Exciting new fossils discovered east of Lake Turkana in Kenya confirm that there were two additional species of our genus – Homo – living alongside our direct human ancestral species, Homo erectus, about 2 million years ago.
The finds, described in the journal Nature, include a face, a remarkably complete lower jaw, and part of a second lower jaw uncovered between 2007 and 2009 by scientists of the Koobi Fora Research Project (KFRP). A critical contribution to the interpretation of the new finds was the preparation of 3D virtual reconstructions using sophisticated computer technology.
About 40 years ago, the KFRP’s scientists discovered the enigmatic fossil known as KNM-ER 1470 (or ’1470′ for short). This skull, readily distinguished by its large brain size and long flat face, ignited a longstanding debate about just how many different species of early Homo lived alongside Homo erectus during the Pleistocene epoch. 1470’s unusual morphology was attributed by some scientists to sexual differences and natural degrees of variation within a single species, whereas others interpreted the fossil as evidence of a separate species.
This decades-old dilemma has endured for two reasons. First, comparisons with other fossils have been limited due to the fact that 1470’s remains do not include its teeth or lower jaw. Second, no other fossil skull has mirrored 1470’s flat and long face, leaving in doubt just how representative these characteristics are. The new finds address both issues.
“For the past 40 years we have looked long and hard in the vast expanse of sediments around Lake Turkana for fossils that confirm the unique features of 1470’s face and show us what its teeth and lower jaw would have looked like,” said Dr Meave Leakey, co-leader of the KFRP. “At last we have some answers.”
“Combined, the three new fossils give a much clearer picture of what 1470 looked like,” added co-author Dr Fred Spoor of the University College London’s Department of Cell and Developmental Biology. “As a result, it is now clear that two species of early Homo lived alongside Homo erectus. The new fossils will greatly help in unraveling how our branch of human evolution first emerged and flourished almost two million years ago.”
Found within a radius of just over 10 km from 1470’s location, the three new fossils are dated between 1.78 million and 1.95 million years old.
The face KNM-ER 62000, discovered in 2008, is very similar to that of 1470, showing that the latter is not a single ‘odd one out’ individual. Moreover, the face’s well-preserved upper jaw has almost all of its cheek teeth still in place, which for the first time makes it possible to infer the type of lower jaw that would have fitted 1470.
A particularly good match can be found in the other two new fossils, the lower jaw KNM-ER 60000, found in 2009, and part of another lower jaw, KNM-ER 62003, found in 2007.
KNM-ER 60000 stands out as the most complete lower jaw of an early member of the genus Homo yet discovered.
Bibliographic information: Leakey et al. 2012. New fossils from Koobi Fora in northern Kenya confirm taxonomic diversity in early Homo. Nature 488, 201–204; doi: 10.1038/nature11322