Justus Erus, a Kenyan research assistant working on a team led by Meave Leakey, discovered the KNM-WT 40000 skull in 1999. The mostly complete cranium was found in two pieces, with the braincase separated from the face. The small brain and ear canal are similar to those of the very earliest humans like Austraolpithecus anamensis or even modern chipanzees. Conversely, its flat face, high cheekbones, and small, thickly-enameled teeth are traits found in later human fossils like those of Homo rudolfensis or Homo habilis from around 2 million years ago.
The flat-faced skull is considered the holotype for Kenyanthropus platyops; however, there is controversy around its identification. KNM-WT 40000 is considerably distorted, which leads some paleoanthropologists to believe that the skull actually belongs to an Au. afarensis individual. Since KNM-WT 40000 is the only known Kenyanthropus individual, this makes features for the entire species hard to pinpoint. Until scientists find more fossils belonging to Kenyanthropus platyops, both the species identification and the sex of KNM-WT 40000 remain unresolved.