Australopithecus deyiremeda was a
contemporary of ‘Lucy’
Hominin
remains comprising a complete lower jawbone, a partial lower jawbone and two
partial upper jawbones, together with some accompanying teeth have been
described as a new species, Australopithecus
deyiremeda. The fossils were excavated in 2011 in the Woranso–Mille study
area, central Afar, Ethiopia. They were found in deposits dated from 3.3 to 3.5
million years old, making Australopithecus
deyiremeda a contemporary of Australopithecus
afarensis (the species to which the well-known fossil ‘Lucy’ belongs) and
the controversial hominin species Kenyanthropus
platyops. The specific name deyiremeda
means ‘close relative’ in the local Afar language and follows a now-established
tradition of using local languages to name hominin species.
Australopithecus deyiremeda is distinguished from Ardipithecus ramidus by its thicker
dental enamel and more robust lower jawbone. It is distinguished from Australopithecus afarensis by a number
of features of its lower jawbone, by the positioning of its cheekbones in
relation to the upper jawbone, and by its smaller back teeth.
What
are the implications of this discovery? For a long time, it was believed that
there was just the one hominin species, Australopithecus
afarensis, living in the period from four to three million years ago, in
East Africa. It was possible to argue that the earlier Australopithecus anamensis (4.2 to 3.9 million years ago) and the
later Australopithecus garhi (2.5 million
years ago) were simply early and late forms of the same species and that Australopithecus bahrelghazali from Chad
(known from a single 3.5-million-year-old specimen) represented a Central
African extension of its range. On this view, Australopithecus afarensis was a single, long-lived, geographically
widespread species, capable of occupying a wide range of habitats. Not until
2.8 million years ago did other hominin species start to appear: Australopithecus africanus and later Australopithecus sediba in South Africa
and the so-called robust australopithecines (Paranthropus) in both South Africa and East Africa.
Even
if Kenyanthropus platyops is
rejected, this view is no longer tenable. There is now incontrovertible evidence
that multiple australopithecine species were living in East Africa during the
Middle Pliocene. It is also notable that Australopithecus
afarensis has been recorded at Hadar, only 35 km (20 miles) north of Woranso–Mille.
Not only did these species overlap in time, they were close in geographical terms,
probably occupying differing feeding niches.
Early hominin evolution has been described as
more of a tangled bush than a family tree. In addition to Australopithecus afarensis, Australopithecus
deyiremeda and possibly Kenyanthropus
platyops, it is likely that the Ardipithecus
line was still in existence at this time. The Woranso–Mille site has also
yielded a 3.4-million-year-old partial hominin foot with an opposable big toe.
Though it has not been assigned to a particular species, the toe suggests Ardipithecus or something very similar.
With
the LD-50-1 lower jawbone pushing back the origins of Homo to 2.8 million years ago, later australopithecines such as Australopithecus sediba have been
bumped from the list of possible human ancestors. However, the Woranso–Mille
discovery means that we are no nearer identifying from just which part of the ‘tangled
bush’ the first humans emerged.
References:
1. Haile-Selassie, Y. et al., New species
from Ethiopia further expands Middle Pliocene hominin diversity. Nature 521, 483-488 (2015).
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