Broken teeth tell of tough times for Smilodon

When it comes to animals, encyclopedias often present us with generalized descriptions. Where a creature lives, what color it is, what it eats, and other tidbits of information are listed to distinguish one species from another, but what is lost is an appreciation of variation. Be they genetic, anatomical, or behavioral, variations are grist for natural selection's mill, and if you study any species in detail it becomes apparent that individuals differ considerably over space and through time.

This was true of extinct animals just as it is true of living ones. When paleontologists Wendy Binder and Blaire Van Valkenburgh looked at the wear and breakage of dire wolf teeth from the famous La Brea tar pits site in Los Angeles, for example, they found that the specimens from 15,000 years ago damaged or broke their teeth three times as much as specimens from 12,000 years ago. For some unknown reason, it appeared that the older population damaged their teeth by chewing on bones more frequently than the younger population.

But dire wolves are not the only carnivores to be found in the ancient death trap. The saber-toothed cat Smilodon fatalis is represented by numerous specimens, as well, and after their dire wolf study Binder and Van Valkenburgh turned their attention to the most famous of American sabertooths. The result of that study, published in the Journal of Vertebrate Paleontology, suggests that, like the wolves, the cats at Rancho La Brea changed their eating habits over time.

Living cats are hypercarnivores. They eat flesh almost exclusively, but unlike hyenas or dogs they do not often chew on bones. By all indications Smilodon fatalis was also a hypercarnivore, and it has been proposed that it might have been something of a wasteful eater since its overly-large upper canines would have restricted its ability to consume the large animals it killed. With a relatively weak bite force and fragile saberteeth it seemed unlikely that it would risk breaking its teeth by chewing bones.

Yet some populations of Smilodon fatalis may have been more varied feeders than has been appreciated. In 1996 William Anyonge found that the pattern of wear on the canine teeth of the extinct cat differed from that seen in any living carnivores, and the new study by Binder and Van Valkenburgh have added to this by comparing the damage of Smilodon and dire wolf teeth found at multiple La Brea sites.

Since the tar pits were a predator trap (fossils of carnivores outnumber those of herbivores nine-to-one) the scientists had a large sample of Smilodon specimens to work with. What they were looking for were broken teeth with evidence of wear on the fractured surfaces. This would ensure that the tooth had been broken during the life of the animal and not after its death. Altogether they accumulated data on 3,447 dire wolf teeth and 1,955 Smilodon fatalis teeth across three different slices of time.

The scientists addressed the patterns they saw in the two predators in turn. Dire wolves from the 15,360-14,310 year old Pit 13 had a higher rate of tooth fracture than wolves that came before them or after them. This was consistent with what was found in the previous study.

The sabercat teeth reflected a somewhat different pattern. Not only were there more fractured teeth among each of the Smilodon samples, but the highest incidence of breakage was seen in the 22,000-12,600 year old Pit 3. This was not because the animals in one pit were older than another. All of the samples were dominated by young adult animals as ascertained from the development of the pulp cavities within their teeth.

So what was happening to these carnivores? It is difficult to tell. The higher rates of tooth fractures in wolves from Pit 13, in addition to their smaller-than-average size, suggests that the time interval was a stressful time for the wolves when food might have been difficult to get. They would have to make the most of whatever carcasses they could acquire by consuming bone, wearing down and breaking their teeth faster than expected.

Things were different for the populations of Smilodon fatalis. The increased frequency of fractured teeth across all sites (compared to the wolves) may mean that they consumed bone more frequently: they did not just stick to the soft parts like their living relatives. Their teeth were not as well-adapted to this kind of feeding as those of the dire wolves, however. The cheek teeth of Smilodon fatalis were relatively narrow, and that made them much more susceptible to fractures when chewing on bone.

Why the cats were eating bone in the first place may be attributable to competition from the numerous carnivores that inhabited the area. In addition to the dire wolves, Smilodon fatalis living alongside the American lion, the short-faced bear, the sabercat Homotherium serum, and several still-living species of carnivore (such as grey wolves, pumas, jaguars, and bears). Such competition may have caused meat-eating mammals to consume more of each carcass, and so when prey was hard to get predators chewed bones more often.

Despite many restorations that show it as lion-like, Smilodon fatalis was a very different kind of cat. The way it hunted, killed, and consumed prey is still being debated, but what is clear is that it has no equivalent among modern predators. Even more specifically, populations of Smilodon fatalis altered their feeding habits over time. When things got tough, some bit into bone, and I can only wonder what other variations populations of this extinct hypercarnivore exhibited.

Wendy J. Binder; Blaire Van Valkenburgh (2010). A comparison of tooth wear and breakage in Rancho La Brea Sabertooth
Cats and dire wolves across time Journal of Verterbrate Paleontology, 30 (1), 255-161 : 10.1080/02724630903413016