Phylum Arthropoda, Class Trilobita

Cambrian.  The first appearance of trilobites defines the start of Series 2 of the Cambrian, and they can be found in strata up to the upper Permian, after which trilobites (among a large number of marine organisms) went extinct in the great catastrophe that removed over 90% of all species on earth. The greatest numbers of trilobite species occurred during the Cambrian and Ordovician periods, after which trilobite extinction trends exceeded radiation events.
Abstract/Description: Cambrian. The first appearance of trilobites defines the start of Series 2 of the Cambrian, and they can be found in strata up to the upper Permian, after which trilobites (among a large number of marine organisms) went extinct in the great catastrophe that removed over 90% of all species on earth. The greatest numbers of trilobite species occurred during the Cambrian and Ordovician periods, after which trilobite extinction trends exceeded radiation events.
Subject(s): Ontario, Canada
environmental sciences