The Many Lives of Smilodon

On a superficial level, the predatory habits of the saber-toothed cat Smilodon would not seem to be especially mysterious. Traditionally – and incorrectly – restored as a lion with extra-long upper canines, this felid obviously used its fearsome dentition to dispatch the large prey of its Pleistocene heyday.

Of course, things aren’t as simple as that. The function of Smilodon teeth and the mechanics of its bite have long been debated by paleontologists, but ideas about its habits have never been as varied as they were around the turn of the 20th century. William Diller Matthew, an expert on fossil mammals at the American Museum of Natural History, documented some of the long-lost ideas about Smilodon by frustratedly dismissing them in his own works. In his 1901 monograph Fossil Mammals of the Tertiary of Northeastern Colorado, for one, Matthew mentioned several ideas which today seem ludicrously fanciful.

The first, and the most long-lived of the bunch, was the idea that the teeth of Smilodon had been produced by an unstoppable, internal evolutionary trend which caused them to overdevelop. Taken by some scientists as a sign of a lineage in decline, the argument was that the teeth of the cats grew so long that they could no longer open their mouths and so they starved to death. Matthew rightly recognized that this idea was nonsense. Saber-toothed cats persisted for a long time in the fossil record and showed no sign of evolving to excess. Furthermore, Matthew differed from many of his colleagues in considering natural selection to be an important driver of evolutionary change. Viewed from a Darwinian perspective, it didn’t make sense that Smilodon would evolve itself into extinction. As Matthew put it, “it is impossible to believe that any innate tendency to evolution – if such exists – could so far overcome the repressive influence of selection as to produce finally a race that would be self-extinguishing.”

This wasn’t even the silliest of the ideas about Smilodon. After discarding the suggestion that Smilodon attacked its prey by stabbing at it, close-mouthed, with the tips of its canines, Matthew exclaimed “The suggestion has also been made that the tusks were useful in climbing trees!” The notion was utterly preposterous. The blade-like teeth of the Smilodon were totally unsuited with dealing with the stresses of climbing, and any cat that tried to use their teeth as crampons would either become stuck or break off their teeth in the process.

Likewise, Matthew criticized the proposal that Smilodon was aquatic. This notion had been based upon the resemblance of its canines with the long tusks of the walrus. The idea could not be disproved, Matthew stated, but the overwhelming lack of positive evidence for it made it wise to relegate the hypothesis to the junk heap of idle speculation. At the very least, it was difficult to visualize how Smilodon might hunt while submerged since its dentition “would hardly be the most effective weapon for capturing an agile prey in the water.” (This did not stop the author of the terrible novel Fatalis from including a scene in which a Smilodon attacks and dispatches a sailboat full of hapless teens, however.)

Unfortunately, Matthew did not have future historians of science in mind when he wrote his criticisms. He did not list any paleontologists who espoused the views he mentioned and he did not include any source citations. Given that other authorities – such as marine mammal expert Remington Kellogg – later cited Matthew’s work directly instead of the original sources, this problem was never rectified.

I dug around through the literature in an attempt to track down the sources of these ideas. I did not have very much luck, but I did happen across one curious passage written by one of Matthew’s peers. In an extensive review of dental anatomy included in the 1886 volume The American System of Dentistry titled “The Comparative Anatomy of the Teeth of the Vertebrata“, the paleontologist Jacob Wortman held forth on the habits of Smilodon. Doubting that Smilodon could have opened its mouth wide enough to bite anything, Wortman wrote “Seeing that in the existing cats their chief destructive powers reside in their biting qualifications, it is difficult to understand how [Smilodon] inflicted wounds sufficient to destroy their prey, unless they did so with that part of the tusk which projected below the level of the symphysis when the mouth was closed, just as the walrus uses his tusks to clamber over the ice. They may also have been used to assist the animal in climbing, and in this way attained their great size.”

Wortman’s review may have been one of the sources of Matthew’s criticisms, and Matthew may have been familiar with Wortman’s ideas on a more informal basis. As shown by the bibliography of Matthew’s 1901 monograph, just two years earlier he had published a paper on “The Ancestry of Certain Members of the Canidae, the Viverridae and Procyonidae” with Wortman. Given their collaboration, it is possible that Matthew and Wortman discussed the natural history of Smilodon at some point, though I have no direct evidence of such a conversation. Perhaps Matthew felt compelled to criticize some of the ideas of his colleague without dragging Wortman’s name into it, although not all the ideas Matthew criticized are attributable to Wortman. I am still in search of the document which cast Smilodon as a rapacious aquatic predator which skewered its prey.

Today the predatory behavior of Smilodon remains difficult to reconstruct. There are no modern saber-toothed predators of its kind for comparison. Even so, the emerging picture is that this sabercat grappled its victims into submission. Although the impressive teeth of Smilodon have traditionally received the most attention, a 2007 study by Colin McHenry and colleagues found that this cat had a relatively weak bite. Compared to that of a lion, the skull of a Smilodon simply couldn’t handle the large amounts of stress created by a large, struggling animal and so it is improbable that Smilodon attacked with its teeth first. Instead, as confirmed by a study published this year by Julie Meachen-Samuels and Blaire Van Valkenburgh, Smilodon probably used its exceptionally powerful forelimbs to wrestle prey to the ground before delivering a fatal bite to the soft, vulnerable throat. This strategy certainly makes sense given the anatomy of Smilodon, but explicitly visualizing how one of these formidable sabercats would have attacked a juvenile mammoth or a giant bison still requires as much imagination as hard science.

Top Image: A sketch of the head of Smilodon by Charles R. Knight. From Matthew, 1901.

References:

McHenry, C., Wroe, S., Clausen, P., Moreno, K., & Cunningham, E. (2007). Supermodeled sabercat, predatory behavior in Smilodon fatalis revealed by high-resolution 3D computer simulation Proceedings of the National Academy of Sciences, 104 (41), 16010-16015 DOI: 10.1073/pnas.0706086104

W.D. Matthew (1901). Fossil Mammals of the Tertiary of Northeastern Colorado Memoirs of the American Museum of Natural History, I (VII)

Meachen-Samuels, J., & Van Valkenburgh, B. (2010). Radiographs Reveal Exceptional Forelimb Strength in the Sabertooth Cat, Smilodon fatalis PLoS ONE, 5 (7) DOI: 10.1371/journal.pone.0011412

Wortman, J. 1886. “The Comparative Anatomy of the Teeth of the Vertebrata” in The American System of Dentistry, Vol. I. Philadelphia: Lea Brothers & Co.