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Miami geologists part of Science magazine announcement: Oldest hominid skeleton unveiled

10/01/2009

Map showing the portion of Middle Awash area of the Afar Rift in Ethiopia where Ardipithicus ramidus fossils were uncovered.
photo: W. K. Hart, Miami University
Miami University geologists Bill Hart and Brian Currie are part of the scientific team that has uncovered new evidence for human evolution in the Afar Rift, Ethiopia. The unveiling of the oldest hominid skeleton yet reported took place Oct. 1 in Ethiopia's capital city Addis Ababa.

New results of a 17-year investigation of the 4.4. million-year-old hominid Ardipithecus ramidus appear in the Oct. 2 special issue of the journal Science.

These results open a new chapter on human evolution by extending knowledge into a previously poorly known period, only a few million years after the human line diverged from that leading to chimpanzees.

The findings reveal the kind of human ancestor that came before the better-known “ape-man” Australopithecus, until now the most completely known early hominid genus thanks to fossils like the skeleton of “Lucy” discovered in Ethiopia in 1974. The new fossils reveal the early evolutionary steps that our ancestors took after we diverged from our common ancestor with chimpanzees.

The centerpiece discovery is a 4.4 million-year-old partial skeleton of a female nicknamed “Ardi.” The team recovered important parts of the skeleton including the skull with teeth, arms, hands, pelvis, legs and feet.
This is now the earliest skeleton known from the human branch of the primate family tree. That branch constitutes the zoological family “Hominidae”; Hominids include Homo sapiens as well as all species closer to humans than to chimpanzees and bonobos, humans’ closest living relatives.

Hart, chair and professor of geology, and Currie, associate professor of geology at Miami, are co-authors of “The Geological, Isotopic, Botanical, Invertebrate, and Lower Vertebrate Surroundings of Ardipithecus ramidus,” one of the 11 papers that comprise the special issue of Science. A total of 47 scientists representing 10 countries and many different research areas of paleontology and geology worked together to author the 11 scientific papers.

Laboratory research conducted at Miami was instrumental in producing a detailed chemical profile of the major constituents of the glass shards found in volcanic ashes sandwiching the fossils. This unique chemical “fingerprint” allowed the Ardipithecus-bearing layer to be tracked across a 9-kilometer arc of exposure, providing an unparalleled transect across an ancient landscape.

The new fossils were found in the Middle Awash study area in Ethiopia’s Afar Rift, about 140 air miles (230 km) northeast of Addis Ababa. The Middle Awash study area preserves the longest, most continuous record of human evolution anywhere on earth. Here, about 300 hominid specimens are known from 14 separate superimposed stratigraphic horizons sampling the last six million years.

Hart was part of the team that identified the remains of the first Homo sapiens (published in Nature, 2003), and he and Currie were among scientists who recovered and identified fossils of the earliest species of the genus Australopithicus anamensis (published in Nature, 2006).

Related Media

Photos Photos  
Exposure of the Ardipithecus ramidus -bearing sediments above a prominent light colored, resistant horizon extending across the middle of the photo. This horizon is one of the volcanic ash layers used to establish the 4.4 million year age for the fossils. Erosional “badlands” topography characteristic of the research area can be seen in the background.
photo: W.K. Hart, 1994
other media SCIENCE_ARDI_MA_Backgr.circ.pdf

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