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Miami faculty on team establishing 6 million year record of hominid evolution

Miami faculty are among scientists who have recovered and identified fossils in Ethiopia that help define the origin of the ape-man genus, Australopithecus. It is a find that represents the earliest species of the genus, Australopithecus anamensis, and that connects a 6 million year record of hominid fossils. The results of the discovery appear in the April 13 issue of the journal Nature.

Found in the Middle Awash valley of the Afar Region, Ethiopia, and dating to just over 4 million years old, the fossils represent unambiguous evidence for human evolution, say the researchers. William Hart (chair, geology) and Brian Currie (geology) were involved in the analysis and collection of supporting geologic information.

The new fossils are anatomically and chronologically sandwiched between the 4.4 Ma Ardipithicus ramidus and the 3.0-3.6 Ma Australopithecus afarensis (the “Lucy” species). This is the first time these three species have been shown to be time-successive in a single place, the Middle Awash study area.

Combined with other fossils recovered from the same region, this study confirms the longest, most-continuous record of human evolution on earth. A total of 246 hominid specimens from the Middle Awash region of Ethiopia are known from 12 separate superimposed stratigraphic horizons sampling the past 6 million years.

Hundreds of mammalian fossils were recovered at Asa Issie, one of the sites, and 30 hominid fossils, mostly teeth, were found, representing at least eight individuals. Faunal associations and sedimentological and geochemical data from the site suggest the hominids lived in closed woodland to grassy woodland ecological settings.

Fossils of Au. Anamensis were found from 1994-December 2005. The most recent discoveries, several teeth and a jaw fragment, were made at Asa Issie in December.

In 2003, Hart was part of the team that identified remains of the first Homo sapiens.

The Middle Awash research team, co-led by Tim White of U.C. Berkeley, includes more than 60 scientists from 17 different countries, specializing in geology, archaeology, paleontology and evolutionary biology. More than one-third of them co-authored this paper in Nature.

Support for this research comes from the National Science Foundation (including the Revealing Hominid Origins Initiative/HOMINID program), the Institute of Geophysics and Planetary Physics of the University of California at Los Alamos National Laboratory (LANL), the Japan Society for the Promotion of Science, the Fondation Singer-Polignac, and the Philip and Elaina Hampton Fund for Faculty International Initiatives.

How do they know it's that old?

This is where Hart and colleagues come in:

Led by Paul Renne at U.C. Berkeley, geologists used the single crystal, argon-argon (Ar/Ar) laser heating method to date a selected sample of the volcanic layer immediately below the fossil-containing beds at Asa Issie. The technique is a highly accurate method for determining the time that has elapsed since the eruption of a volcanic ash or lava flow. Combined with measurements on the magnetic polarity of the sediments, an age of 4.1 million years was determined.

At Alamos National Laboratories, chemical analysis was performed to determine the major constituents of the glass shards found in volcanic ashes overlying the fossils. The trace elements in this glass were measured by Hart at Miami, as a separate and confirming test. The combined results allowed the investigators to correlate these tuffs with samples of ash known from elsewhere in the Middle Awash and other fossil sites in eastern Africa.

Date Published: 04/13/2006
Volume: 25   Number: 32


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