Assessing trilobite biodiversity change in the Ordovician of the British Isles

The Ordovician Period saw the most sustained, steep rise in marine biodiver sity in the history of life on Earth and set the ecological pattern for the rest of the Palaeozoic Era. The long history of research, wide variety of depositional settings and juxtaposition of terranes with very different pal aeobiogeographical histories makes the Ordovician of the British Isles an e xcellent laboratory in which to study this change. A database approach to a nalysis of trilobite biodiversity change is described using a simple compil ation of stratigraphical ranges of 663 species of Avalonian trilobites, and a much more sophisticated information-rich relational database based on th e fundamental information of the fossil record-species at localities. The l atter includes 2001 occurrence records of 617 trilobite species at 508 loca lities in the Welsh Basin. The first ever species-level diversity curves fo r the whole Ordovician of an entire region are presented. Both databases re veal an overall increase in species- and genus-level diversity through the Ordovician. Random resampling tests and environmental information are used to remove sampling effects from the Welsh Basin diversity curves. The main features of trilobite biodiversity change in Avalonia are the following: a late Arenig-early Llanvirn increase, during which time the highest species- to-genus ratios occur, is contemporaneous with a rise in global diversity a nd rifting of Avalonia from Gondwana; a late Abereiddian dip is followed by recovery during the Llandeilian-early Caradoc; decline during the late Car adoc-early Ashgill is at least partly attributable to lack of preserved roc k and restriction of most of the preserved faunas to deep-water environment s. The greatest diversity occurs in the palaeoenvironmentally differentiate d Rawtheyan and is followed by the diversity crash seen in the Hirnantian t hroughout the world. Copyright (C) 2001 John Wiley & Sons, Ltd.