We are interested in how to use fossil shape to tell us neat things about the evolutionary process and about interesting episodes in Earth's history. The Cambrian Radiation 540 million years ago, at the base of the Cambrian time period, there was an explosive diversification in the variety and abundance of animals living in the Earth's oceans. While we have learned a tremendous amount from these unique windows of preservation, the exceptional nature of these deposits prevents us from examining the diversification of the soft-bodied fossil groups in detail, because we only see such fleeting glimpses of their evolutionary histories. Trilobites have a special advantage in this regard because their resistant hard skeletons present us with a quality fossil record throughout most of Paleozoic time. This abundance of trilobite fossils allows us dissect their evolutionary history in detail.
Trilobites are by far the most abundant of all skeletonized Cambrian metazoans.
This fact reflects the volumetric and taxonomic abundance of trilobites in a wide range of Cambrian sediments, their intricate and labile morphology, and their occurrence throughout the majority of Cambrian time. These attributes have given the group unrivaled utility as zonal fossils in Cambrian strata, and as the principal faunal element used in Cambrian paleobiogeography. Paradoxically, while trilobites serve as the timekeepers by which we gauge the evolution of other Cambrian metazoans, many aspects of the evolutionary radiation of trilobites remains poorly resolved. One of the great problems of the Cambrian explosion is to explain how such diversity was generated so quickly. Others suggest that the diversification is a natural consequence of the empty ecological space available in the Cambrian.