Ancient Teeth Reveal Why Some Mammals Survived While Others Vanished in Southeast Asia

A groundbreaking study published in Science Advances has uncovered why some mammals survived drastic climate changes during the Pleistocene while others disappeared. The key factor, researchers say, lies in ecological flexibility — the ability of a species to adapt its diet and habitat to changing environments.

Led by scientists from the Max Planck Institute of Geoanthropology in Germany, the study reveals that generalist species, which can thrive in varied environments and consume diverse foods, were more likely to survive major climatic shifts. In contrast, specialist species that depended on narrow habitats or specific food sources faced extinction when those conditions disappeared.

The team analyzed 141 fossilized teeth from mammals that once lived across present-day Vietnam and Laos, dating from 150,000 to 13,000 years ago. The fossils included a wide range of species—orangutans, tapirs, rhinos, sambar deer, wild pigs, and macaques.

Using advanced stable isotope analysis—measuring carbon, oxygen, nitrogen, and zinc isotopes preserved in tooth enamel—the scientists reconstructed ancient diets and environmental conditions. Each tooth, in essence, served as a chemical time capsule, preserving information about what the animals ate and the ecosystems they inhabited.

“Teeth are extraordinary biological archives,” said Dr. Nicolas Bourgon, from Max Planck Institute of Geoanthropology. “They tell us not only what animals ate in the past but also how they adapted to sweeping ecological changes.”

By comparing isotopic values among species that survived and those that went extinct, the researchers could infer patterns of resilience and vulnerability across the mammalian community of prehistoric Southeast Asia.

The Pattern: Flexibility Means Survival

The results revealed a stark divide between generalists and specialists.

Species such as sambar deer, macaques, and wild boars displayed broad isotopic ranges, indicating dietary and habitat flexibility. These animals could shift between forested areas and open landscapes, consuming a wide range of vegetation. Their ecological versatility helped them withstand climatic fluctuations and changes in vegetation cover.

In contrast, orangutans, tapirs, and ancient rhinos exhibited narrow isotopic signatures, suggesting highly specialized diets tied to dense tropical forests. As the climate shifted and forests shrank or transformed into savanna-like ecosystems, these specialists struggled to adapt and eventually vanished from the region.

“Specialists often do very well in stable environments, but when ecosystems change, their limited adaptability becomes a major disadvantage,” Nicholas explained in an interview with Phys.org. “That’s why we see them disappearing from the fossil record.”

Orangutans: Once Widespread, Now Confined

One of the most striking cases is that of the orangutan (Pongo). Fossil evidence shows that during the Pleistocene, orangutans roamed far beyond today’s islands of Borneo and Sumatra. They once inhabited much of mainland Southeast Asia.

However, isotope data indicate that ancient orangutans were heavily dependent on fruit from closed-canopy rainforests. As climate variability increased and forest cover retreated, their narrow dietary niche became a liability. Populations dwindled as their preferred food sources and habitats disappeared.

“Modern orangutans can survive by eating bark or leaves when fruit is scarce,” said Nicholas “But their reliance on intact rainforest ecosystems makes them extremely vulnerable. Their history is a warning for what’s happening today.”

Indeed, the study suggests that the same ecological limitations that contributed to local orangutan extinctions thousands of years ago are re-emerging as deforestation and habitat fragmentation intensify across modern Southeast Asia.

While the research focuses on prehistoric species, its implications are deeply relevant today. Southeast Asia currently suffers one of the highest rates of tropical deforestation in the world. Many animals that survived previous climate crises are now endangered by human-driven habitat destruction and global warming.

“The main lesson from this study is that species with narrow ecological niches are the first to disappear when their environment changes,” the authors wrote. “Conservation strategies must prioritize not only population size but also ecological flexibility.”

Maintaining habitat connectivity, the study adds, is essential. As forests are fragmented by agriculture, logging, and urban development, species that require large ranges for foraging or breeding become isolated and less able to adapt. This isolation mirrors the ecological traps that doomed many Pleistocene specialists.

The use of isotopic techniques in this research also provides a valuable tool for modern conservation biology. Similar analyses could help scientists predict how today’s species are responding to environmental pressures—offering early warnings before irreversible declines occur.

A Warning from the Past

As global temperatures rise and ecosystems transform at unprecedented speed, the findings serve as a stark reminder: adaptability determines survival.

“Today’s species are facing the same kind of environmental pressures as mammals did during the Pleistocene,” said Nicholas. “Those that can adjust their diets and habitats will persist. Those that cannot, may vanish forever.”

The study’s message extends beyond wildlife. It highlights the delicate balance between organisms and their environments—a relationship that defines resilience in the face of planetary change.

Protecting biodiversity, the researchers argue, is not just about preserving species numbers but about safeguarding the ecological and behavioral diversity that allows life to endure disruption. Without it, the next great extinction could unfold not over millennia, but within generations.

From a handful of fossilized teeth, scientists have reconstructed a story of adaptation, collapse, and survival spanning tens of thousands of years. Their findings bridge the ancient and the modern, showing that the past holds crucial lessons for the future.

As Nicholas concluded, “The fossils remind us that evolution favors flexibility. If we ignore that lesson, both wildlife and humanity will pay the price.” (Wage Erlangga)