Back to the Phylum Arthropoda

TRILOBITES
Trilobites are one of the most successful Paleozoic groups. Because of their diversity and continued evolution they are one of the better groups for time zonation.

Perenopsids are a group of small blind trilobites. This specimen is actually less than  1.5 cm long (about 1/2 in.)
Others were much larger. This trilobite is some 20cm 
(~8 in.) in length.
This is a detail of the trilobite above. Note that the trilobites had already evolved compound eyes, still used today by their relatives, the insects.
Others developed bizarre and ornate horns.
This is Phacops rana a common North American trilobite.