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Skulls
are often associated with death, but like all bones, they are composed
of living tissue. Constantly changing, they grow larger, stronger
or weaker depending on age, diet and exercise. They can also heal
themselves when broken. Because of this, a skull is like a good
book - it can record the major events and traumas in an animal’s
life. Scientists read skulls to determine how long individuals
lived, how healthy they were, and how they died.
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Q: How
do bones grow?
RB: All bones have construction zones called growth plates, where
special bone-building cells work throughout an animal’s life. These
cells, called osteoblasts, use blood-borne tools like calcium and vitamin
D to construct and strengthen bone tissue.
Raymond
Bandar
Field Associate
Department of Ornithology & Mammalogy
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 SKULL
FACT
When they are born, male and female sea lions have very similar skulls.
However, once they are old enough to reproduce, the males develop a large
sagittal crest – a bony ridge where the jaw muscles attach to the
top of the skull. In sea lion colonies, only the dominant male mates with
the females. Males use strong jaw muscles to bite one another during competitions
for that opportunity.
SKULL
FACT
California sea lion skulls continue to grow in both length and width up
through about age ten. By age fifteen, all of the sutures, or seams between
the skull’s bony plates, have usually fused together completely.
The males have an additional age marker – the sagittal crest along
the top of their skulls begins to grow around age five and continues growing
until about age ten.
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Q: How
do you determine a sea lion’s age from its teeth?
DL: Sea lions secrete a new layer of cement on the insides of their
teeth each year. When one of these marine mammals dies, scientists can
look at a cross section of a tooth, much like they do with the growth
rings on trees, to determine its age.
Dr. Douglas
J. Long
Collections Manager and Acting Department Chairman
Department of Ornithology & Mammalogy
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Q: How
did this sea lion die?
RB: A fisherman’s gill net left an incriminating line of evidence
on this skull. The entangled youngster suffered a long cut along its brain
case and lived long enough for the bone to begin regenerating, but ultimately
it did not survive.
Raymond
Bandar
Field Associate
Department of Ornithology & Mammalogy
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What
is a Skull? |
Structure
& Function | Diversity
| Living
Tissue | Academy
Mission | Skulls
in Culture | Store
©
2002
California Academy of Sciences
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