October 6, 2022

17 17-million-year-old teeth open windows on early apes and human evolution

17 17-million-year-old teeth open windows on early apes and human evolution

An international team of scientists has shown in a new study that fossilized mammal teeth can provide insights into the role and behavior of seasonal climates in the evolution of humans and mammals.

This study examined oxygen isotopes in teeth from a 17-million-year-old site in the Turkana Basin in northwest Kenya. These included the teeth of a mysteriously sized monkey known as Afropithecus turcanensis. Research It was recently published At Proceedings of the National Academy of Sciences,

To put the fossils in context, the researchers also measured oxygen isotopes in the teeth of modern mammals from across tropical Africa and analyzed the isotopic signals they produced. The team, led by Daniel Green, a postdoctoral scientist at Columbia University’s School of Climate, and Tanya Smith of Griffith University in Australia, found that modern oxygen isotopes (natural forms of oxygen that differ by mass) detail rainy and dry seasons, the environment They record life. Conditions such as altitude and vegetation and changes in mammal behavior.

The arid and fossil-rich landscape of Kalodirr in the Turkana Basin region of Kenya was once the forest home of ancient monkeys. Afropitcus 17 million years ago Photo: Suzanne Cote

In modern teeth, the researchers found that teeth can even show human changes to the natural landscape, such as damming a river, and document certain meteorological events. Measurements of modern ape teeth recorded a prolonged drought in one case in Ethiopia and a heavy rainfall event in another in Uganda. Working with primatologists, the researchers were able to determine that teeth were formed when these climatic events occurred.

With the context provided by modern primates, the authors then analyzed the teeth Afropitcus It was found on a site called Kalodirr and compared its results to 17-million-year-old precipitation patterns simulated by climate models.

The researchers showed that ancient apes experienced dry and wet seasons of varying intensity over time, likely influenced by natural changes in Earth’s orbit around the sun. The results also showed that the jaw’s specialized adaptations—thick enamel and strong masticatory muscles—could help. Afropitcus During seasons of drought or lack of resources, eat solid foods.

“The impact of climate change on the earliest African apes is poorly understood because detailed records of seasonal changes from this early period, the Miocene, are more sparse,” says Green. “Oxygen Isotope Compositions of Afropitcus And near-herbivores show that the behavior and anatomy of apes in this part of East Africa were shaped by seasonal environments long before the emergence of hominins.

The lead author, Daniel Green, reviews the fossil material of Kenya’s Turkana Basin.

Another key finding of the team’s research is that studies of oxygen isotopes in fossil hominins—our ancestors—have so far underestimated the chemical changes in their teeth. For this reason, it has been difficult to estimate how their behavior might vary by season in the African savannahs.

The research “has broad significance because seasonal changes in resource availability are thought to have influenced the evolution of great apes, early humans and modern humans,” Smith said.

The study used innovations in high-resolution chemical measurement techniques led by Ian Williams of the Australian National University, who was an author on the paper. Teeth grow in microscopic temporal increments similar to tree rings, but during childhood, tooth increments form daily rather than annually. So with the innovations provided by Williams’ work, researchers were able to recover seasonal changes in body and environmental chemistry from millions of years ago.

Green, Smith and Williams have worked for the past five years to refine and apply these techniques to living and fossil humans. In 2018, their work yielded the first accurate assessment of ancient seasonality from the teeth of Neanderthal children. The team is currently planning to sample fossil African hominin teeth from the Turkana Basin.

This article was written by Janaina Ávila of Griffith University. Susan Cote of the University of Calgary; Wendy Dirks of Durham University; and Dawn Lee and Christopher Poulsen of the University of Michigan, Ann Arbor. This research was funded by Harvard, Columbia and Griffith universities.

Adapted from Griffith University press release.

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