How Extinction Changed the Coyote

The La Brea asphalt seeps are famous for the predators found entombed there. Dire wolves and the sabercat Smilodon – the site’s mascot – are the exotic Ice Age stars that everyone comes to see. The third most-numerous carnivore found there doesn’t enjoy such celebrity. If you follow the path of the Page Museum around its circular path, there’s a little alcove near the end that presents some modern animals that lived in Ice Age times. And there, howling before an artistic depiction of itself, is that third most-abundant carnivore – the coyote.

Coyotes are familiar canids. Not only are they common, but they’re so ecologically flexible that they’ve actually taken up residence with us. Compared to a dire wolf or sabercat the coyote seems familiar and plain, but it would be a mistake to overlook the beast. Coyotes are survivors of the Ice Age, and their bones record tales of evolution and extinction.

Des Moines University paleontologist Julie Meachen started to draw out some of these details in a 2012 study on coyote body size. Ice Age coyotes – such as those found at La Brea – were larger than their modern counterparts, and this was often attributed to the idea that a larger body would’ve helped the carnivores better conserve body heat during the Ice Age. But Meachen fand coauthor Joshua Samuels found that this wasn’t the case.

By comparing coyote changes with alterations in gray wolf body size, Meachen and Samuels found that climate change couldn’t account for the shrinking coyotes. Instead, Ice Age coyotes may have been larger because size was an advantage during a time when there was a broader guild of big predators stalking the land. Once the dire wolves, sabercats, and American lions went extinct, competition for prey ceased to be so intense and coyotes became smaller. Also, many of the large prey animals of the Ice Age – such as horses and camels – went extinct, too, meaning less food on the hoof for coyote packs.

Now Meachen and team of collaborators have followed up on the body-size study with an investigation of coyote mandibles from the Ice Age to the present. The researchers drew from three pools of coyote remains  – 29,000-13,000 year old Ice Age jaws; 10,000-8,000 year old Holocene jaws; and modern jaws – and created 2D models of each jaw to track how certain landmarks varied between individuals and through time.

The results buttressed the conclusions of the previous study. Ice Age coyotes were generally larger and more carnivorous than their modern counterparts. The evidence is in the killing and cutting part of the jaw. The shearing portion of the Ice Age coyote tooth row was longer and underlain by a deeper, more robust portion of jaw bone, while the grinding portion of the tooth row was shorter compared to today’s modern, more omnivorous coyotes. The Holocene coyotes were intermediate in form, befitting their placement in time between the two.

Along with the sheer number of specimens found at La Brea and tooth wear that indicates gnawing on bone, the new evidence adds to the emerging picture of larger, more carnivorous Ice Age coyotes that likely worked in groups to bring down large prey, as well as defend and steal carcasses. So why have coyotes shrunk with time? Meachen and colleagues suggest that the disappearance of other carnivores and the rise of gray wolves was crucial.

Gray wolves were present in North America during the Ice Age, but they were relatively rare compared to dire wolves. Once dire wolves and some of the other large Ice Age carnivores went extinct, however, gray wolves were able to gain more of a foothold. This was bad news for the coyotes. Modern gray wolves often kill large coyotes, and the same was likely true in the wake of the end-Pleistocene extinction. As a result, Meachen and colleagues propose, the wolves put increased pressure on coyotes to become smaller and adapt to a lifestyle of pouncing on smaller prey.

The end-Ice Age extinction was not just about loss. It also opened up new possibilities and interactions that have been affecting the survivors for the past 10,000 years. So the next time you see a coyote loping through the sagebrush or even stealing a snack from a garbage can, stop a moment to appreciate the adaptable nature of a canid that has changed with the times.

Reference:

Meachen, J., Janowicz, A., Avery, J., Sadleir, R. 2014. Ecological changes in coyotes (Canis latrans) in response to the Ice Age megafaunal extinctions. PLOS ONE. 9 (12): e116041. doi:10.1371/journal.pone.0116041