Fossils dating back 10 million years could redefine mammalian evolution

A set of fossil beds in central Türkiye is helping scientists reset the clocks on mammal evolution. Layers of volcanic ash mixed with bones have finally yielded precise ages, pinning the remains to between 7 million and 10 million years ago.

The ages come from argon-argon dating, a method that turns microscopic volcanic glass grains into miniature clocks and can measure time to a few hundred thousand years.

Academy Research Fellow Ferhat Kaya and colleagues at the University of Oulu led the international team behind the effort.

Argon-argon dating

For decades the best anyone could say about Central Anatolia’s fossils was that they were “late miocene.” Timelines depended on comparing the animals to relatives in distant European sites whose own ages were fuzzy.

Those comparisons created error bars of two to three million years, a headache when you are tracing gradual changes in teeth or limb bones.

Kaya’s group solved the problem by drilling through sandstone to sample pumice and lapilli deposited by ancient eruptions.

Each shard of volcanic glass trapped argon when it cooled. Using argon-argon dating, measuring the ratio of isotopes reveals how much time has passed since then.

The result is a set of five reference points that tighten the dating of dozens of fossil layers, according to the new study.

Why central anatolia matters

This rocky corridor sits between Africa, Asia, and Europe, so every change in climate or sea level created new migration routes.

Mammals that washed in from all three continents mingled here, leaving a unique record of faunal traffic.

Some of the most debated fossils belong to Ouranopithecus, a large ape that some researchers place near the common ancestor of African apes and humans.

Nailing down the age of these apes helps test whether they existed before, after, or alongside early hominines in Africa.

The updated timeline now brackets the Turkish Ouranopithecus site between 7.5 million and 8.2 million years.

That window overlaps with the 8.7 million year old Anadoluvius skull from nearby Çankırı, underscoring the region’s mix of hominine candidates.

Volcanic glass and argon-argon dating

Standard fossil beds rarely contain datable minerals because sedimentary rocks lack volcanic crystals. Central Anatolia is different, thanks to the cappadocia volcanic province that rained ash over river plains for millions of years.

Those ashes yield potassium rich feldspar that can be irradiated and measured with argon‑argon dating, shaving uncertainty down to about 0.3 million years, the USGS notes.

By pairing the dated ashes above and below each bone layer, the team could bracket each fossil horizon like a sandwich.

“While radioisotopic methods are not new in determining the age of fossils, this represents a significant paradigm shift in dating volcanic sedimentary layers that contain mammal fossils,” said Kaya.

In several cases, bones lay within two inches of datable tuff, providing nearly bulletproof ages. 

What the fossils reveal

The argon-argon dated layers hold more than 2,600 cataloged specimens, from three toed horses to saber toothed cats.

Shifts in species composition hint at a slow swing from wetter woodlands around 9.5 million years ago to open grasslands by 7.4 million years.

That ecological turnover matches global cooling events recorded in deep sea cores, tying local changes to planet wide climate swings.

Local fossils follow that global script; the mix of browsers and grazers shifts just when ocean records mark the late Miocene cooling.

Each dated horizon therefore becomes both a biological census and a climate gauge. Together they trace how rising plateau elevations and dropping temperatures nudged mammals toward new diets, behaviors, and territories.

Rethinking primate family trees

Pinning down an 8.7 million year age for Anadoluvius and similar dates for Ouranopithecus reopens the question of where hominines arose.

A 2023 study argued that the eastern Mediterranean apes could belong to the first radiation of the group that later gave rise to humans.

If Central Anatolia hosted early hominines while Africa was still home to their ancestors’ cousins, then migrations might have flowed southward, not northward. The new dating provides the temporal foothold to test that controversial scenario.

Kaya’s team expects to add hundreds of sites across the Central Anatolian Volcanic Province now that remote sensing guides them to ash filled gullies. Each new ash lens offers another clock to lock in the story of species moving and vanishing.

The same high precision approach can be applied wherever eruptions blanketed life, from the Andes to Java, rewriting evolutionary timelines one glass shard at a time.

The study is published in Proceedings of the National Academy of Sciences.

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