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Selective extinction of late Neogene bivalves on the temperate Pacific coast of South America

¹ Marcelo M. Rivadeneira. Section of Ecology, Behavior and Evolution, Division of Biological Sciences, University of California, San Diego, La Jolla, California 92093-0116. mrivaden{at}biomail.ucsd.edu
² Pablo A. Marquet. Center for Advanced Studies in Ecology and Biodiversity and Departamento de Ecología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Casilla 114-D, Santiago, C.P. 6513667, Chile; Instituto de Ecología y Biodiversidad (IEB), Casilla 653, Santiago, Chile; and National Center for Ecological Analysis and Synthesis (NCEAS), 735 State Street, Suite 300 Santa Barbara, California 93101-5504

We assessed selective extinction patterns in bivalves during a late Neogene mass extinction event observed along the temperate Pacific coast of South America. The analysis of 99 late Neogene and Quaternary fossil sites (recorded from 7°S to 55°S), yielding 2800 occurrences and 118 species, revealed an abrupt decline in Lyellian percentages during the late Neogene–Pleistocene, suggesting the existence of a mass extinction that decimated 66% of the original assemblage. Using the late Neogene data set (n = 59 species, 1346 occurrences), we tested whether the extinction was nonrandom according to taxonomic structure, life habit, geographic range, and body size. Our results showed that the number of higher taxa that went extinct was not different than expected by random. At first sight, extinction was selective only according to life habit and geographic range. Nevertheless, when phylogenetic effects were accounted for, body size also showed significant selectivity. In general, epifaunal, small-sized (after phylogenetic correction), and short-ranged species tended to have increased probability of extinction. This is verified by strong interactions between the variables herein analyzed, suggesting the existence of nonlinear effects on extinction chances. In the heavily decimated epifaunal forms, survival was not enhanced by widespread ranges or larger body sizes. Conversely, the widespread and large-sized infaunal forms tended to have lower probability of extinction. Overall, the ultimate extinction of late Neogene bivalve species along the Pacific coast of South America seems to have been determined by a complex interplay of ecological and historical (phylogenetic) effects.