The class Trilobita belongs to the phylum Arthropoda. The distinguishing features
of arthropods are an exoskeleton of chitin which is sometimes calcified, a segmented body
and jointed appendages. Trilobites molted to conform exoskeleton to new bodysize with
growth. Only the dorsal part of the exoskeleton calcified so that is what fossils of
trilobites represent. Trilobites were benthic, epifaunal and vagile creatures. They
moved in the water column just above the sea floor. They were deposit feeders.(Thompson 1997)
The warm, shallow, sunny waters of the early
Paleozoic were favorable for the development of trilobites at the end of the Precambrian
and explosion at the beginning of the Cambrian. By late Cambrian and early Ordovician,
the trilobites were declining since many other creatures had developed and were infilling
the niche once occupied by trilobites and a few other creatures.
In Ottawa, Isotelus and Flexicalymene species of
trilobites have been found.