Ancient teeth reveal why some animals survived climate change

A new study tested a simple idea with hard evidence from ancient teeth. Over 141 fossil teeth from Vietnam and Laos, spanning roughly 150,000 to 13,000 years, show that mammals with flexible diets and habitats tended to persist as climates swung.

Generalists coped, but specialists often did not. That is the core finding of the research, and it comes from chemical signals sealed into tooth enamel that track what animals ate and where they foraged.

What ancient teeth record

Dr. Nicolas Bourgon of the Max Planck Institute of Geoanthropology (MPI) led the international team that carried out the work.

Tooth enamel preserves traces of stable isotope, variants of an element measured by mass that reveal food and water sources. One source of insight is enamel-bound nitrogen, nitrogen trapped inside tooth enamel that can shift with an animal’s place in the food chain. 

The team also tracked δ66Zn, the ratio of zinc isotopes used for diet reconstruction, which tends to be lower in carnivores and higher in herbivores.

Earlier work confirmed that zinc in enamel can sort carnivore, omnivore, and herbivore signals even when other tissues fail.

Together, these enamel signals map feeding habits without needing collagen, which often decays in tropical caves. That opens a window on species that left only teeth behind.

Ancient teeth and survival

The fossils come from caves in northern Vietnam and northeastern Laos. They cover colder and warmer phases across the Late Pleistocene, a natural test of how species responded as environments changed.

The researchers measured carbon, oxygen, nitrogen, and zinc isotopes in the same teeth to separate habitat from diet.

The team also compared species that still live in the region to those now extirpated, locally extinct in a particular area though surviving elsewhere.

The result is a time series of diets and habitats before, during, and after climate swings. It shows which species shifted foods or foraging places and which stayed locked into narrow niches.

Who survived and why

Macaca monkeys, wild boar, and sambar deer showed broad isotopic ranges. That pattern matches animals able to switch foods or forage in more than one setting.

By contrast, the teeth of orangutans, tapirs, and rhinoceroses indicated tight isotopic ranges.

Orangutans, in particular, kept values consistent with fruit from closed-canopy forest, which has dense leaf cover that limits sunlight to the ground. That narrow niche matched their modern needs.

Context raises the stakes. Southeast Asia is a major deforestation hotspot, which heightens risk for specialists tied to intact forests. A 2019 regional assessment found the region among the world’s most intense hotspots for forest loss, with large implications for biodiversity and carbon.

How chemistry helps

Enamel nitrogen and zinc answer different questions. Nitrogen tracks trophic level, helpful for separating plant eaters from meat eaters and for clarifying omnivore diets. Zinc refines those dietary splits and can indicate the kinds of plants eaten.

When the two are combined with carbon and oxygen, you can tell whether an animal changed its diet, changed its habitat, or both. That matters for conservation because the path to persistence may be flexibility in food, flexibility in space, or a mix of the two.

The study’s dataset shows that species with living relatives in the region tended to show one or more of those flexible responses. That pattern does not guarantee future survival, but it gives managers a measurable trait to track.

Teeth signals in orangutans

The enamel signals suggest orangutans in mainland Southeast Asia stuck with forest fruits over thousands of years. They could broaden foods when fruit dipped, yet they still relied on forest.

Modern population trends echo the risk. Between 1999 and 2015, more than 100,000 Bornean orangutans were lost, much of it linked to habitat change and killing outside clearing zones. Stable populations today typically occur where significant forest cover remains.

Those parallels do not reduce every species to a single rule. The enamel data show that some mammals broaden diets in wetter, denser forests, while others broaden diets when forests open and seasonality rises. Flexibility is context dependent.

Interpreting ancient teeth

The team normalized data where geology nudged zinc baselines and checked nitrogen against enamel nitrogen content to rule out contamination.

The experts matched patterns across sites with similar faunas, which makes cross site comparisons credible.

No single isotope tells the whole story. The gain comes from stacking independent proxies with different strengths, then asking whether the directions agree. 

“We underscore the precariousness of certain species,” wrote N. Bourgon, after comparing dietary ranges across extinct, extirpated, and surviving taxa.

Ancient teeth and climate shocks

The results of the study turn chemistry into a map of ecological options. Animals that could take more than one route through that map had a better shot at lasting through climate jolts.

That same logic applies to today’s conservation planning. Protect food webs, not just names on a list, and keep habitat mosaics that give animals room to switch.

Collecting enamel data from living populations will help calibrate how flexibility varies by season and place. Matching enamel records to modern monitoring can turn the fossil insight into a present day tool.

The work also points to places where small changes could pay off. If a species shows dietary flexibility but narrow habitat use, keeping forest corridors connected can unlock that flexibility.

The study is published in the journal Science Advances.

Image Credit: Dr. Nicolas Bourgon

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