Friday, August 10, 2012

Fossils point to a big family for human ancestors

An upper skull found in 1972 and a newly discovered lower jaw are both thought to belong to the enigmatic hominin species Homo rudolfensis.

Fossilized skulls show that at least three distinct species belonging to the genus Homo existed between 1.7 million and 2 million years ago, settling a long-standing debate in palaeoanthropology.

A study published this week in Nature1 focuses on Homo rudolfensis, a hominin with a relatively flat face, which was first identified from a single large skull in 1972. Several other big-skulled fossils have been attributed to the species since then, but none has included both a face and a lower jaw. This has been problematic: in palaeoanthropology, faces and jaws function like fingerprints for identifying a specimen as a particular species (which is indicated by the second word in a Linnaean title, such as 'rudolfensis'), as opposed to the broader grouping of genus (the first word, as in'Homo').

Without complete skulls, it has been difficult to reach a consensus on whether specimens attributed to H. rudolfensis are genuinely members of a distinct species, or actually belong to other Homo species that lived around the same time, such as Homo habilis or Homo erectus. Understanding how many different Homo species there were, and whether they lived concurrently, would help to determine whether the history of the human lineage saw fierce competition between multiple hominins, or a steady succession from one species to another.

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