HIr - Desert Magazine of the Southwest

Paddy—as I must call him because
he was not feeling strong enough to
tote his entire name—was not handsome
by our standards, but was so
remarkably adapted to his kind of life
that his class survived for more than
a hundred million years. He was an
invertebrate possessed of an external
skeleton—which meant that he lacked
backbone. Instead of being largely
wrapped around his bones, as we are,
he was neatly packed inside them.
His class name, Greek for "threelobed,"
was given because this outer
casing of chiten reinforced by lime
carbonate with flexible joints between
the segments, appeared divided longitudinally
into three lobes. He was also
in three sections latitudinally: head
shield, thorax and pygidium. The head
shield, which most often survives in
fossil form, was equipped with a very
effective mouth, and usually some form
of eyes. Thorax segments were embellished
with appendages for crawling
and swimming. Thus Paddy could
chase worms along a sea bed or hover
in the water, fanning his feathery
swimming limbs to set up currents
which brought food bits within reach.
Since Paddy had no more knowledge
of aging processes than of race, he
could not realize that he was a very
old trilobite and that he was cracking
up. He only knew that nothing seemed
appetizing this morning, and his segments
were very stiff and painful when
he tried to move them. It was strangely
difficult to brea'he through his limb
fringes. His wet greenish world seemed
unusually dim, too, and as the day
AMBOY CRATER/:
Upper Cambrian — ®
Lower Cambrian