Two New Species Of Humans: Recent Fossils From The Turkana Basin Shed Light On Early Human Evolution

 Photo credit: Fred Spoor.

Exciting new fossils discovered east of Lake Turkana confirm that there were two additional species of our genus –Homo – living alongside our direct human ancestral species, Homo erectus, almost two million years ago. The finds, announced in the scientific journal Nature on August 9th, include a face, a remarkably complete lower jaw, and part of a second lower jaw. They were uncovered between 2007 and 2009 by the Koobi Fora Research Project (KFRP), led by Meave and Louise Leakey (both of Stony Brook University and the Turkana Basin Institute). KFRP’s fieldwork was facilitated by TBI and supported by the National Geographic Societ.

 

This is a nearly complete lower jaw with a full set of teeth. Its characteristic small front teeth (incisors) and flat profile across the incisors is consistent with the shape of the newly published specimen KNM-ER 62000 and skull KNM-ER 1470.

This mandible was spotted by Cyprian Nyete, who was clambering over a very steep hillside, in his search for fossils. Looking up he spotted a fragment of a fossil close to the top of the slope. The rest of this specimen had washed down a small gully and had been covered with silt and rocks. All the missing pieces were slowly recovered by screening all the surface rocks and sands and excavating areas where it seemed possible more of the fossil might be buried under the surface. There was just a slim chance, with such a complete lower jaw preserved, the skull of this individual might have been nearby. But this did not turn up.

 

Four decades ago, the KFRP 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 earlyHomo 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.

 

A 3D reconstruction of mandible KNM-ER 60000 from CT scan data. 

Credit: Fred Spoor.

Meave (L) and Louise Leakey, discussing one of the new fossils at the time of discovery. 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.

 Photo credit: Mike Hettwer.

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 fossils 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,” says Meave Leakey. “At last we have some answers.”

“Combined, the three new fossils give a much clearer picture of what 1470 looked like,” says Fred Spoor, leader of the scientific analyses. “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.”

Credit: Fred Spoor

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 by field crew member Elgite Lokorimudang 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 by Cyprian Nyete in 2009, and part of another lower jaw, KNM-ER 62003, found by Robert Moru in 2007. KNM-ER 60000 stands out as the most complete lower jaw of an early member of the genus Homo yet discovered.

The team working on the new finds included Christopher Kiarie (TBI), who carried out the laboratory preparation of the fossils, Craig Feibel (Rutgers University), who studied the age of the fossils, and Susan Antón (New York University), Christopher Dean (UCL, University College London), Meave and Louise Leakey (TBI, Kenya; and Stony Brook University, New York) and Fred Spoor (Max Planck Institute for Evolutionary Anthropology, Leipzig and UCL), who analysed the fossils. The National Geographic Society funded the fieldwork, the Leakey Foundation funded geological studies, and the Max Planck Society supported laboratory work.

View the new fossils in 3D

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