New hominin genus from eastern Africa shows diverse middle Pliocene lineages.

Summary of article appearing in Nature Vol 410; 22 March 2001, 433-440

Article by Meave G. Leakey, Fred Spoor, Frank H. Brown, Patrick N. Gathogo, Christopher Kiarie, Louise N. Leakey, & Ian McDougall

This article announces a new genus and species of early human, Kenyanthropus platyops, which is based on fossilized bone remains found at the Lomekwi localities in the Turkana District of northern Kenya. Discovered by an international team led by Meave Leakey, the new finds shed new light on human evolution in the middle Pliocene. Prior to the announcement of Kenyanthropus platyops, the known fossils suggested that only one species of early human had existed in East Africa between 3.5 and 3 million years ago. The new finds instead support the idea that multiple species of early hominin had evolved during this time span.

The fossils were found west of Lake Turkana, Kenya, and were preserved in floodplain deposits. The discoveries include a largely complete cranium (the skull minus the lower jaw), a temporal bone (one of the bones that form the side and base of the cranium), two partial maxillae (paired bones that fuse together to form the upper jaw), and isolated teeth. The cranium is the holotype for the species, meaning it is the specimen on which the original description of the species is based. The maxillae is also considered to be a member of the newly named species, making it the paratype, a specimen also important to the original description and included in the initial publication.

Analysis of these two specimens shows a marked difference from two previously known genera of early humans older than three million years -- Ardipithecus and Australopithecus. Although the overall size of the Kenyanthropus cranium is within the range of two previously known species of Australopithecus (A. africanus and A. afarensis), the authors state that size alone is not an adequate clue to classification. Instead, they identify features of the Kenyanthropus lower face that are unique, including the projection of the lower face, the shape and positioning of the facial bones, and tooth morphology. This evidence combined with a collection of primitive features (such as a small ear canal and the lack of an occipital/marginal sinus system) warrants naming of the new genus Kenyanthropus.

There are several implications of this discovery. First, identification of a previously unknown lineage indicates that the period of human evolution between 3 and 4 million years ago may have included a diversity of species - much like later periods. Before this discovery, only one species -- named Australopithecus afarensis -- was known to have roamed East Africa during this time span. Since multiple species coexisted throughout most of human evolutionary history, many paleoanthropologists felt it only a matter of time before a second (or third) species would be found and dated to this early stage in human evolution. Kenyanthropus is that new branch in the family tree (see the human phylogenetic tree for a diagram).

The second implication concerns taxonomy and ancestry. Despite a separation of 1.5 million year, Kenyanthropus platyops shares a remarkably similar facial architecture to a later species known as Homo rudolfensis. This observation challenges the taxonomic status of the latter species: Does it really belong to the genus Homo, or to the new genus Kenyanthropus? Another implication is that researchers must now reassess fragmentary fossils found from this time period to look for affinities to the new genus.

Besides a description of the new material, the article gives other information about the site, including the paleoenvironment and fauna of the area. The Lomekwi area was a floodplain of the ancestral Omo River at the time when Kenyanthropus lived there. This suggests that these hominins lived in a lake margin environment. The faunal assemblage collected from the site supports this environmental interpretation. The different species that inhabited the area show that the area was well watered and vegetated. Scientists expect that this kind of information will eventually help reconstruct how Kenyanthropus platyops lived and how its way of life may have differed from that of other species of early humans.

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