193
CHAPTER SEVEN
Skeletal System
SKELETAL CLUES TO THE PAST
tures that have preserved human ancestors from more than 6 million years ago
to recent times.
It took an international team three years to assemble the human skulls
from Herto and another three to analyze them suF
ciently to publish preliminary
results. The researchers compared the skull dimensions to 6,000 modern human
skulls.
H. sapiens idaltu
had facial features much like ours and a slightly larger
and longer head. It will be interesting to learn more about these ancestors.
A
s a hard and enduring human tissue, bone provides impor-
tant clues to the distant past. We have a glimpse of our
ancestors from 156,000 years ago in skulls discovered near
the town of Herto in Ethiopia. Driving by Herto after a sea-
son of punishing rains, paleoanthropologist Tim White of
the University of California, Berkeley, spotted a skull jutting from the sand
near the Awash River. The skull, from a hippo, bore cut marks indicating
butchery. Returning with helpers, the researchers uncovered the fossilized
remains of three human skulls, preserved because the rain had driven the
modern-day residents and their cattle from Herto before they could trample
the evidence.
The researchers named this earliest known member of the human fam-
ily
Homo sapiens idaltu,
which means “elder” in the local Afar language. One
adult skull was that of a young man and because it was only partially crushed,
could be reconstructed; another was damaged beyond recognition. The
third skull was that of a child about seven years old. It had been smashed into
more than 200 pieces and scattered over a 400-square-meter area. Telltale
clues suggested reverence for the dead: The skulls were smooth, as if they
had been repeatedly handled, and they bore highly symmetrical cut marks.
They were also found alone, with no other body parts, suggesting that they
had been transported. Some societies treat skulls in this manner to honor
the dead. Nearby were many stone blades, axes, and ±
aking tools. It looked
like a band of early humans had lived near a shallow lake that formed when
the river over±
owed. Other preserved bones indicate that the lake was also
home to hippos, cat²
sh, and crocodiles, and that bu³
alo lived near the sur-
rounding lush vegetation. This part of Ethiopia has unusual geological fea-
´ossilized skulls from 156,000 years ago provide glimpses of the oldest known
anatomically modern humans,
Homo sapiens idaltu
.
7.1
INTRODUCTION
A bone may appear to be inert because of nonliving material
in the extracellular matrix of bone tissue. However, bone also
includes active, living tissues: bone tissue, cartilage, dense
connective tissue, blood, and nervous tissue. Bones are not
only alive, but also multifunctional. Bones, the organs of the
skeletal system,
support and protect softer tissues, provide
points of attachment for muscles, house blood-producing
cells, and store inorganic salts.
PRACTICE
1
List the living tissues in bone.
7.2
BONE STRUCTURE
The bones of the skeletal system vary greatly in size and
shape. However, bones are similar in structure, develop-
ment, and function.
Bone Classif
cation
Bones are classiF ed according to their shapes—long, short,
at, or irregular
(f
g. 7.1)
.
Long bones
have long longitudinal axes and expanded
ends. Examples of long bones are the forearm and thigh
bones.
Short bones
are cubelike, with roughly equal lengths
and widths. The bones of the wrists and ankles are this
type.
Flat bones
are platelike structures with broad surfaces,
such as the ribs, scapulae, and some bones of the skull.
Irregular bones
have a variety of shapes and are usu-
ally connected to several other bones. Irregular bones
include the vertebrae that comprise the backbone and
many facial bones.
In addition to these four groups of bones, some authori-
ties recognize a F
fth group called
sesamoid bones,
or
round
bones
(see F g. 7.45
c
). These bones are usually small and
nodular and are embedded in tendons adjacent to joints,
where the tendons are compressed. The kneecap (patella) is
a sesamoid bone.
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