Prehistoric Monkey’s Teeth Showed Ravages of Climate Change

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A capuchin monkey eating a coconut.
A capuchin monkey eating a coconut that could give it cavitiesCredit: Holtocw

Oh good lord, is nobody spared the heartbreak that is dental caries? And was nobody, ever? Now, scientists report finding cavities in the fossil teeth of a prehistoric micro-monkey called Microsyops latidens, which lived and cradled its aching jaw 54 million years ago in Wyoming.

Not only did these prehistoric primates have cavities. A not-small 7.5 percent of the teeth found and identified as Microsyops had them, as an average, which is quite a lot. They are the earliest-known cavities to be found in mammals, Keegan Selig and Mary Silcox of the University of Toronto Scarborough reported Thursday in Nature

It bears adding that the paleontology of malady can have its misleading aspects. Some assumptions haven’t panned out, such as the blanket assumption that when our species stopped roaming and hunting and gathering as a lifestyle, and settled down and grew crops in the Neolithic revolution, our health worsened. Some studies indicate that in the Neolithic revolution we didn’t necessarily get sicker or healthier per se, but our disease burden changed.

One change was indeed more cavities among the early farmers compared with contemporary hunter-gatherers, probably because they ate more starch.

Like us, rats and some other animals, Microsyops was an omnivore, scientists believe. And like ourselves, rats and apparently all other mammals except cats, they had a sweet tooth as well. So, while Microsyops latidens wasn’t farming corn in the Early Eocene and surely ate abundantly of the insects that thronged its arboreal domain, it was eating fructose-laden fruit, Selig and Silcox suggest. And that gave it a lot of cavities.

An image illustrating the cavities in Microsyops.Credit: Keegan Selig

It is true that tooth decay can be caused by things other than sugar, including oral biochemistry, the depth of the fissures in the teeth, and more. But if one is checking fossil monkeys of a specific species in a specific location (Wyoming’s Southern Bighorn Basin), who lived there over millions of years, and if one finds patterns in time, the answer is likely fluctuation in fruit availability.

In short, the team posits that the changes in the prevalence of dental caries over time in the Microsyops set indicate that sometimes they had more sugar-rich foods.

The earliest (56 million years) and latest occurring specimens in the span of 544,000 years that they checked had fewer cavities, averaging about 7.5 percent, as said. But in the middle there was an interval in which 17 percent of the monkeys they checked had cavities. Altogether, the team had 1,030 fossil monkeys – no, not whole – collected over some 50 years to analyze.

The number of individuals was estimated based on the number of teeth they found and some math. One can see the cavities in the ancient teeth using one’s eyes, but they also relied on various scanning techniques.

Unlike fads such as pea foam, fruit doesn’t go out of fashion. Selig and Silcox posit that the primitive monkeys’ teeth are showing the effect of changing climate on vegetation and the availability of fruit. Or other sweet stuff, like certain tree gums; honey will also rot the teeth, if one can find any.

An emperor tamarin monkey, who also has a relatively dismaying propensity to caries Credit: Steve Wilson

How much of a surprise is any of this? Somewhat: The unfortunate Microsyops had more cavities than most simians existing today, with two exceptions – capuchins and tamarins – the team explains.

In Microsyops, 77 out of the 1,030 had cavities (the 7.5 percent), while in tamarins about 9.3 percent have been found to have cavities. Chimps run a rate of about 8 percent. Even mainly frugivorous monkeys such as spider monkeys have lower cavity rates than Microsyops.

Lemurs also dote on fruit but their saliva is unusually basic, offsetting the bacterial acid secretions that rot the teeth.

Capuchins are thought to have high cavity rates because food gets trapped in their teeth more readily than in other monkey species. Bad luck for capuchins. The team speculates that Microsyops had a similar problem.

It should be noted that very little work has been done on tooth decay in extinct mammals, let alone in a species over time. Cancer has been detected in bone lesions in dinosaurs, but not caries per se. One then wonders when flowering plants producing fang-destroying fruit evolved. That may have been contemporaneous with early mammals around 140 million years ago. So, early birds and dinosaurs could have eaten fruit that played hell with their teeth; we just haven’t found the evidence yet.

Tamarins in a tree.Credit: Lucas.Barros / Shutterstock.com

One intriguing study on bears found in the La Brea tar pits in Los Angeles found a lot of cavities in Arctodus simus bears, more than existed in their brethren living farther north in Alaska and Yukon. Conclusion, albeit postulated: the Californian bears had fiercer competition with saber-toothed tigers and the like over meat, and were more omnivorous than their carnivorous northern cousins. Among other things, they resorted to cariogenic fruit.

The bottom line is that fluctuations in climate apparently affected the fruit supply available to Microsyops; when they had more fruit during a period of around 10,000 to 20,000 years, they ate it. When they had less fruit, they adapted.

More than 50 million years after these little proto-monkeys lived in the treetops of Wyoming, we have learned to cultivate food rather than rely on the vagaries of nature. But climate change is already affecting our food supply and we, like little Microsyops, will have to learn to adapt. It’s extinct, by the way. It has no descendants we know of.

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