Elephants thrived on early African grasslands

The excavation of the massive cranium of an early elephant species that roamed the grasslands on the northeastern side of Lake Turkana, Kenya, has helped scientists to understand why this species became the dominant elephant in eastern Africa. Loxodonta adaurora existed around the late Miocene to mid-Pliocene Epochs, and this particular skull is dated to around 4.5 million years ago. 

Known by its reference number, KNM-ER 63642, the specimen is from a large, adult male individual and is the most complete elephant cranium ever found from that time period.  It is about 85 percent intact and reveals a wealth of previously unknown anatomical detail, according to University of Michigan paleontologist William Sanders, who is also the study’s first author.

Loxodonta adaurora was one of seven or eight species of early elephants known from East Africa at that time and, although it was not a direct ancestor of modern African elephants, it was a closely related “cousin.”

At the time that L. adaurora roamed the landscape, the climate was cooler and drier; these conditions favored the spread of grasslands in this region. Many different animals, including horses, antelope, rhinos, pigs and hippos, were evolving simultaneously to graze grasses and were competing for the available forage. Loxodonta adaurora was among these grazers, and its impressive cranium shows several adaptations that would have made it successful at utilizing the grasses available at that time. 

Its cranium is unusual in being compressed from front to back, making the alignment of its chewing muscles well-suited for the efficient shearing of grasses. In addition, the elephant’s molars were higher-crowned and had thicker coatings of enamel and cementum than those of other early elephants. This would have made the teeth more resistant to the wear inherent in feeding on grasses close to the ground.

The study authors explained that the cranial morphology of KNM-ER 63642 is unexpectedly advanced for an elephant of its antiquity, and indicates that this species had already evolved craniodental adaptations to feeding on grasses by the early Pliocene Epoch. They hypothesize that these early adaptations helped make L. adaurora the dominant elephant species in the greater Turkana Basin at that time. 

“The adaptations of L. adaurora put it at a great advantage over more primitive elephants, in that it could probably use less energy to chew more food and live longer to have more offspring,” said Sanders, associate research scientist at the U-M Museum of Paleontology and in the Department of Anthropology.

The specimen was discovered in 2013 by a member of the Koobi Fora Research Project from a single molar that was visible at the surface. When it was excavated, it was found that the tooth was attached to an almost complete cranium lying upside-down under the surface of the substratum. It is estimated, from a previous excavation of another L. adaurora skeleton, that this individual was around 30 years old when it died, weighed about nine tons and probably stood about 12 feet at the shoulder, which is taller than average male elephants today.

“In my opinion, this elephant skull is by far the most impressive specimen that we have in the Kenyan paleontological collection from Lake Turkana, both in its completeness and in its size,” said paleontologist and study co-author Louise Leakey of the Koobi Fora Research Project. “When the teeth were seen on the surface, we had no idea that a complete cranium would be uncovered, and the excavation and recovery operation were both challenging and exciting.” 

Once the excavation was complete, the fossilized cranium, together with the plaster envelope that protected it on its journey, weighed about 2 tons. KNM-ER 63642 is now permanently housed at the Turkana Basin Institute’s facility in Ileret, Kenya. It is the only well-preserved elephant cranium from the interval beginning with the origin of elephants 8 million years ago and ending 3.5 million years ago, according to Sanders.

Elephants of this species most certainly coexisted with early hominins on the eastern African grasslands. In particular, fossil evidence of two australopithecine species has also been found from the region: Australopithecus anamensis fossils were recovered by Meave Leakey in and nearby the Lake Turkana Basin, Kenya, and fossil remains of A. afarensis were found at sites in Hadar, Ethiopia, and Laetoli, Tanzania.

Australopithecines would have benefitted from the presence of elephants in the early grassy woodlands and grasslands. Grazing by elephants would have helped keep the vegetation low and enabled our bipedal ancestors to look out for danger around them. Elephants also open access in the woodlands by knocking down trees and wearing pathways through the vegetation.  

“The origins and early successes of our own biological family are tied to elephants,” Sanders said. “Their presence on the landscape created more open conditions that favored the activities and adaptations of our first bipedal hominin ancestors.

“From this perspective, it is ironically tragic that current human activities of encroaching land use, poaching and human-driven climate change are now threatening the extinction of the mammal lineage that helped us to begin our own evolutionary journey,” he said.

The study is published in the journal Palaeovertebrata. 

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By Alison Bosman, Earth.com Staff Writer