PHANEROZOIC TRENDS IN ECOLOGICAL DIVERSITY OF MARINE ANIMAL TAXA

Mollusks, arthropods, echinoderms, and chordates are the ecologically most diverse and functionally most disparate animal clades on earth today. Has this pattern held true since their origins? Or are critical external events or essential internal factors responsible for their lead? Here, I use updated codings of ecological life habits for all known Phanerozoic marine animal genera from the Paleobiology Database in a standardized ecospace framework. These codings allow quantitative comparisons of how different major taxa (phyla and classes) varied across their Phanerozoic histories, with ecological (functional) diversity evaluated using two measures: ecological richness (the number of unique life habits) and disparity (mean Euclidean distance).

Mollusks and arthropods (and to a lesser extent their classes) have always been the most ecologically rich and disparate, and most clades have maintained relatively consistent levels of ecological diversity throughout their history. But the trajectory for many clades is more varied. At their origins, chordates had very low richness and disparity, but diversified significantly during the Devonian radiation of fishes and again after the Permian mass extinction. Echinoderms achieved peak richness during the Paleozoic, but have increased disparity during the post-Paleozoic as their ecologically distinct modern classes diversified. Overall, there is little impact at these broad scales for mass extinctions in resetting most clade trajectories, and there is also generally low correlation with these trends and that of genus richness. These patterns suggest deep and inherent constraints to ecological innovation in most clades, presumably largely set during their origins and little influenced by subsequent mass extinctions and by turnover by ecologically similar clades.

This research has been supported by NSF grant #2322080.