Written by
C. David Kreger
Introduction
The naming of a new species is almost always controversial, and Australopithecus
garhi is no exception. Named in the April 23, 1999, issue of Science,
the large research group that discovered the finds made some broad
claims and supposition that is definitely not accepted by all, though
any real acceptance of these claims and/or hypotheses will have to
come later on, as time enough passes for the information has been
fully disseminated, others have had a chance to examine the remains,
and the dust has settled.
The
remains that are directly attributed to the new species come from
the Hatayae Member of the Bouri Formation, Ethiopia, and have been
dated to approximately 2.5 myr. The type specimen of the species
is BOU-VP-12/130, an associated set of cranial fragments comprising
the frontal, parietals, and maxilla with dentition. The specimen
was discovered by Y. Haile-Selassie on November 20, 1997, and the
word garhi means "surprise" in the local Afar language.
These specimens are important no matter what the eventual final
attribution, due to the fact that the remains are from East Africa
at a time when there is very little remains (2.0-3.0 myr).
Diagnostic Features
One of the more striking features of the A. garhi remains
is the size of the postcanine dentition, which is at or beyond the
nonrobust australopithecine or A. robustus extremes. This
is the only feature that suggests any link to the robusts, and as
such it is very unlikely that the specimen is in any way derived
from or is a sister species to robustus. This is seen especially
in the large size of the anterior teeth, exceeding those of the
largest australopithecines and far exceeding the robusts, who are
marked by anterior tooth reduction or stasis. Based on tooth size,
the garhi material seems to fit well with schemes that see either
one or both of africanus and afarensis as a direct
human descendent, as the canine-to-premolar/molar size ratios are
comparable to both species and early Homo.
The
cranial attributes do not seem to directly make an attribution or
negate the possibility of attribution to a specific phylogeny, but
this may be due to the sparse nature of the remains and the small
sample size (the sample size must be kept in mind of any phylogenetic
discussion based on the described traits). Specific cranial attributes
include:
- The
lower face is prognathic with procumbent incisors.
- Canine
roots are placed quite laterally to the nasal aperture margin.
- The
premaxillary surface is separated from the nasal floor by a blunt
ridge and is transversely and sagittally convex.
- The
palate is vertically thin.
- The
zygomatic roots originate above P4/M1.
- The
dental arcade is U-shaped, with slightly divergent dental rows.
- The
temporal lines encroach deeply on the frontal, past the midsupraorbital
position and likely met anterior to bregma.
- The
postglabellar frontal squama is depressed in a frontal trigon.
The localized frontal sinus is limited to the medial one-third
of the supraorbital surface.
- There
is marked postorbital constriction.
- The
parietal bones have a well-formed, bipartite, anteriorly positioned
sagittal crest that divides above lambda.
- Cranial
capacity of approximately 450 cc (reconstructed).
Conclusions
There is not much to conclude at this point, merely to explain what
the researchers hypothesize as the possible phylogenetic relationship
of A. garhi. The researchers discuss the idea that garhi
represents a direct ancestor of modern humans that is derived from
africanus which is likely derived itself from afarensis. This does
fit in with Wolpoff's idea of an unidentified late africanus
group with many robust features, but know one can say with any certainty
at this point. The specimens may even be attributed to Homo
rather than Australopithecus. All that can be done now is
to watch what unfolds.
Bibliography
Aiello,
L., and C. Dean. 1990. An
Introduction to Human Evolutionary Anatomy. London: Academic
Press.
Asfaw,
B., T.D. White, O. Lovejoy, B. Latimer, S. Simpson, and G. Suwa.
1999. "Australopithecus garhi: A new species of early hominid
from Ethiopia." In Science, vol. 284, pp. 629-635.
Culotta,
E. 1999. "A new human ancestor?" In Science, vol. 284,
pp. 572-573.
de
Heinzelin, J., J.D. Clark, T.D. White, W. Hart, P. Renne, G. WoldeGabriel,
Y. Beyene, and E. Vrba. 1999. "Environment and behavior of
2.5-million-year-old Bouri Hominids." In Science, vol. 284,
pp. 625-629.
Wolpoff,
M. 1999. Paleoanthropology.
second edition. Boston: McGraw-Hill.
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