Geology Reference
In-Depth Information
Trilobites are
arthropods,
which today include insects, spiders, and crusta-
ceans such as lobsters. Species of trilobites filled every nook and cranny of the
ocean throughout the Paleozoic, but they did not survive the end-Permian extinc-
tion. (I discuss this and other extinction events in Chapter 22.)
Trilobites had an exoskeleton that is segmented into parts, similar in appearance to roly
polys (pill bugs) but with a horseshoe-shaped head segment. They ranged in size from
itty bitty (just a few millimeters) to more than 50 centimeters (almost 2 feet) in length,
but most of them were around 5 to 10 centimeters (about 3 to 4 inches). Some were
blind, others had compound eyes (like some insects today), and certain species could
roll up just like a roly poly, presumably for protection. A collection of trilobites are pic-
tured in this topic's color photo section and illustrated in Figure 19-1.
While trilobites continued to cover the seafloor throughout the Paleozoic, they were
most diverse during the Cambrian period and begin to be overshadowed in the fossil re-
cord by the development of other types of creatures later in the Paleozoic.
Figure 19-1:
A
trilobite.
Building Reefs All Over the Place
Early Paleozoic life was lived under the sea. Many of the large continents at the time
were occasionally (meaning for a few million years at a time) covered by shallow seas,
called
epeiric
or
epicontinental
seas. This expansive undersea environment meant that
