Bears and Sabertooths: opposites living side by side
I recently had the luck to watch the endangered spanish brown bear in the wild, and this experience has made me think a little about the evolution and adaptation of bears, and their coexistence with sabertooths.
Bears and sabertooth cats have been living side by side for many million years. A very early example is the amazing fossil site complex of Cerro Batallones in Madrid. Batallones is a hill where several fossil sites of similar age have been found, and each of these sites is what remains of a cavity which acted as a natural trap during the late Miocene, some 10 million years ago. At one of those sites, called Batallones 3, the remains of many sabertooth cats of 2 different species (Promegantereon ogygia and Machairodus aphanistus) have been found, together with those of several other carnivore species, including a large bear: Indarctos arctoides.
For some reason, the bear is completely absent in other sites such as Batallones 1. But in Batallones 3 it is pretty abundant, and it seems that, like the other carnivores at the site, it came here to scavenge on the remains of other victims of the trap. Meat is such a magnet for carnivores that it attracts species with very different diets, and not only the kind of animals that today we know as scavengers. Large hyenas with dentitions adapted to bone cracking, such as the ones living today in Africa and Asia, were absent in the Batallones faunas, and in fact none of the species that we find at the sites is nearly as specialized as modern hyenas for efficient scavenging.
But if we concentrate on the two kinds of predators mentioned in the title of this post, we find that while none of them is a specialized scavenger, their inferred diets were as different as can be for two carnivores.
The sabertooth cat was an extreme hypercarnivore: its carnassials (the pair of teeth that act as scissors and are used by carnivores for cutting meat) were enormous and extremely blade-like, and the rest of the cheek-teeth (or postcanine dentition) were either blade-like, or extremely reduced, or lost. This means that the dentition of the sabertooths served for little purpose other than processing the meat of large prey. Bone-cracking or crunching vegetable matter were nearly impossible.
Bears, on the other hand, are essentially omnivores with multi-purpose dentitions. They have a collection of wide, blunt premolars and molars which can grind plant material, crush bones or cut meat according to what is available. They are not extremely efficient in any of these actions but are reasonably good at all of them. Perhaps their greatest strenght would be vegetarianism, but they are mere amateurs compared to, say, ruminants. Indarctos, the bear found at Batallones, was more primitive than its modern relatives in several ways, but essentially it was already a very recognizable bear.
One important advantage of the bear dentition is its potential for adaptation to changing conditions. From something not very different from a modern brown bear (in terms of diet and habits), evolution produced the giant panda over the course of a few million years, as an adaptation to a diet mostly composed of bamboo. Even more surprising, a member of the brown bear lineage evolved, over the course of a few millennia, to give rise to the polar bear, an animal that feeds almost exclusively on meat. It is certain that, when faced to the kind of pressure that led those bear lineages to such radical dietary shifts, a large sabertooth cat would respond very differently. To put it simply: it would go extinct.
Here is a reconstruction of Indarctos, shown to the same scale as that of Machairodus, both based on fossils from Batallones
As two kinds of carnivores of broadly similar body size, Machairodus and Indarctos would not be especially happy to meet each other at Batallones. Getting together around carcasses, as they may have done on ocassion, would have been a tense situation. But for most of the time, their different diets and lifestyles allowed these animals to stay away from each other and avoid direct competition. Such was the case with later species of bears and sabertooths in the following millions of years, until one of the two lineages disappeared from the Earth at the end of the Pleistocene.
But let us now return to the present day, back in the Asturian mountains. Bear observation here is a real privilege, since only a few years ago these animals were on the very edge of extinction in Spain and you could hardly expect to see one in the wild, no matter how many hours you spent looking for it. But once you get to see them (usually quite far away and looking through a telescope), it may be a bit disappointing to see that all they do is graze on the fresh grass, almost like the chamois herds that share those mountains with them. But as we watched a young, yearling bear walk down a steep hill side, it casually approached a chamois herd. And the herd did not react as they would do at the approach of a fellow ruminant. They got pretty nervous and kept their distance, while trying not to lose sight of the bear. In sum, they reacted as they would do in front of a predator. The bear may spend most of its time grazing, but it does not deceive the true herbivores around it. They recongnize a potential predator when they see it, be it a sabertooth or a bear!
You can watch the video following this link: