Trends in Body Size Evolution of Devonian and Mississippian Fishes
Galimberti, Andrew K.
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The Devonian (419-359 million years ago), known as the “Age of Fishes,” was the time of a great radiation of fishes. The end of the Devonian saw the occurrence of the Hangenberg event, a mass extinction which decimated some of the most dominant fish taxa, allowing for the emergence of new fish diversity in the Mississippian (Early Carboniferous; 359-323 million years ago). In the present study, body sizes of 1,134 fish species were analyzed to examine how these evolutionary events affected fish body sizes. The study focused primarily on two trends: Cope’s Rule, or the tendency for body sizes to increase over time; and the Lilliput Effect, the decrease of body sizes following a mass extinction. The results show that body sizes consistently increased throughout the Devonian, providing evidence for Cope’s Rule. Models suggest size increase in the Devonian was an active, selection-driven trend. The Lilliput Effect was observed among most fish, but some groups remained large or increased in size, suggesting bimodal survival. Contrary to previous studies, oxygen and temperature were not related to body size changes.