Elephant ancestors’ teeth evolved in response to long term changes in diet and climate in Africa

The University of Helsinki’s latest study on proboscideans (elephants and their ancient relatives) provides evidence that some proboscideans began adapting to grass-rich environments in East Africa by changing their behavior and consuming more grasses. This adaptation occurred in certain lineages of proboscideans, such as choerolophodonts, much earlier than previously believed, around 23 to 11 million years ago in specific regions of East Africa.

Around 7 million years ago in the lake Turkana region, the earliest true elephants started to have increasingly grass-rich diets in dryer and more grass-rich savanna environments compared to other parts of East Africa.

“This supports the hypothesis that certain regions acted as ‘species-factories’, where evolutionary adaptation to changing environmental conditions first occurred,” says Juha Saarinen, the lead researcher from the University of Helsinki, whose study was published in Nature.

Feeding on grasses is more challenging on teeth compared to other types of plants due to the high content of phytoliths, mineral grains, in grass leaves, causing significant wear on the teeth.

However, during the Early and Middle Miocene, the choerolophodont lineage of proboscideans managed to shift to more grass-rich diets with relatively minor changes in their tooth structure.

Since approximately 10 million years ago, major climate changes have had a substantial impact on the evolution of proboscidean teeth in East Africa, particularly in the development of highly specialized high-crowned, multi-ridged molar teeth in true elephants (Elephantidae).

“We discovered that the peak periods of drying in East African climate over the past 7 million years, such as around 4 and 2 million years ago, coincided with significant evolutionary bursts in tooth crown height and the number of ridges on molar teeth. These evolutionary changes did not reverse during periods of less severe climatic conditions,” explains Saarinen.

“This supports previous suggestions that adaptive traits in organisms are responses to extreme rather than average environmental conditions.”

Comparing evidence of past vegetation and the diet of elephants over the past 7 million years revealed an increase in grasslands and the dominance of grass-feeding elephants with highly specialized teeth throughout most parts of East Africa during that period.

However, during the past 100,000 years, this situation changed, likely due to significant fluctuations in global climate. Eventually, only the dietarily more versatile modern African savanna elephant (Loxodonta africana) with less specialized teeth survived in East Africa. Similarly, the Asian elephant (Elephas maximus) was able to survive in Asia due to its ecological versatility, while the African forest elephant (L. cyclotis) found refuge in more forested parts of Central and Western Africa.

“The environmentally adaptable modern elephants were the sole survivors of the turbulent climate changes of the late Pleistocene. Now, it is us humans who pose a threat to the survival of these ecologically vital animals, and we must make every effort to prevent their extinction,” emphasizes Saarinen.

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