One-Million-Year-Old Cranium of Genus Homo Found in Eritrea

Summary of article appearing in Nature Vol. 393; 04 June 1998

Article by Ernesto Abbate, Andrea Albianelli, Augusto Azzarolli, Marco Benvenuti, Berharne Tesfamariam, Piero Bruni, Nicola Cipriani, Ronald J. Clarkes, Giovanni Ficcarelli, Roberto Macchiarelli, Giovanni Napoleone, Mauro Papini, Lorenzo Rook, Mario Sagri, Tewelde Medhin Tecle, Danilo Torre, Igor Villa

In excavations conducted between 1995 and 1997 in Eritrea (East Africa on the Red Sea), a team of paleoanthropologists found several early human fossils in layers dating to roughly one million years before present. The excavation was conducted in a 500m thick portion of a formation known as the Danakil Formation. The fossils found include one nearly complete cranium (UA 31) of genus Homo, two pelvic fragments (UA 173), and two permanent lower incisors (UA 222 and UA 369). The four finds were separate, and the research team does not associate the fossils with one individual.

It was not possible to radiometrically date the layers around where the cranium was found using the Potassium-40 method, due to natural contamination of the crystals. However, the team was able to reconstruct the biostratigraphy (the animal fossils found in the same formation have been dated elsewhere to occur during the early and early middle Pleistocene -- 1.7 million to 10,000 years ago) and magnetostratigraphy (97 samples of the sediments were taken across the 500m of the formation to discover four distinct zones: two "normal" magnetic zones -- where magnetic north is toward the North Pole -- and two "reversed" magnetic zones -- where magnetic north is toward the South Pole). From these pieces of information, the team was able to find the correct sequence of reversed and normal magnetic field during the correct time period, based on the animals found in the deposits. From the position of the cranium, a date of roughly one million years before present was assigned.

The cranium is a nearly complete brain case with most of the basicranium (bottom of the skull) missing. Parts of the facial bones and the maxilla (upper jaw) were recovered, although no tooth crowns remain. Several roots of teeth are preserved, molars and premolars, and the presence of the third molar on the right side indicated a young adult age, at the least, for this individual at time of death.

The cranium is still encased in silty sediments, and cleaning and preparation for formal study are taking some time. Preliminary study of the cranium exhibits some modern Homo features in conjunction with many features typical of Homo ergaster. The estimated cranial capacity is between 750 and 800cc, and the cranium is long and ovoid in shape. There is a large supraorbital torus (browridge), the skull exhibits prognathism below the nose (the face projects forward of the brain) and the greatest width of the skull is at the base of the brain case. However, when viewed from the front, there is no evidence of a sagittal keel (protrusion running the length of the skull along the midline). A sagittal keel is not to be confused with a sagittal crest: see photographs of KNM WT 17000 for an example of a sagittal crest, and the Weidenreich reconstruction of Homo erectus for an example of a sagittal keel. Additionally, the greatest width between the parietal bones is placed highly, creating a more vaulted (modern) shape to the brain case.

The research team has declined to place the specimen in a species at the moment pending a full comparative study, due to the mixture of modern traits with traits typical of Homo ergaster, the presence of which at such an early date increases the variation of the Homo population considerably.

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