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 Scientists said on Wednesday the fossil represents the oldest
known representative of the human genus Homo and appears to be a
previously unknown species from the human lineage's earliest phases.
Our species, Homo sapiens, appeared only 200,000 years ago,
following a procession of others in the same genus. Until now, the
oldest known remains from the human genus were about 2.3 to 2.4
million years old and from the species Homo habilis.
"Although it is probably a new species, we are awaiting more
material before definitively naming a new species," said University
of Nevada, Las Vegas anthropologist Brian Villmoare, who helped lead
the research published in the journal Science.
The jawbone was found in 2013 in northeastern Ethiopia's Afar region
about 40 miles (64 km) from where the remains of "Lucy," one of the
most famous fossils of a human ancestor, were discovered in 1974.
Lucy's species, Australopithecus afarensis, immediately preceded the
Homo genus.
 The anatomy of the new fossil, encompassing the left side of the
lower jaw, suggests a close relationship with later Homo species. It
boasted features including tooth shape and jaw proportions that
separate early Homo lineage species from the more apelike
Australopithecus. But its sloping chin still has hints of Lucy.
"At 2.8 million years ago, this places the evolution of our genus
very close to 3.0 million years ago, which is when we last see
Lucy's species," Villmoare said.
The Homo genus, especially after 2 million years ago, developed
larger brains and tool use and began eating meat.
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The landscape where the individual belonging to the jawbone lived
probably had few trees except near water, like the modern Serengeti
Plains in Tanzania, with abundant grazing animals, hippos and
crocodiles, said Penn State University geoscientist Erin DiMaggio.
"If Homo was eating meat, it could have eaten any of the animals,
but we don't know much about that yet," added Arizona State
University anthropologist Kaye Reed. "It was a dangerous place.
Saber-toothed cats, hyenas and other large carnivores could have
preyed upon Homo."
A separate study in the journal Nature provided a fresh analysis of
a Homo habilis lower jaw from 1.8 million years ago, showing it was
unexpectedly primitive and resembled the much older newly discovered
jawbone.
(Reporting by Will Dunham; Editing by James Dalgleish)
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