Leakey and colleagues believe this shows that Kenyanthropus had a much different diet than Lucy's species. The different physical features show both were likely adapted to different environments, which would have prevented competition for food, says Spoor. The two could even have lived side by side, he says.
Of all other known hominids, Kenyanthropus bears a striking resemblance to another unusual skull found by Richard Leakey, Meave's husband, in the 1970s. That hominid, named Homo rudolfensis, dates to a much later period of about 2 million years ago.
Rudolfensis has long puzzled scientists and has been moved between two different hominid groups — Homo and Australopithecus — because researchers were never really sure where to put it, says Spoor. The Nature article proposes that rudolfensis could be descended from Kenyanthropus.
The topic likely to occupy evolutionary biologists for some time is Leakey's assignment of a new genus Kenyanthropus, which effectively creates two main trunks to the human family tree.
But Daniel Lieberman, an evolutionary anthropologist at George Washington University, says the new genus, for the time being, is the most comfortable classification of the new skull.
"None of the other possible solutions seem feasible," he said in a Nature article commenting on the Leakey find. "My guess is that it will be quite a while before we can confidently determine the position of Kenyanthropus platyops in the human evolutionary tree."