Fossilized cheek teeth have helped paleontologists learn a lot about what ancient elephants ate millions of years ago. Turns out, those with a less picky diet and more adaptability to changing environments survived. And those who stuck to a grass-based diet went extinct when there were extreme fluctuations in the climate.
“This supports the hypothesis of such regions as 'species-factories' where evolutionary adaptation to changing environmental conditions first centered around," said Juha Saarinen, a paleontologist at the University of Helsinki and lead author, in a statement. Details on the study were published in Nature Ecology & Evolution.
Chewing grass is more demanding on teeth than feeding on other types of plants because of its high content of mineral grains called phytoliths in the leaves. These minerals cause heavy abrasion on pearly whites.
Still, early proboscideans in the Early and Middle Miocene belonging to the choerolophodon lineage, shifted to more grass-rich diets, causing a changing appearance in their teeth.
About 10 million years ago, changing climates across East Africa had a great effect on the evolution of proboscidean teeth. True elephants (Elephantidae) especially, had changes like high-crowned, multi-ridged molar teeth.
“We were able to show that the strongest peaks of drying of the East African climate during the last 7 million years (for example about 4 and 2 million years ago) correspond with evolutionary bursts in the increase of tooth crown height and the number of ridges on the molar teeth,” said Saarinen.
Teeth Evolve in Extreme Environments
The find supports earlier suggestions that teeth traits adapt to extreme environmental conditions rather than normal or average conditions.
When comparing past evidence of vegetation and the diets of elephants from seven million years ago, scientists found an increase of grasslands and grass-feeding elephants with specialized teeth designed to grind down grasses. However, this changed in the last 100,000 years because of fluctuations in the global climate during the late Pleistocene. During this time, alternating humid and arid climatic cycles were more rhythmic and in greater magnitude than earlier in this time period.
Eventually, only the modern African savanna elephant (Loxodonta africana) with less specialized teeth and a more versatile diet survived.
Elephants of Today
A modern elephants’ ability to thrive in various environments and versatility to eat multiple types of food might also explain the Asian elephants (Elephas maxius) survival in Asia, and the African forest elephant’s (Loxodonta cyclotis) capability of finding a habitat in more forested areas of Central and Western Africa.
The comparison of dental fossils of various species and the structures found on the teeth explained this adaptation. The research included the number of enamel loops, enamel thickness and enamel folding. All these traits are considered adaptations for resisting abrasion.
“The ecologically quite versatile modern elephants were the sole survivors of the tumultuous climate changes of the late Pleistocene. Now it’s us humans that threaten the last surviving species of this ecologically important group of animals, and we should work hard to keep them from being lost forever,” said Saarinen.