Scientists are struggling to sort the relationships between their diverse collection of hominids (species of bipeds that are more closely related to humans than to apes).

Until fairly recently, there were only three known groups. Two of these, Homo (the genus from which modern man eventually evolved) and Paranthropus, were presumed to have descended from an early species in the third group, or genus, called Australopethicus; the most likely candidate being A. afarensis, the famous 3.2-million-year-old Lucy specimen unearthed in 1974.

But the picture has since been complicated, not least by the French discovery last year of a hominid now called Orrorin tugenensis.

This creature, which could represent an entirely new group of hominids, is claimed to be the oldest human-like creature known to science, taking the our lineage back to around six million years ago.

Scientific challenge

The flat-faced man unearthed by Leakey is also said to come from a completely new genus. Indeed, this new group may already have two members.

The features seen in Kenyanthropus platyops look very similar to those in a skull discovered by Meave Leakey's husband, Richard, on the eastern shore of Lake Turkana in the 1970s. That skull, formerly attributed to Homo rudolfensis, may now have to be reassigned.

Commenting on K. platyops, Daniel E. Lieberman, of the George Washington University, Washington DC, US, said the new creature would act "as a sort of party spoiler" as science attempted to determine its precise position in the human evolutionary tree.

He added: "A challenge for the next decade will be for skeletal biologists, palaeontologists and molecular biologists to work together, to devise new analytical methods with which to tease trustworthy signals from these data [information from skull and teeth fossils]."