Kenyanthropus platyops: The Flat-Faced Man of Lake Turkana

Kenyanthropus platyops is a hominin species named in 2001 from a 3.5-million-year-old cranium found west of Lake Turkana in northern Kenya. Its name means “flat-faced man of Kenya”. Living at the same time as Lucy’s species, Australopithecus afarensis, it suggested that the human family tree was already branching widely more than 3 million years ago, a claim that remains debated.

Background: one species or many?

By the late 1990s many researchers thought that between about 3.9 and 3 million years ago only one hominin species lived in East Africa: Australopithecus afarensis, known from Lucy and the Laetoli footprints. Later periods, by contrast, clearly had several hominin species living side by side.

The area around Lake Turkana had already produced many important fossils, including the Turkana Boy skeleton of Homo erectus. The Kenyan palaeontologist Meave Leakey, working with the National Museums of Kenya, led fieldwork on the lake’s western side in the 1990s.

Discovery at Lomekwi

In August 1999 Justus Erus, a member of Leakey’s team, found a cranium at a site called Lomekwi, in sediments of the Nachukui Formation. Catalogued as KNM-WT 40000, the skull was nearly complete but broken into many pieces and filled with cracks into which rock had grown.

On 22 March 2001 Leakey, Fred Spoor and colleagues described the cranium in Nature as a new genus and species, Kenyanthropus platyops. A partial upper jaw from the same area, KNM-WT 38350, was included as part of the species. Volcanic ash layers dated by the argon method place the cranium at about 3.5 million years old.

Features of the skull

The skull had a small brain, comparable in size to that of australopithecines. What stood out was the face: the area beneath the nose was flat and vertical, rather than jutting forward as in Australopithecus afarensis. The cheekbones were tall and set forward, and the molar teeth were small.

This combination of a flat face and small molars resembled a much younger skull from the eastern side of Lake Turkana, KNM-ER 1470, about 1.9 million years old and usually assigned to Homo rudolfensis. Leakey’s team suggested that the two might be related and even proposed the name Kenyanthropus rudolfensis for the later skull, an idea that most researchers have not adopted.

The distortion debate

In 2003 the American palaeoanthropologist Tim White argued in Science that KNM-WT 40000 had been so heavily distorted by expanding rock in its cracks that its shape could not be relied upon. In his view, the flat face might be partly an artefact, and the skull could fall within the variation of Australopithecus afarensis.

Spoor and colleagues responded that key features, such as small molars, were not affected by distortion. In later years, virtual reconstructions using CT scans have been used to test the shape of the face, but specialists remain divided. Without more fossils, the question cannot be resolved.

Hominin diversity and the Lomekwi tools

The case for several species living around 3.5 million years ago has since been strengthened by other finds. These include Australopithecus deyiremeda, named in 2015 from jaws found at Woranso-Mille in Ethiopia, and the Burtele foot, a 3.4-million-year-old partial foot with a grasping big toe described in 2012.

In 2011 archaeologists working near Lomekwi found stone tools about 3.3 million years old at a site called Lomekwi 3. Published by Sonia Harmand and colleagues in 2015, they are older than the Oldowan tools of Olduvai. Kenyanthropus lived in the same region and is one possible toolmaker, but there is no direct evidence linking it to the tools.

Key people

• Meave Leakey, palaeontologist with the National Museums of Kenya and later the Turkana Basin Institute, who led the expedition and the naming of the species. She had earlier named Australopithecus anamensis in 1995.
• Fred Spoor, Dutch palaeoanthropologist and co-author, who specialised in using CT scanning to study fossil skulls.
• Justus Erus, the Kenyan field team member who found the cranium.
• Tim White, American palaeoanthropologist at the University of California, Berkeley, the most prominent critic of the new genus.

The discovery also illustrates the essential role of Kenyan fossil hunters, many of them from communities around Lake Turkana, whose sharp eyes have located a large share of the region’s most important hominin fossils over the past half century.

Timeline

• 1999, August: Justus Erus finds the cranium KNM-WT 40000 at Lomekwi.
• 2001, 22 March: Meave Leakey and colleagues name Kenyanthropus platyops in Nature.
• 2003: Tim White argues that the skull’s shape reflects distortion.
• 2011: Stone tools about 3.3 million years old are found at Lomekwi 3.
• 2015: The Lomekwi 3 tools and the species Australopithecus deyiremeda are published.

Why it matters

Kenyanthropus platyops challenged the idea of a single, simple line of ancestors between 4 and 3 million years ago. Whether it proves to be a separate genus or a distorted skull of a known species, it pushed scientists to take seriously the possibility that several kinds of hominin shared the landscapes of eastern Africa, and that human evolution was a branching bush rather than a ladder.