Image: FRED SPOOR; copyright National Museums of Kenya

Researchers working in Kenya have unearthed fossils that could upset a long-held view of human origins. According to a report published today in the journal Nature, the remains represent a previously unknown hominid genus and species from which modern humans may have descended. For decades that distinction belonged to Australopithecus afarensis¿a species typified by the famous 3.2-million-year-old Lucy skeleton. But the new discovery, dubbed Kenyanthropus platyops, comes from roughly the same time interval and thus renders Lucy's ancestral status far less certain.

Meave Leakey of the National Museums of Kenya and her colleagues recovered the Kenyanthropus remains¿which include jaws, teeth and a skull dated to between 3.2 and 3.5 million years old¿from mudstone sediments in northern Kenya¿s Turkana basin. (The skull is apparently the oldest almost complete early human cranium known.) Subsequent analysis revealed a creature rather different from Lucy and her kin. In particular, Kenyanthropus has a far flatter face and smaller molar teeth¿feeding-related differences that suggest the two groups could have coexisted without competing for food resources.

"Now that we have a new form of early hominid from the same time period that is quite distinct from afarensis, the anthropologists will have to decide which of these forms of early human actually lies in our ancestral tree," University of Utah geologist Frank Brown, who dated the fossil, remarks. "It cannot be both."