Extinction selectivity and ecology in planktonic foraminifera
Abstract Planktonic foraminifera have radiated three times since the mid-Cretaceous and independently evolved similar morphological groups and patterns of species longevity in each diversification. All morphological groups include substantial numbers of short-ranging species, but only some groups include large numbers of long-ranging taxa. The long ranges of these ‘extinction-resistant’ taxa are unlikely to be due to systematic differences in geographic range, body size, or taxonomic practice. Instead, life history traits such as trophic ecology and factors influencing population structure are closely correlated with species longevity during each of the radiations. Generation time and reproductive output are correlated with longevity in living species but the significance of these factors for extinct taxa is unknown. Other variables such as depth distribution are inversely correlated with longevity in Neogene and Cretaceous biotas, but not in Paleogene foraminifera. Perhaps the ability to use a wide variety of food types and maintenance of large populations contribute to extinction resistance. It is possible that these traits are correlated with life in geologically persistent watermasses. Indeed, long-ranging species are concentrated in geologically old, stable environments in the oligotrophic gyres and waters below the thermocline. In contrast, species that live in ephemeral boundary layers are frequently short-ranging. It may be the stability and trophic conditions in water-masses have been the ultimate arbitrators of species longevity.