Miami University

Hart involved in hominid discoveries

A Miami geologist is part of the research team that has found a new species of human ancestor in east Africa and determined our ancestors used tools for butchering animals 2.5 million years ago.

William K. Hart (geology) and former graduate student Tonja Larson were working at the Ethiopia site in fall 1996, when the initial discoveries were made.
They traced and sampled numerous volcanic ash horizons near the hominid finds, focusing on a particular ash below the hominid-bearing sediments. Field preparation of the ash yielded many grains of the mineral feldspar, later used at the Berkeley Geochronology Center to determine its 2.5 million year age. Additional chemical analysis of this and other nearby volcanic layers continues at Miami and the Los Alamos National Laboratory.

“It’s a key time because the genus Homo evolved from Australopithe-cenes. There’s been poor fossil evidence for when it happened, and this may bring us to a closer time period,” says Hart.

“The new species is most like its ancestor afarensis (e.g. Lucy),” said White. “The face projects forward, the braincase is crested and small, but the premolars and molars are enormous. This combination of features has never been seen before.”

The discoveries, made between 1996 and last December, come from the Bouri peninsula in the Middle Awash study area in the Afar desert of Ethiopia. The new fossils were dated by the argon-argon radioisotopic method.

In 1994, the same research team announced the discovery of Ardipi-thecus, the earliest known hominid at 4.4 million years old, at the nearby Middle Awash site of Aramis.

The new discoveries are important for three reasons.
• They add a new potential ancestor to the human family tree.
• They show the thigh bone (femur) had elongated by 2.5 million years ago, a million years before the forearm shortened, to create our familiar human proportions.
• Evidence shows the earliest stone technologies were aimed at getting meat and marrow from large mammals. This signals a dietary revolution that may have eventually paved the way toward an invasion of new habitats and continents.
The scientists can’t tell whether this species used stone tools, but the proximity of cutmarked bones provides circumstantial support for this idea.
Scientists say more fossils will be needed to reveal whether human evolution between 2 million-3 million years ago was “jerky” or relatively smooth.
Hart plans to return to Ethiopia this fall with fellow researchers to seek more details in the dating and environment of these hominids. He has visited Ethiopia in 1983, 1984, 1990, 1994 and 1996.

Hart conducts research in igneous petrology, volcanology and isotope geochemistry and maintains field programs in Alaska, Ethiopia and the northwestern United States.

His Ethiopian research since 1990 has been funded in part by the National Science Foundation and the Ohio Board of Regents.

Date Published: 04/29/1999
Volume: 18   Number: 34