”. It doesn’t sound anywhere near as tough as “dirk-“ or “scimitar-“ though.

So was this something that early humans had to worry about?

Well, Xenosmilus snuck and stalked its way through the woodlands of Florida about 1-2 million years ago, and thanks to a warm climate all year round, there were plenty of trees and other cover for it to hide in. And plenty of trees and foliage attracts plenty of bulkier, slower prey, such as mammoth-wannabe mastodons.

It was a lush land unsullied by humans, who wouldn’t arrive for another 75,000 years, but I’m sure if they’d have been around, they’d have swapped stories over who got the most circular scars. That was if they didn’t drop dead from shock first.

Being on the beefier side, Xenosmilus had a couple of options for bringing down its prey.

After ambushing and taking a huge meaty chunk out of it, it could wait for it to die from blood loss or totter along behind it until it did. Alternatively, as Dr. Virginia L. Naples put it, it was the “sumo wrestler” of the sabre-tooths, with the size and proportions of a modern panda.

Thanks to a large psoas major muscle, and limbs stronger and stouter than a bear’s, it could grapple prey while stood on its hind legs. It probably drooled a lot while doing so, because your lips need to be stretchy to accommodate 9 cm (3.6 inch) fangs, even when you’re not mid-bite.

Its remains, and that of its prey, might give us a hint about its social life too.

This is based on a sample of two, so it’s possible we found the only weird couple in amongst thousands of other available Xenosmilus. But the partial skeletons found in a Florida quarry back in the 1980s were in “hog heaven” – an area full of peccary (small pig) bones. It’s possible that this was their den, and they hunted together before bringing their prey back. Another theory nudging in the direction of it being a social mammal is the use of its fangs. Perhaps it also used them to impress, intimidate or communicate, like modern deer antlers? They were pretty prominent, so why not?

Another mystery is why it went extinct.

As I mentioned earlier, there were no humans around to spoil the party, and Smilodon – our classic sabre-tooth – flourished once Xenosmilus was out of the picture, so it wasn’t through lack of prey or suitable hunting territory. It may have been good old fashioned competition between the two, as they had similar hunting styles and were evenly matched size-wise.

We won’t know until we find more remains, and there have been murmurs of Xenosmilus, or an extremely close relative, prowling about in Uruguay around the same time, so maybe it was more widespread than thought. The chances of finding more remains just went up a notch, then! Maybe it’ll also open the door to a fifth tribe, one with long fangs and long legs? I think a speeding sabre-tooth would probably drive most things to extinction.

 

TLDR

Name meaning: Xenosmilus hodsonae – “Hodson’s strange blade”, named after Debra Hodson, the wife of one of its researchers.

What? Stocky and extinct sabre-tooth cat with a distinctive bite.

Where? Southeastern North America, about 2.5-1.5 million years ago during the Pleistocene period.

How big? About 1.5-1.8 metres / 5-6 feet long.

Probable motto: At least my bite marks look neat.

 

Just to prove I’m not fibbing:

Choi, Charles Q. 2011. “Ancient sabre-toothed cat drooled like a Saint Bernard“. Live Science.

“Fossil find rattles sabres“. 1999. BBC News.

Green, Jeremy L. et al. 2005. “The deciduous premolars of Mammut americanum (Mammalia, Proboscidea)“, Journal of Vertebrate Paleontology 25(3):702-715.

Gugliotta, Guy. 2013. “When did humans come to the Americas?” Smithsonian.com.

Harrington, Ariana. 2015. “Xenosmilus hodsonae“. Florida Museum.

Naples, Virginia L. et al. 2011. “The other saber-tooths“. John Hopkins University Press.

Perkins, Sid. 2011. “A most fearsome saber-toothed cat“. Science News, via Carnivora.net.

Strauss, Bob. 2017. “Saber-toothed cat pictures and profiles“. Thoughtco.com

Strauss, Bob. 2019. “Xenosmilus, another prehistoric North American cat“, Thoughtco.com.

Wang, Xiaoming. 2012. “A Review of ‘The other saber-tooths, scimitar-tooth cats of the Western Hemisphere‘”, Journal of Vertebrate Paleontology 32(4):981-982.

 

Featured image credit: “Xenosmilus – top saber”, by RAPHTOR.