It was once thought that the enlarged upper canines of sabertooths evolved as an adaptation to pierce the skin of “pachyderms” such as elephants or rhinos and other gigantic herbivores of the past. But if we need just one proof against such an argument, then the nimravid Eusmilus should be it.
Members of the genus Eusmilus lived in Eurasia and North America in the Oligocene, millions of years before any true felid sabertooth ever evolved. But if we look at the skull of a well known species, such as Eusmilus bidentatus from France, we find that this early animal had taken its sabertooth specializations to a degree not seen even in the late Pleistocene felid Smilodon. Eusmilus not only had very elongated upper canines, but its whole skull was deeply remodeled to increase the biomechanical efficiency of its killing bite. But, while Smilodon was considerably heavier than even the largest modern cats, Eusmilus bidentatus was… smaller than a modern lynx!

Here is a life reconstruction of Eusmilus bidentatus based on Oligocene fossils from France. The animal was heavily muscled and powerful but with a shoulder height of about 45 cm it was shorter than a modern lynx
eusmilus revised low res

With its modest body size, Eusmilus could not even dream of attacking any of the thick-skinned behemoths that roamed the Oligocene woodlands and prairies, including many kinds of relatives of the rhinoceros. Eusmilus‘ elongated canines meant that, even with the additional gape provided by its specialized mandibular articulation, the clearance between the tips of upper and lower fangs was similar to that of a lynx. The size of the animals to which it could apply its killing bite was consequently rather small. It is thus evident that the sabertooth adaptations of this predator were not aimed at hunting giant, thick-skinned herbivores, but rather to the quick and efficient dispatching of small and medium-sized prey thanks to a killing bite that caused rapid death through massive blood loss, thus minimizing the danger of a trashing prey escaping or wounding the predator, or both.

Another consequence of its small size was that Eusmilus, like many other kinds of small sabertooths through the Tertiary, was not nearly the dominant predator in its environment. For millions of years, hyaenodonts, bear-dogs, and even the omnivorous pig-like entelodons, have abused these sophisticated but small sabertooths, and stolen their rightful prey.

This scene set in the Oligocene of France shows the cow-sized, omnivore entelodontid Entelodon evicting a couple of Eusmilus from their kill
Eusmilus-and-entelodon low res

Small as it was, Eusmilus was not the tiniest sabretooth to evolve. Other species of the genus, like the American Eusmilus cerebralis, was even smaller, and so was the Eocene creodont sabertooth Machaeroides, not taller than a house cat. It is funny to think how nice a pet one of these miniature killers would make, but leaving it to roam in the neighborhood could result in more bloody incidents than any modern house cat can cause…

Want to learn much more about Eusmilus and other mini-sabertooths? Get the award-winning book “Sabertooth” and have your fill of long-in-the-tooth predators! http://www.amazon.com/Sabertooth-Life-Past-Mauricio-Ant%C3%B3n/dp/025301042X/ref=sr_1_1?s=books&ie=UTF8&qid=1454418468&sr=1-1&keywords=sabertooth

Posted on 02/02/2016, in Uncategorized. Bookmark the permalink. 5 Comments.

  1. Sheila Collins

    When I think of Eusmilus, I think of clouded leopards and the smaller subspecies of Panthera pardus. Low-stationed, long-bodied, muscular but agile cats. (I know Eusmilus weren’t “cats”, strictly speaking. But they probably were very catlike in appearance and behavior.) It seems tome that Eusmilus would have been able to take somewhat larger, or at least, more robust prey than Neofelis does. Maybe their prey base was more like the range of prey that modern leopards take & they could avoid some of the kleptoparasitism by larger predators by taking their kills into trees, much as leopards do. That practice works well for leopards. Surely some other cats and cat-like carnivores must have at times evolved similar strategies.

    This is one of my personal favorites of all your illustrations. I love the way you captured the disgusted resignation of the Eusmilus in the foreground.

    • Yes Sheila, it is feasible that Eusmilus bidentatus took larger prey than Neofelis does, although it would certainly not have been a hunter of pachyderms! Taking prey into trees would be a useful strategy, and the skeleton of Eusmilus, although only poorly described, seems to suggest good climbing abilities. But the dentition of Eusmilus was not as well adapted as that of a leopard (with its robust, conical canines)for carrying large prey up trees. With its fragile sabers, Eusmilus would be more comfortable carrying relatively small, light items.

  2. Christian Halliwell

    I was wondering, is there anything you can tell me about Nanosmilus? You only mentioned it in passing in Sabertooth, and it is very difficult to find info on. Also, is it smaller than Eusmilus cerebralis?

    • Nanosmilus kurteni was a diminutive relative of Eusmilus that lived in the Orellan (Early Oligocene) of Nebraska, thus it was earlier than members of the genus Eusmilus. It was described by Larry Martin in 1992 on the basis of a well preserved skull, that shows a relatively primitive morphology when compared to typical species of Eusmilus, such as Eusmilus bidentatus. Nanosmilus did not have such a large mandibular flange or such reduced premolars, among other features. It was about the size of a bobcat (quite a bit smaller than an Eurasian lynx). Nanosmilus kurteni and Eusmilus cerebralis were similar in size.

      • Christian Halliwell

        Thank you for the response, it sounds like quite an interesting animal :).

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