They had a high rate of evolution during the Cambrian, Ordovician and Silurian periods. The composition of the faunas changed many times so that many zones are recognized. At the same time, the above organisms were abundant and widespread. This has made it possible to correlate faunas of the same age over great distances. Rocks of different ages can strongly resemble each other, particularly when the original sediments were deposited in similar environments.
Fossils therefore provide an elegant way to quickly discriminate between various rock units.
The current oil and gas exploration underway in western Newfoundland is a direct consequence of the more detailed stratigraphy made possible by biostratigraphic control. This is because the two areas were originally in different climatic zones on opposite sides of an ancient ocean called Iapetus. Continental drift later brought the two areas together. These faunas collectively belong to what is called the Acado-Baltic faunal province. Eastern Newfoundland is one of the best places in the world to examine Acado-Baltic trilobites.