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Elements of the axial skeleton recovered from the Hadar formation 1974Ц1977 collections.

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 57531-635 11982)
Elements of the Axial Skeleton Recovered From the Hadar
Formation: 1974-1 977 Collections
C. OWEN LOVEJOY, DONALD C. JOHANSON, AND W E S COPPENS
Departments of Anthropology and Bwlogy, Kent State University, Kent, Ohio 44242
fC.OL.1;Department of Orthopaedic Surgery, Case Western Reserve University,
Cleveland, Ohio 44106fC.OL.);Cleveland Museum of Natural History, Cleveland, Ohio
44106 fC.OL,D.C.J.);Znstitute of Human Origins, 2700 Bancroff Way, Berkeley,
California, 94704 (D.CJ.); Department of Human Anatomy, Northeast Ohio
Universities College of Medicine, Rootstown, Ohio 44272 fC.OL.1,and Laboratoire
d'Anthropologie, Musde de l'Homme, Paris 75016, France (Y.C.)
KEY WORDS
Hadar, Vertebrae, Ribs, Hominid, Australopithecus
ABSTRACT
Anatomical descriptions are presented for the rib and vertebral
elements recovered from the Hadar Formation during the 1974-1977 field seasons, inclusive.
The following are anatomical descriptions of
the elements of the axial skeleton recovered
by the International Afar Research Expedition
during the field seasons of 1974-1977, inclusive (Johanson et al., this volume). Anatomical
nomenclature follows general usage and Trotter and Peterson (1966). Mensuration is included appropriate to the completeness and
condition of each specimen. Metrics employed
are either those in general use or are specifically described. The vertebral specimens have
been given individual description. Rib specimens are presented without further comment
in Table 1. While extensive radiography and
computed automated tomography were performed on many of the specimens described
below, the density of the Hadar fossils makes
interpretation difficult and these results are
not included at this time. Morphometric, biomechanical, and kinematic studies are currently in progress and results will be reported
subsequently. Vertebral and rib elements of
the A.L. 288-1 partial skeleton are described
in Johanson et al. (this volume).
DESCRIPTIONS
A.L. 333-51: Thoracic Vertebra (no figure)
The specimen is an adult centrum from a
midthoracic vertebra. It is in excellent preservation, although the arch was truncated
from the body cleanly a t its base. Both superior
and inferior surfaces bear demifacets, so it may
be restricted in number between two and nine.
0002-948318215704-0631$02.00G 1982 ALAN R. LISS. INC.
The superior surface is heart-shaped, with the
anterior portion distinctly triangular. The
more compact cortical bone formed by the
adhesion and fusion of the ring apophysis is
unusually broad, with a n average transverse
dimension of 6.8 mm. The inferior surface appears more typical of modern human vertebrae, although its surface is less clearly interpreted because of adhering matrix that cannot
be safely removed. Both the superior and inferior demifacets are quite large. There appears to be very mild osteophytosis in its earliest stage of development. The specimen is
probably from a young adult.
The vertical thickness of the centrum taken
anteriorly is 16.8 mm. Taken posteriorly it is
18.4 mm. The transverse breadth of the superior surface is 24.8 mm, and that of the inferior is 31.4 mm. The anteroposterior length
along the midline of the superior surface is
20.8 mm; that of the inferior 21.8 mm.
A.L. 333-73: Lumbar Vertebra (Fig. 1D,F)
The specimen is a lumbar vertebral body
with no associated arch. The base of the right
pedicle is preserved. The entire surface of the
specimen has been badly abraded, but it has
retained its original shape. Only the lateral
and posterior surfaces of the body have original
surface intact. All other areas of the specimen
have lost a thin layer of surface bone, although
this has had only minimal metrical affect. The
inferior central rim is broken away on the right
Received March 17, 1981; accepted December 10,1981.
632
LOVEJOY, JOHANSON, AND COPPENS
TABLE I . Costal skeleton metrics frnm.)
Suecimen
A.L. 333-118
333w-17
333w-18
333w-19
333w-30
333~-41
333w-44
333w-45
333w-47
Portion
Dreserved
Side
Head
Proximal
Proximal
Middle
Distal
Left
Head
Middle
Right
Robable
number
Maximum
dimension
S1
height
AP
breadth
SI height
Costochondr. jct.
ML breadth
Costochondr. jct.
1
1-3
2-3
31.0
25.0
42.5
65.0
63.7
11.2
12.2
7.5
8.3
15.7
10.9
24.4
52.8
11.9
5.9
3-10
3
A.L. 333-83: Altas (Fig. lG,H)
The specimen is a fragment from the left side
of an atlas vertebra. It includes the superior
and inferior articular surfaces and a portion
of the posterior arch. The superior articular pit
is well preserved although there are two fossilization cracks near its anterior extremity.
These have been naturally retained in perfect
apposition. The groove for the vertebral artery
just posterior to the pit is well preserved and
is deep and broad. The transverse process has
been truncated cleanly from the articular process a t both points of attachment. A portion of
the posterior arch is preserved but is truncated
before midline. The area in which the tubercles
for the transverse ligament should be represented has suffered mild damage, which has
obscured observation of this feature. The articular pits are deep medially and high latA.L. 333-81: Immature Thoracic Centrum
erally, resulting in a very steep articular wall,
(Fig. 1 A B )
considerably steeper than in modern human
The specimen is the body of an immature specimens.
The maximum overall dimension is 34.0
thoracic vertebra. This assignation is based on
the condition of the superior and inferior sur- mm. The inferior facet has a breadth of 11.3
faces of the centrum, which indicate no fusion and a length of 16.1 mm. The superior facet
of the ring apophyses. The arch has been trun- has a breadth of 10.8mm.
cated from the body through the right pedicle
A.L. 333-101: Axis Vertebra (no &we)
and the left lamina, removing approximately
one-third of the articular facet on the left side.
The specimen is a complete axis vertebra.
The specimen has a very small body, but bears Unfortunately, it is so badly abraded that esboth upper and lower demifacets, so it is prob- sentially no surface was left intact, such that
ably either a second or third thoracic. The su- only the outline core of the specimen is preperior surface is gently convex, whereas the served. No further description is warranted at
inferior surface is moderately concave. There this time.
is a central vascular pit in the posterior side
A.L. 333-106: Cervical Vertebra (Fig.1CJ)
of the centrum for the basivertebral vein.
The specimen is an essentially complete
The anterior height (superoinferior) of the
specimen is 11.8mm; posteriorly it is 12.0mm. lower cervical vertebra. The specimen is adult
The anteroposterior centrum diameter supe- and in excellent condition. Both transverse
processes have suffered breakage of their distal
riorly is 14.2mm; inferiorly it is 15.5 mm.
side and is composed of three major apposed
fragments on the left. There has been slight
distortion as a consequence of imperfect apposition. A sufficient amount of pedicle base
is preserved on the left side to indicate that no
rib facet was present (hence the lumbar status
of the specimen). The most notable features of
the specimen are the great height of the body
(relative to its other dimensions), and general
size. The ring apophyses are fused and the
specimen is fully adult.
The superoinferior height of the centrum
taken anteriorly is 25.0 mm; taken posteriorly
it is 24.5 mm. The mediolateral breadth of the
inferior surface is 37 .Omm; the anteroposterior
length, 24.1 mm. The same measures for the
superior surface are 34.0 and 22.7 mm, respectively.
HADAR AXIAL SKELETON
tips; the spinous process has a minor fossilization crack a t its base of no consequence. The
right lamina is traversed by a small crack; the
left pedicle is also traversed by a small crack
with slight bone loss. Otherwise the specimen
is essentially complete and undistorted.
The foramina1 area for the basivertebral
vein is bifid and bisected by a large bony ridge
running superoinferiorly. The foramina for the
vertebral arteries are both single and are of
approximately equal size. The spinous process
is not bifid. The vertebral foramen is large and
ovoid, showing relative anteroposterior elongation. The centrum is unusually small relative to the remainder of the specimen. The superior articular surface of the body is typically
concave, with marked angulation of the posterolateral lips. The anterior and posterior tubercles of the transverse process are thin and
ridge-like, and in general quite gracile. The
superior surface of the costotransverse bar
bears a deep mediolateral groove (between the
anterior and posterior processes). The spinous
process is very long, and shows almost no angulation with respect to the plane of the inferior central surface. It is probably a C-6 or
c-7.
The superior centrum breadth (mediolateral) is 20.5 mm. The length of the spinous
process from posterior tip to the vertebral
canal is 28.2 mm. The maximum transverse
breadth along an axis over both articular facets is 42.5 mm. The internal transverse and
anterosuperior dimensions of the spinal canal
are 18.0 and 12.6 mm, respectively.
A.L. 333w-8:Vertebral Fragment (no figure)
The specimen is a fragment of an adult vertebral body. Only the anterior one-third is preserved. Both superior and inferior surfaces are
badly eroded. The anterior surface is coated
with matrix that cannot be safely removed. No
significant morphology is preserved.
A.L. 333w-14:Vertebral Spine (no figure)
The specimen is the spine of an adult cervical
vertebra. No portion of the remainder of the
neural arch is preserved. Its apex is not bifid.
Its base is large and triangular, and the specimen as a whole is considerably robust.
A.L. 333x-12:Thoracic Vertebra (Fig. 2)
This is a complete midthoracic or lower thoracic vertebra. While the specimen has good
surface morphology and is virtually complete,
it has suffered considerable distortion of a
cryptic type (mostly as the result of plastic de-
633
formation). This distortion lies in the juncture
between the body and neural arch. The most
direct way of viewing this change is in lateral
view. In this view the inferior vertebral notch
can be seen to be unusually V-shaped and not
U-shaped. This condition has resulted from
some downward compression and superiorward shear of the pedicles, i.e., the specimen
has been anteroposteriorly shortened and the
neural arch moved superiorly in this process.
The external aspects of both pedicles display
bony evidence of this process. On the right side
there is a prominent ridge of extruded bone
along the lateral aspect of the pedicle near the
shear crack. On the left, the area is dissected
and slightly fragmented. While the body is otherwise undistorted, the neural arch bears several large and many minor fossilization cracks.
A large matrix-filled crack traverses the left
lamina from the superior articular facet to the
inferior articular facet, resulting in some expansion. On the right side, the midpoint of the
transverse process is traversed by a crack,
which is matrix-filled. The process appears
otherwise undisturbed at first glance, but the
cryptic nature of the distortion of this specimen
is brought out well in this location. The right
transverse process is considerably shorter than
the left, and its terminal process expanded,
with marked rotation of the rib facet. A second
fossilization crack runs longitudinally along
its centroidal axis. The plastic deformation and
crushing of the specimen have produced these
changes, which at first sight appear only as
minor defects because of the compaction of the
bone. The distal half of the spinous process has
been fractured and rejoined with some posterior deviation of the distal segment. The laminae are traversed by numerous fossilization
cracks of no great consequence, although the
bone surface has been largely disrupted by this
process. In general, in addition t o the changes
described for the transverse process on the
right side, the entire neural arch has been
translated superiorly and anteriorly, which
has also altered the angle of the rib facets and
the spinous process. The latter should be more
angulated to the plane of the centrum, and the
rib facets should face more laterally. The inferior vertebral notch should be more U-shaped
and more open than is presently the case.
The specimen is subadult. There is no evidence of any ring fusion and the characteristic
subapophyseal morphology of the centrum surface is evident. The tip of the spinous process
does not bear a fused epiphysis. The specimen
is probably a T-7, T-8,or T-9; it is most likely
Fig. 1. A, A.L. 333-81, inferior; B, A.L. 333-81, superior; C, A.L. 333-106, inferior; D, A.L. 333-73, inferior; E, A.L. 333106, 333-106. superior, F,A.L. 333-73, superior; G, A.L. 333-83, superior; H, A.L. 333-83, inferior.
635
HADAR AXIAL SKELETON
a T-7. There is a very large expanded crack
through the inferior articular facet. The right
superior facet has had its superior tip broken
away. The articular facets are otherwise in
good condition* Save for cracks that have no
metric significance. There has been abrasion
of several areas of the lateral walls of the body.
Once corrected for distortion, the specimen
bears a remarkable similarity to modern human vertebrae.
LITERATURE CITED
Trotter. M, and Peterson, R (1966) Osteology. In ELJ Anson
(ed): Morris' Human Anatomy. New York: Saunders, pp,
133-315.
A
B
Fig. 2. A, A.L. 333X-12, posterior (specimen inverted); B, A.L. 333X-12, inferior.
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