The oldest Homo fossil
The Great African Rift Valley (along which the continent is being sundered apart by convecting mantle currents or a mantle plume rising from below) was the cradle of the human family, and fossils of our distant ancestors have turned up along much of its length. Ethiopia is famed for hosting the oldest remains of our genus and its ancestors found so far, including the iconic Australopithecine Lucy. The recent discovery of a lower jawbone and five teeth eroding out of a rocky slope turned up some 15 km from the Lucy site, and was dated by several methods as the earliest piece of our genus found so far, at 2.8 million years old (some half million years older than the next in line).
Like Lucy and many other important hominid fossils, it was found in the Afar triangle, the triple junction point where the Nubian, Somalian and newly separated Arabian plates meet, and start drifting apart. Nowadays the area is desertic, but back in our ancestor's time it was open grass and shrub land with tree lined rivers, though the evidence suggests that the area was considerably wetter when the new find walked the Earth than in Lucy's day, some 200,000 years earlier. This may indicate a climatic transition that killed off Australopithecus and promoted the development of the larger brains of the hominids.
Fossil hominids are very rare, and few specimens that date from 2-3 million years back help us fill in some major gaps in the evolutionary line of our species, since the period remains poorly understood since evidence is very scarce. As a scientist put it, you can put the entire collection of our ancestors remains for the whole million years into a shoebox and still have room for the shoes. When Lucy's species died out, two main lineages developed out of it, one of which led to us but no record of the transition period had turned up until now.
The jawbone shares some 'primitive' features with Australopithecus like the shallow chin bone while also having distinctive hominid characteristics, such as thinner teeth, and represents the earliest transitional specimen, right at the beginning of our genus. The remains are too scanty to know whether they are the first known species on our lineage (Homo habilis) or another, so far undescribed species. The site is being explored for further remains, and we'll keep you posted if anything interesting turns up.
Loz
Image credit: Brian Villmoare/PA
http://news.nationalgeographic.com/news/2015/03/150304-homo-habilis-evolution-fossil-jaw-ethiopia-olduvai-gorge/ http://www.theguardian.com/science/2015/mar/04/jaw-bone-discovery-in-ethiopia-is-oldest-ever-human-lineage-remains