Have you ever gone out to a buffet with friends or family? There are all sorts of savory and sweet options laid out for you to arrange to your personal tastes, whether it's a plate piled high with olives or just one prawn, thank you. The point is that we all have our gustatory desires and so we choose differently from the options assembled in front of us. It turns out that extinct American mastodons did the same.
Breakdowns of how prehistoric animals lived are often organized like trading card stats – where they lived, how long ago, and what they ate. It’s a kind of reductionism that obscures the squishiness of life into something that’s more easily digestible for communicating science. But the fact is that American mastodons were variable animals – just as we are – and so simply calling them Ice Age forest browsers is about as helpful as calling sabercats carnivores. We need to increase the focus to understand their ecology, and, by analyzing pits and scratches on Mammut americanum teeth, that’s what paleontologists Jeremy Green, Larisa Desantis, and Gregory Smith have done.
When American mastodons were tromping around the Pleistocene, the foods they ate left tell-tale marks on their teeth. Conifer branches, osage oranges, and other mastodon fare scratched and pitted the bumpy molars of these elephants. And by comparing the scratch patterns of extinct animals with living animals with known diets, paleontologists can parse what ancient species were likely eating. In particular, tiny signs of damage – termed microwear – record what a particular animal was eating close to the time it died. That’s what Green and colleagues looked at in their new study, analyzing the microwear of 65 Mammut americanum teeth from six different localities across the midwestern and southern portions of North America.
In broad strokes, the new analysis reinforced what paleontologists knew from gut contents, coprolites, and geochemical signatures. American mastodons were browsers, elephants of the forest rather than the grassland like their distant mammoth cousins. But not all mastodons were eating the same thing. The microwear on southern American mastodons in Florida, Green and coauthors point out, are more consistent with plants that were softer but tougher – rather than harder and more brittle – than those elsewhere. The mastodons of the Florida cypress swamps were subsisting on a different selection of browse than their relatives in boreal forests or pine parklands, their choices perhaps influenced by sharing their habitat with other large browsing mammals from deer and tapirs to giant ground sloths.
And while it might sound contradictory, a lack of change further underscores that American mastodons were flexible. Included in the sample of 65 teeth were mastodon fossils from two different time periods in Ice Age Missouri. The local habitat changed between the two temporal spans, moving from a more open, pine-dominated parkland to a boreal forest full of spruce. Yet there doesn’t seem to be any change in the microwear of mastodon teeth. Jack pine and spruce are similarly hard, the researchers point out, and so the mastodons kept happily chewing along even as the environment shifted.
The upshot of all this is something that modern zoologists are likely to be familiar with. “Our findings are significant in that they reconstruct M. americanum as a species with adaptability in its browsing strategy across its range," Green and colleagues write, "with regional populations able to maintain their diet in the face of local environmental shifts in the Late Pleistocene.” In other words, American mastodons were not locked into a narrow niche but were flexible, variable animals that were part of a broad population. We often forget this when dealing with fossil species, narrowing down to particulars because of a limited sample size. It's worth keeping in mind as we look to the past. Mammut americanum was a variable and resilient creature, and that makes the beast's disappearance all the more mysterious.
Green, J., Desantis, L., Smiths, G. 2017. Regional variation in the browsing diet of Pleistocene Mammut americanum (Mammalia, Proboscidea) as recorded by dental microwear textures. Palaeogeography, Palaeoclimatology, Palaeoecology. Doi: 10.1016/j.palaeo.2017.08.019