Biogeographic patterns in Late Paleozoic trilobites

Abstract

Based on cluster and correspondence analysis, Late Paleozoic trilobites are shown to display varying degrees of provincialism and cosmopolitanism through time. These distributional changes appear to coincide temporally with the closing of the Rheic Ocean and the onset and waning of the Late Paleozoic Ice Age. Early Tournaisan trilobite faunas, composed mainly of primitive phillipsid genera, display widespread distribution within ancestral deep-water environments of the Rheic Ocean. Middle to late Tournaisian through early Viséan trilobite genera were segregated into environmentally constrained endemic shelf faunas, and widespread to cosmopolitan deep-water biota. Reduced provincialism during the Serpukhovian is interpreted to have resulted from the onset of the Late Paleozoic Ice Age. Initiation of this profound global environmental perturbation is interpreted to have produced equatorially constricted climate zones and rapidly vacillating sea level and cylothemic deposits that created high levels of ecological stress within marine faunas. Early Pennsylvanian trilobite faunas exhibited weak levels of provincialism on either side of Pangea, with dominant faunal components displaying cosmopolitan tendencies. Trilobite faunas of the late Pennsylvanian were characterized by a few widespread to cosmopolitan genera, that exhibit ecologic generalist tendencies while inhabiting broad geographic and latitudinal ranges. Permian trilobites exhibit a progressive increase in provincialism through time which is interpreted to be the result of the ending of the Late Paleozoic Ice Age and the onset of greenhouse conditions.