Late Miocene hominids from the Middle Awash, Ethiopia

 

Summary of article appearing in Nature, Volume 412 July 12, 2001, pages 178-181
Article by Yahannes Haile-Selassie.

Additional information from the article:
Geology and paleontology of the Late Miocene Middle Awash valley, Afar rift, Ethiopia
By: Giday Wolde Gabriel, Yohannes Haile-Selassie, Paul R. Renne, William K. Hart, Stanley H. Ambrose, Berhane Asfaw, Grant Heiken and Tim White
In: Nature, Volume 412, 12 July 2001, Pages 175-178.

 

Eleven hominin (early human) fossils, dated to between 5.2-5.8 Ma, were found in the Middle Awash Valley of Ethiopia. These fossils may hold information about the earliest humans since they come from the time between 7 and 5 million years ago when the chimpanzee and human lineages are thought to have split. The fossils have been placed in a new subspecies, Ardipithecus ramidus kadabba. At least five individuals are represented by the fossil remains.

The specimens have a mixture of primitive features shared with other apes and derived characteristics that are unique to hominins. One of the features characteristic of all later hominins is the shape of the canine tooth, which looks more like an incisor than the ape canine does. This group of fossils is also linked to later hominins by the presence of features of a toe bone (phalanx) that are consistent with moving bipedally on the ground.

The authors believe that the features shared with later hominins unite this species with hominins rather than with chimpanzees. Features that are primitive, as well as the date assigned to these fossils, suggest that this group is close to the last common ancestor of chimpanzees and humans. The subspecies name chosen for this group, kadabba, means “basal family ancestor” in the Afar language.

Scientists are also interested in discovering what kind of environment the early hominins inhabited. The environmental settings were determined using geological and chemical information, and by the types of fossil animals found in the fossil localities. Geologists found that the sediments of these sites had originally been deposited in lakes or rivers, indicating a wet environment. Also, chemical analysis of carbonates showed that the carbon isotope ratios were low, indicating the presence of woodland or grassy woodland habitats. The vertebrate fossils found with the hominins are remains of animals whose modern relatives live in wet areas and forests. An example of this is the cane rat, Thryonomys, which today is found around rivers and lakes. Other animals, such as reduncine bovids, indicate that there may have also been more open woodlands close to the lake.

This paleoenvironmental evidence shows that these early hominins were associated primarily with wooded and wet environments. The scarcity of hominin fossils from other localities that are less wooded suggests that the early hominins might not have frequented open areas until after 4.4 million years ago.

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