The "Age of Trilobites" and the Cambrian
The most abundant and diverse animals
of Cambrian time were the trilobites. Trilobites
had long antennae, compound eyes, many jointed legs, and a hard
exoskeleton like many of their modern arthropod relatives, such
as lobsters, crabs, and insects. The Cambrian is sometimes called
the "Age of Trilobites" because of their explosive diversification
into all marine environments worldwide. In size, they ranged from
a few millimeters (1 mm = 0.25 inches) to 45 centimeters (18 inches).
Following the Cambrian, trilobites remained an abundant and diverse
element of Ordovician marine faunas, but other groups of organisms
that had been more minor elements of Cambrian faunas diversified
dramatically. These include snails, clams,
brachiopods, cephalopods, corals,
bryozoans, and the now extinct graptolites.
This post-Cambrian radiation, the Paleozoic Fauna,
would dominate marine life until the end of Permian time.