Fossils of Previously Unknown Early Human

Researchers in Ethiopia on Wednesday announced their discovery of fossils from a previously unknown member of the early human family, one that likely vied for survival in the same place and time as the iconic “Lucy” and her kin between 3.3 million and 3.5 million years ago.

Although the creature shares traits with other kinds of early humans, the researchers believe the thickly enameled teeth and fragmented jaw bones they found are evidence of an entirely separate species of hominin—the group that includes modern humans and our extinct predecessors. They’ve formally named the new species Australopithecus deyiremeda, which means “close relative” in the local language of the Afar region where they found it.

If confirmed by additional fossils, the discovery complicates what researchers long considered the only straightforward period of human evolution, stoking disputes over human origins. They reported their find in Nature.

“This discovery raises more questions than it answers,” said paleoanthropologist Brian Richmond at the American Museum of Natural History in New York, who wasn’t involved in the find. “The clear conclusion is that our early ancestors were more diverse than we appreciated.”

Not so long ago, Lucy’s species—Australopithecus afarensis—won global renown as the only human ancestor known in East Africa 3 million to 4 million years ago when the human family tree took root. More recently, though, fossil hunters have uncovered bones from perhaps three other small-brained, apelike hominin species alive at that same time, any one of which might have been directly ancestral to modern humankind.

“With the naming of this new species, the question of our evolution in that time period changes from whether or not there were multiple species to a matter of which one gave rise to later hominins,” and, ultimately to modern humanity, said Yohannes Haile-Selassie,curator of physical anthropology at the Cleveland Museum of Natural History, who led the research team. “If afarensis wasn’t the sole ancestor, then which one gave rise to which?”

Several experts, however, cautioned that the new specimen might belong to one of the hominin species already known from that era. In some ways, it resembles an afarensis hominin like Lucy; in others, it looks like another species from the same era called Kenyanthropus platyops discovered in Kenya in 1999, they said.

“I think they make a reasonable case for a new species, but it is a subtle situation,” said Fred Spoor, an expert in the evolution of human anatomy at University College London, who wasn’t involved in the project. “My strongest doubt is whether it is different enough.”

Paleoanthropologist Tim D. White, director of the Human Evolution Research Center at the University of California at Berkeley, worked on the original discovery of Lucy and of several other early hominin species. He dismissed the claim that the newer finds are evidence of a previously unknown human ancestor. They are well within the normal range of variation found in individuals belonging to the afarensis species, he said.

“Anatomical variation within a biological species is normal,” said Dr. White. “That’s why so many announcements of this sort are quickly overturned, and the newly proposed names become trivia questions on bad anthropology exams. Lucy’s species just got a few more new fossils.”

Write to Robert Lee Hotz at sciencejournal@wsj.com