Thursday, 28 May 2015

Yet another hominin species? The fossil evidence for human evolution grows even richer

Even more evidence for human evolution has been found in Ethiopia. Yohannes Haile-Selassie et al have announced in the latest edition of Nature the discovery of a hominin, Australopithecus deyiremeda dating between 3.3 to 3.5 million years ago:
Middle Pliocene hominin species diversity has been a subject of debate over the past two decades, particularly after the naming of Australopithecus bahrelghazali and Kenyanthropus platyops in addition to the well-known species Australopithecus afarensis. Further analyses continue to support the proposal that several hominin species co-existed during this time period. Here we recognize a new hominin species (Australopithecus deyiremeda sp. nov.) from 3.3–3.5-million-year-old deposits in the Woranso–Mille study area, central Afar, Ethiopia. The new species from Woranso–Mille shows that there were at least two contemporaneous hominin species living in the Afar region of Ethiopia between 3.3 and 3.5 million years ago, and further confirms early hominin taxonomic diversity in eastern Africa during the Middle Pliocene epoch. The morphology of Au. deyiremeda also reinforces concerns related to dentognathic (that is, jaws and teeth) homoplasy in Plio–Pleistocene hominins, and shows that some dentognathic features traditionally associated with Paranthropus and Homo appeared in the fossil record earlier than previously thought.
The question of whether this fossil is directly ancestral to us will of course be one of the first questions that laypeople will ask, and to be honest, that is secondary to the bigger question: - what does this tell us about hominin evolution in general. Irrespective of whether it is ancestral or not, or whether it deserves to be classified as a new species, or should be lumped in with an existing australopithecine, it provides yet more evidence for the diversity of hominin species. Once again, evolution is not a ladder, but a tree.

The left half of the lower jaw of Australopithecus deyiremeda. Image credit: Yohannes Haile-Selassie / Cleveland Museum of Natural History. (Source)

The type specimen (a-e) and paratype specimens (f-k) of Australopithecus deyiremeda. Image credit: Yohannes Haile-Selassie et al. (Source)

Casts of the jaws of Australopithecus deyiremeda. The specific name, deyiremeda, means ‘close relative’ in the language spoken by the Afar people. Image credit: Laura Dempsey / Cleveland Museum of Natural History. (Source)