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Article history:
Received 24 April 2007
Accepted 15 May 2008
Keywords:
Anatomically modern Homo sapiens
Omo Kibish
Middle Stone Age
the associated postcranial elements recovered during that expedi-
tion. No morphological description of the postcrania was provided
at that time, other than the observation that they appeared to be
anatomically modern. In 1991, Day and colleagues published a more
over the age and provenance of the Kibish hominids and to
gather more information about the archaeological and faunal
context of the Kibish material. Using photographs and maps
from the 1967 Leakey-led expedition, the KHS locality was
relocated and verified. Extensive surface collections, new ex-
cavations, and microstratigraphic studies (see Feibel, 2008)
were conducted at the site. New specimens attributed to the
Omo I skeleton were discovered at KHS, including a fragment
of right femur that conjoins with the distal femur discovered in
* Corresponding author.
E-mail addresses: ompear@unm.edu (O.M. Pearson), danielle.royer@sunysb.edu
Contents lists availab
Journal of Hum
.el
Journal of Human Evolution 55 (2008) 421–437(D.F. Royer), frederick.grine@sunysb.edu (F.E. Grine), john.fleagle@sunysb.edu (J.G.Introduction
The initial discovery of the Omo I hominin skeleton was made in
1967 by a Kenyan team, led by Richard Leakey, of the International
Palaeontological Research Expedition to the Omo Valley, south-
western Ethiopia (Leakey, 1969; Butzer, 1969; Butzer and Thurber,
1969; Day, 1969). The specimens came from near the top of
Member I of the Kibish Formation, at the KHS (Kamoya’s Hominid
Site) locality. The Omo I remains were first described by Day (1969),
who provided a preliminary description of the cranium and listed
thorough anatomical description focused on the Omo I postcranial
remains, along with limited metric analyses and comparisons.
While the cranial remains of Omo I (and Omo II) have continued to
figure prominently in debates on modern human origins, the Omo I
postcranial material has rarely been incorporated into comparative
studies.
In 1999, 2001, 2002, and 2003, an international team of
researchers returned to the Omo Valley to renew excavations in
the Kibish Formation. The goal of this effort, the Kibish Pa-
leoanthropological Project, was to resolve longstanding debatesFleagle).
0047-2484/$ – see front matter  2008 Elsevier Ltd.
doi:10.1016/j.jhevol.2008.05.018Recent fieldwork in the Kibish Formation has expanded our knowledge of the geological, archaeological,
and faunal context of the Omo I skeleton, the earliest known anatomically modern human. In the course
of this fieldwork, several additional fragments of the skeleton were recovered: a middle manual phalanx,
a distal manual phalanx, a right talus, a large and a small fragment of the left os coxae, a portion of the
distal diaphysis of the right femur that conjoins with the distal epiphysis recovered in 1967, and a costal
fragment. Some researchers have described the original postcranial fragments of Omo I as anatomically
modern but have noted that a variety of aspects of the specimen’s morphology depart from the usual
anatomy of many recent populations. Reanalysis confirms this conclusion. Some of the unusual features
in Omo Ida medially facing radial tuberosity, a laterally flaring facet on the talus for the lateral malleolus,
and reduced dorsovolar curvature of the base of metacarpal Idare shared with Neandertals, some early
modern humans from Skhul and Qafzeh, and some individuals from the European Gravettian, raising the
possibility that Eurasian early modern humans inherited these features from an African predecessor
rather than Neandertals. The fragment of the os coxae does not unambiguously diagnose Omo I’s sex: the
greater sciatic notch is intermediate in form, the acetabulum is large (male?), and a preauricular sulcus is
present (female?). The preserved portion of the left humerus suggests that Omo I was quite tall, perhaps
178–182 cm, but the first metatarsal suggests a shorter stature of 162–173 cm. The morphology of the
auricular surface of the os coxae suggests a young adult age.
 2008 Elsevier Ltd. All rights reserved.article info abstractA description of the Omo I postcranial s
newly discovered fossils
Osbjorn M. Pearson
a,
*
, Danielle F. Royer
b
, Frederic
a
Department of Anthropology, MSC 01-1040, University of New Mexico, Albuquerque, N
b
Interdepartmental Doctoral Program in Anthropological Sciences, Stony Brook Univers
c
Department of Anatomical Sciences, Stony Brook University, Stony Brook, NY 11794, U
d
Department of Anthropology, Stony Brook University, Stony Brook, NY 11794, USA
journal homepage: wwwAll rights reserved.leton, including
. Grine
c,d
, John G. Fleagle
c
7131, USA
tony Brook, NY 11794, USA
le at ScienceDirect
an Evolution
sevier.com/locate/jhevol1967 (see Fig. 7).

From geological studies conducted during the recent expedi-
tions, McDougall et al. (2005; see also Brown and Fuller, 2008;
McDougall et al., 2008) were able to establish a more secure age
framework for the Omo I fossils. Using
40
Ar/
39
Ar dating of feldspars
from tuffs in Members I and III of the Kibish Formation, they
demonstrated that the KHS fossils must be older than 1041 ka,
but younger than 196 2 ka. Additionally, geological correlations
to sapropel phases, the isotopic ages of pumice clasts in Member I,
and evidence of the rapid deposition of Member I further narrow
the age estimate to approximately 195 5 ka for the Omo I fossils.
Thus, the Omo I skeleton is currently the oldest well-dated ana-
tomically modern human fossil.
The main goal of this paper is to present the results of a com-
prehensive study of all postcranial specimens attributed to the Omo
I skeleton (Fig. 1), including details regarding the state of preser-
vation, morphological description, and illustration. Furthermore,
this paper provides a cross-referenced list of the various specimen
O.M. Pearson et al. / Journal of Huma422Fig. 1. The Omo I partial skeleton. Arrows indicate the newly recovered specimens. An
outline of a Dinka man figured by Roberts and Bainbridge (1963) surrounds the bones.numbers that have been applied to the skeleton in the decades since
its initial discovery, noting instances of prior description, illustra-
tion, and analysis. In addition to the specimens that are described
here, there are approximately 125 bone fragments that remain
unidentified and that could not be refitted to another fragment. Day
et al. (1991: 596) briefly described these as ‘‘approximately 800
grams of unidentified bone fragments’’ (our translation).
Geological context
The Omo I skeleton was initially discovered by Kamoya Kimeu as
a surface find near the base of a small hill in extensively dissected
terrain on the east side of the Omo River. Following the collection of
material on the surface, a step trench was dug into the hill and it
was determined that the fossils had come from a single level in the
upper part of Member I of the Kibish Formation (Butzer, 1969; see
also Feibel, 2008). A laterally extensive excavation was made at this
level that resulted in the in situ recovery of a few faunal remains,
some stone tools, and a few skeletal elements of Omo I (Leakey,
1969; Clark, 1988). The additional parts of the skeleton that were
recovered in the recent fieldwork were all found on either the
deflated and eroded surface of the main excavation level from 1967
or on the eroded slopes within a few meters below that level. In
addition, paleontological collecting indicated that all of the mam-
malian fossils in the immediate vicinity of this hill appear to be
eroding from this same level.
As is evident from the following descriptions and illustrations,
the Omo I skeletal fossils preserve many parts of both the appen-
dicular and axial skeleton, but in a very fragmentary condition. Only
the left clavicle, the right talus, the right first metacarpal, and a few
other elements of the hand and foot are essentially complete. Most
elements are extensively fractured and broken, but only a few show
evidence of deformation or crushing, most notably the humeral
heads. Some elements, especially the distal femur, show evidence
of extensive postmortem abrasion. There are numerous pits and
scratches on various elements.
Although no taphonomic analysis has been conducted on the
Omo I fossils, all studies support the original interpretation that the
interment of fossils was the result of normal geological processes.
There is no evidence to support arguments that the presence of the
Omo I fossils in Member I of the Kibish Formation was the result of
an intrusive burial from a later time period (e.g., Klein, 1999).
Likewise, given that no skeletal element is duplicated and that all
appear to derive from an adult individual, the remains constituting
Omo I almost certainly derive from a single associated skeleton.
Morphological description: upper limbs
Elements of the upper limb are relatively well represented in the
Omo I individual. Most of the upper-limb specimens were collected
during the 1967 Leakey-led expedition, although three new finds (a
glenoid cavity fragment of the scapula, a manual middle phalanx,
and a manual distal phalanx) were made during the course of re-
cent fieldwork. The complete inventory of upper-limb remains is
provided in Table 1.
Pectoral girdle
The pectoral girdle of Omo I consists of a nearly complete left
clavicle, a fragment of the right clavicle, both scapular coracoid
processes, and a fragment of the glenoid cavity of the right scapula
(Fig. 2).
Specimen KHS 1-32 is a nearly complete left clavicle, lacking
only the medial and acromial ends (Fig. 2a; see also Voisin, 2008).
n Evolution 55 (2008) 421–437The clavicle displays some crushing of the inferior aspect of the
lateral end of the shaft, while the acromial end of the shaft is