Carnivorous Neighbors — How Sabercats and a Bear Dog Managed to Coexist

Prehistoric predator traps are wonderful things. From the Allosaurus-dominated bonebed at the Jurassic Cleveland-Lloyd quarry in eastern Utah to the dire wolf and Smilodon-filled graveyard of Los Angeles, California’s La Brea asphalt seeps, predator-rich fossil deposits provide paleontologists with a wealth of information about animals that were relatively rare in the habitats they stalked. After all, an ecosystem can only carry so many large carnivores. Any site containing multiple individuals of an apex predator is a bonanza for researchers.

Another such site, the focus of a new Proceedings of the Royal Society B study by University of Michigan paleontologist Soledad Domingo and colleagues, is entombed within the 10- to 9-million-year-old rock at Cerro de los Batallones in Spain’s Madrid Basin. Paleontologists working this locality have found at least nine different assemblages of large fossil mammals, and two of these deposits are exceptionally rich troves of carnivore bones.

Out of 1,800 large mammal fossils recovered at one of these sites, about 92 percent belong to 10 different species of carnivorans of various size. There are the remains of small cats, skunks, a civet-sized hyena, and a red panda relative, but the bonebed is especially abundant with the vestiges of three apex predators that lived alongside one another. In addition to a pair of sabercats – the leopard-sized Promegantereon ogygia and the tiger-scale Machairodus aphanistus – there lay the bones of the large, heavily muscled bear dog Magericyon anceps.

None of these large Miocene carnivores have living descendants, or even modern analogs. We can only approach the hunting habits of these species through the fossil record and the limits of scientific imagination. This leaves us with a mystery – how did these three ancient carnivorans manage to coexist? To investigate that question, Domingo and co-authors drew upon geochemical clues they drilled out from the teeth of the carnivores and their potential prey.

The stable isotope δ13C is what the researchers were after. As herbivores eat plants, chemical signatures in the form of δ13C become incorporated into their teeth and bones. Paleontologists often use these values to estimate what kind of habitat a creature lived in, from open grasslands to dense forests. Carnivores preserve these traces, too. When a sabercat or bear dog consumed the muscle and bone of their prey, elements of the herbivore’s δ13C profile became locked in the carnivore’s tissues. By comparing the δ13C profiles of the three carnivores with those of the herbivores they lived alongside – from rhinos, an elephant, and a giraffe down to horses, a pig, and an antelope – Domingo and collaborators were able to estimate which animals frequented particular habitats and therefore which prey species were suitable candidates for each of the carnivores.

Despite their difference in size, the two sabercats seemed to prey on medium-to-small herbivores that frequented relatively closed, wooded areas. Based on the similarities of their δ13C results, it appears that the cats might have often dined on prehistoric pig, although the authors note that the leopard-size Promegantereon ogygia might have gone after even smaller prey that was not sampled in the study.

Frustratingly, the results only indicate that the sabercats inhabited forests and relied on similar prey, but both were distinct from the bear dog. Magericyon anceps, the researchers propose, prowled more open spaces and often ate antelope and musk deer (not included in this study, but known from partially digested remains supposedly left by a bear dog). Being of similar size, perhaps the bear dog and Machairodus aphanistus avoided each other by preferentially hunting in slightly different habitats.

Despite their predatory acumen, the three carnivores probably didn’t eat the rhinos, elephant, or giraffe that browsed the same woodlands. Sheer size shielded the megaherbivores, although the same species would have been vulnerable when young, elderly, or infirm. And while Domingo and co-authors doubt that the carnivorans regularly scavenged, the sabercats and bear dog obviously had some interest in rotting meat. If they didn’t, then they wouldn’t have been attracted to the carrion reek of the predator trap that ultimately killed and preserved them.

References:

Argot, C. 2010. Morphofunctional analysis of the postcranium of Amphicyon major (Mammalia, Carnivora, Amphicyonidae) from the Miocene of Sansan(Gers, France) compared to three extant carnivores: Ursus arctos, Panthera leo, and Canis lupus Geodivertistas, 32 (1), 65-106

Domingo, M., Sanchez, I., Alberdi, M., Azanza, B., Morales, J. 2012. Evidence of predation/scavenging on Moschidae (Mammalia/Ruminantia) from the Late Miocene of Spain. Lethaia. 45, 2: 386-400

Domingo, M., Domingo, L., Badgley, C., Sanisidro, O., Morales, J. 2012. Resource partitioning among top predators in a Miocene food web. Proceedings of the Royal Society B. doi: 10.1098/rspb.2012.2138