When a cooler, drier climate allowed grasslands to spread and habitually bipedal human ancestors first appeared on the scene millions of years ago, a remarkably well-preserved fossil elephant cranium from Kenya is helping scientists figure out how its species became the dominant elephant in eastern Africa.

It is the only well-preserved elephant cranium from that time period, dating to 4.5 million years ago and unearthed at a site on the northeast shore of Lake Turkana. According to University of Michigan paleontologist William Sanders, it is around 85 percent complete and rich in previously unknown anatomical information.

KNM-ER 63642

The almost 2-ton skull belonged to a large adult male of the species Loxodonta adaurora, an ancient evolutionary relative of current African elephants but not a direct progenitor, and was known by its museum number, KNM-ER 63642.

KNM-ER 63642 is both massive and surprising contemporary in appearance, demonstrating modifications that most likely provided L. adaurora. According to Sanders, the main author of the research published online Oct. 21 in the journal Palaeovertebrata, he has an advantage when vying for grasses with other big animals. Meave and Louise Leakey, who supervised the recovery operation and are best recognized for finding early hominid remains and artifacts in Lake Turkana and elsewhere, are co-authors.

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L. Adaurora Skull

The L. adaurora skull is notable for being elevated and compressed from front to back, implying a new alignment of chewing muscles well-suited for effective grass shearing. Furthermore, the elephant's molars are higher-crowned and have thicker cementum coatings than those of other early elephants, making the teeth more resistant to wear prevalent in animals graze on grasses near the ground.

"The apparent synchronization of morphological adaptations and feeding behavior revealed by this study of Loxodonta adaurora may explain why it became the dominant elephant species of the early Pliocene," Sanders said. Sanders has spent nearly 40 years researching fossil elephants and their relatives in Africa and Arabia.

At the period, Eastern Africa had seven or eight recognized species of early elephants and horses, antelope, rhinos, pigs, and hippos. Many of these creatures had evolved into grazers, contending for the few remaining grasslands.

"The adaptations of L. adaurora put it at a great advantage over more primitive elephants in that it could probably chew more food with less energy and live longer to have more offspring," said Sanders, an associate research scientist at the University of Michigan Museum of Paleontology and in the Department of Anthropology.

Anthropological Study

Researchers and technicians from the Turkana Basin Institute, National Museums of Kenya, University of Michigan, Rutgers University, Smithsonian Institution, and the University of Utah collaborated on the elephant cranium's recovery, conservation, dating, description, and identification.

A Koobi Fora Research Project member identified KNM-ER 63642 in 2013 from a single molar visible at the surface.

Skull Condition

An almost intact skull was discovered during excavation. However, the tusks and jaws were not found, and no more remains from that person were found. At the time of death, the adult man was assessed to be between 30 and 34 years old.

The fossilized skull weighed around 2 tons, including the plaster coating that preserved it and some connected silt. Based on research into the bones of another L. adaurora mature male with a similar-sized cranium, this guy weighed almost 9 tons and stood around 12 feet tall at the shoulder, making him larger than modern-day male elephants.

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

The Turkana Basin Institute's facility at Ileret, Kenya, currently houses KNM-ER 63642 permanently. According to Sanders, it is the sole well-preserved elephant skull from the beginning, with elephant origins 8 million years ago and ending 3.5 million years ago.

The newly described cranium adds to our early elephant anatomy and our understanding of the connections between those creatures and our earliest human ancestors, the habitually bipedal australopithecines.

In eastern Africa, Loxodonta adaurora and other early elephants coexisted with two well-known australopithecine species: Australopithecusanamensis, discovered by Meave Leakey in and around the Lake Turkana Basin in Kenya, and Australopithecusanamensis, discovered by A. afarensis, which has been discovered in Ethiopia's Hadar and Tanzania's Laetoli.

As grassy woods and grasslands extended over eastern Africa, elephants in the early Pliocene would have helped the australopithecines. The animals' eating habits kept grasses low to the ground, allowing our upright forefathers to look above the plants and keep an eye out for predators.

Evolutionary Adaptation

Elephants can interrupt closed woods and create open regions by knocking over trees, uprooting plants, and trampling routes through dense forests. In addition, their feces contain nutrients and grass seed.

"Elephants are linked to our biological family's origins and early accomplishments," Sanders remarked. "Their presence on the terrain generated more open circumstances that supported our earliest bipedal hominid ancestors' activities and adaptations.

"From this standpoint, it is tragically terrible that present human actions such as increasing land usage, poaching, and human-caused climate change are now threatening the extinction of the animal lineage that assisted us in our evolution.

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