The human family tree has a new member: a big-toothed early human ancestor that lived in Ethiopia 3.3 to 3.5 million years ago, according to a paper in the latest issue of the journal Nature.
The newly discovered human, named Australopithecus deyiremeda, overlapped in both time and region with yet another prehistoric human, "Lucy" (Austrolithecus afarensis). The find is strong evidence for the presence of more than one closely related early human ancestor species prior to 3 million years ago.
Because this particular species' teeth had super thick enamel and its jaws were built to last, "it probably engaged in heavy chewing and consumed harder, tougher, and more abrasive dietary resources," lead author Yohannes Haile-Selassie, curator of physical anthropology at The Cleveland Museum of Natural History, told Discovery News.
Photos: Faces of Our Ancestors
Haile-Selassie and his team analyzed the remains, which were collected from the central Afar region of Ethiopia. Combined results from three established different dating processes yielded the estimated age of the fossils.
The location where the fossils were found is just 21.8 miles south of where "Lucy" lived in Hadar, Ethiopia. The researchers think the species could have lived in even closer proximity. The two might have co-existed, which would be like Homo sapiens now sharing turf with another type of human.
While such a scenario today seems unfathomable for humans, it was likely common back in the day.
As for why, Haile-Selassie said, "There is some evidence that during the middle Pliocene time period (about 3.3 million years ago) when multiple hominins (early humans) were running around, there were rivers supporting gallery forests that laterally extend to woodlands and grasslands."
"It was an ecosystem that supported numerous and varied habitats," he continued. "With niche partitioning, a number of related taxa can co-exist in such an ecosystem."
Photos: What Did Prehistoric Humans Eat?
Anthropologists debate about which species is the stem of Homo sapiens, meaning that it should be positioned at the very bottom of the human family tree. Candidates now include two other early humans, Ardipithecus ramidus and Australopithecus anamensis, but it could also be an as-of-yet undiscovered species.
Whichever it was, the stem species, via evolution and divergence, could have later resulted in more than 20 different types of humans, including Homo sapiens.
In terms of what happened to this crowded field of early relatives, Haile-Selassie said, "Some of them gradually gave rise to a new form and went extinct. Others went extinct with no descendants."
He added, "When the environment changes and their habitat diminished, or when they faced harsh competition with others for resources and failed to be good competitors, they had no alternative but extinction."
The fossil evidence for the earliest anatomically modern humans comes from Ethiopia, so it cannot be ruled out that A. deyiremeda and/or "Lucy" is our direct ancestor.
Sophisticated Tool Kit Predates Humans
Other than what the tooth and location evidence might reveal about their diets and habitats, little is known about the culture of such early humans. Intriguingly, a collection of stone tools dating to 3.3 million years ago was recently found at a site called Lomekwi 3 in Kenya. For now, though, the maker of those relatively sophisticated tools–consisting of anvils, hammers and more–remains a mystery.
Yet another mystery is a 3.4-million-year-old partial foot found by Haile-Selassie and his colleagues in the same region of Ethiopia where A. deyiremeda was discovered. Could it have belonged to yet another different type of human?
That remains to be determined. What's clear, for now, is that East Africa was bustling with early human activity long before our species ever evolved.
"It is remarkable to have two closely related species that appear to have lived in the same area, during approximately the same time period," said Fred Spoor of both the Max Planck Institute for Evolutionary Anthropology and University College London, and author of a "News & Views" article in Nature about the find.
"This raises the important question whether and how they differed in their behavior, diet or other ways that made long-term co-existence possible."