New Discoveries From Ethiopia Fill Major Gap In Fossil Record (7/12/2007)

A complete lower jaw (mandible) of Australopithecus from a locality called Nefuraytu located in the Woranso-Mille study area. This specimen is one of the most complete jaws from sites older than 3.0 million years ago. Photo Credit: The Cleveland Museum of Natural History

Scientists working in the Woranso-Mille area of the Afar Region, Ethiopia, have recovered fossils that may prove to be a bridge to establishing a relationship between the earlier Australopithecus anamensis (4.2 - 3.9 million years) and the later Australopithecus afarensis (3 - 3.6 million years) early human species.

Researchers have hypothesized an ancestor-descendant relationship between these two species based on their similarities. However, until now, there has been no hominid fossil record from the 3.6 - 3.9 million years time frame to determine this relationship. According to project co-leader Dr. Yohannes Haile-Selassie, curator and head of physical anthropology at The Cleveland Museum of Natural History, his team’s 2007 field season in the Woranso-Mille study area was unusually successful and uncovered key physical evidence.

“We recovered fossil hominids that date to between 3.5 and 3.8 million years ago,” said Haile-Selassie. “These specimens sample the right time to look into the relationship between Australopithecus anamensis and Australopithecus afarensis and will play a major role in testing the ancestor-descendant hypothesis.” The project team found isolated teeth from this time frame during its earlier field seasons. However, during the 2007 field season, they recovered more complete jaws that are important to conduct comparative analysis.

At least 40 hominid specimens have been recovered thus far, including a number of complete jaws found in 2007, and a partial skeleton found in 2005. These join the more than 1,900 vertebrate fossil specimens discovered in four consecutive field seasons in the Woranso-Mille area. A total of more than 35 mammalian species in more than 20 genera have been sampled to date.

Introduction

The Afar Depression of Ethiopia has yielded early hominid fossil remains spanning the last 6 million years. This has placed Ethiopia in the forefront of paleoanthropology, the study of human physical and cultural evolution. Ethiopia is known to the world as the cradle of humankind, with a minimum of 12 early human species known from the country, including the earliest hominid Ardipithecus kadabba at 5.8 million years ago, and Homo sapiens idaltu, the earliest anatomically modern human at 160,000 years ago. For the last four decades, numerous local and foreign scientists have carried out fieldwork in the Afar region, searching for fossil remains of the earliest human ancestors. Major areas that have been extensively explored, and have yielded early hominid fossil remains include Hadar, Middle Awash, Gona, and Dikika, all located in the Afar Regional State. The Afar region still has unexplored areas of paleoanthropological interest. As a result, new exploratory programs are being developed and new paleontological sites identified.

The Woranso-Mille project, led by Drs. Yohannes Haile-Selassie and Bruce Latimer of The Cleveland Museum of Natural History, Cleveland, Ohio, United States, has been conducting its paleoanthropological research in the central Afar area since 2003. This area was identified as a result of survey and exploration conducted in 2002. The Woranso-Mille Project is a multinational and multidisciplinary project and has thus far conducted four consecutive field seasons within the Mille-Chifra-Kasagita Triangle. Members of the project include scientists from The Cleveland Museum of Natural History, the Addis Ababa University, Case Western Reserve University, and Berkeley Geochronology Center.

The Site

Yohannes Haile-Selassie, curator and head of physical anthropology at The Cleveland Museum of Natural History, working on newly discovered hominid fossils in the paleoanthropology laboratory at the National Museum of Ethiopia. - Photo Credit: The Cleveland Museum of Natural History

The Woranso-Mille paleontological site is located in the central Afar area in the Mille and Chifra districts of Zone 1 of the Afar Regional State. The study area is defined by the towns of Mille, Chifra, and Kasagita. In this study area, a total of 29 vertebrate localities have been designated thus far. Major fossiliferous areas are divided into propers, with a number of localities designated within each proper. The Aralee Issie, Mesgid Dora, and Makah Mera propers are located on the north side of the Mille River, and comprise a total of 11 designated localities. Additional localities on the north side of the Mille River are Godaya, Harabi, Am-Ado, and Lehaytu Gera. On the south side of the Mille River, major fossiliferous localities are designated in the areas locally known as Korsi Dora, Burtele, Nefuraytu, Leado Dodo'a, and Leadu.

The Fossil Discoveries

A total of 1,900 vertebrate fossil remains have been collected from the study area since 2003. Project leader Haile-Selassie states that these fossils represent diverse animals ranging from small mammals, such as mice, to large ones, such as elephants. Carnivores, monkeys, and bovids, are among the most abundant groups. However, other taxa, such as primitive horses, rhinoceros, hippopotamus, crocodile, and fish are also present. A total of more than 35 mammalian species in more than 20 genera have been sampled to date. The total number of fossil remains of early hominids discovered from the site is relatively small, as in other hominid-bearing sites in Ethiopia and elsewhere. However, at least 40 hominid specimens have been recovered thus far, including a number of complete jaws and one partial skeleton, which was found in 2005. The excavation of this partial skeleton is still under way.

Age of the Fossils

Significance of the hominid fossils

The fossil hominids from the Woranso-Mille area sample a time period that is poorly known in human evolutionary studies. An outstanding question in the study of early human evolution, says Haile-Selassie, relates to the relationship between the earlier Australopithecus anamensis (4.2 - 3.9 million years) and the later Australopithecus afarensis (3 - 3.6 million years). Researchers have hypothesized an ancestor-descendant relationship between these two species based on their similarities. However, there has been no fossil record from the 3.6 - 3.9 million years time frame thus far to test, confirm, or falsify this relationship. Haile-Selassie adds that the fossil hominids from the Woranso-Mille study area dated to between 3.5 and 3.8 million years ago sample the right time and play a major role in testing the hypothesis with fossil data. The Woranso-Mille fossil hominids from the deposits younger than 3.5 million years extend the geographic distribution of Australopithecus afarensis further to the north of Hadar, where the species is best documented.

Future Prospects

The paleontological significance of the Woranso-Mille study area has been demonstrated by the discovery of more than 1,900 vertebrate fossil specimens in three years of fieldwork. These fossils include a number of hominid remains from different time horizons. However, the study area has not been fully explored. Preliminary survey in some areas shows that there are fossiliferous deposits as old as 5 million years ago. However, the project has not yet intensively concentrated on these areas. During the coming field seasons, the Woranso-Mille project plans to systematically collect more fossils from already designated vertebrate localities and to find new areas with fossils of older age.

Note: This story has been adapted from a news release issued by The Cleveland Museum of Natural History

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