Meeting Abstract
Historically, most analyses of “mass extinctions” have focused on the marine realm, because most fossils are preserved there and marine sediments provide more and finer-scaled evidence of turnover and crises in biodiversity than terrestrial environments do. Because marine taxa outnumber terrestrial taxa by a margin of at least 25:1, analyses of diversity crises that have lumped all phyla and environments together, especially at the global level, have caused the terrestrial evidence to be “swamped” statistically by the marine data. Both synchroneity and causality of terrestrial and marine events have usually been assumed, without decisive data. The concept of “mass extinctions” has no definitional limits on the application of the term with respect to duration, geography, ecology, or taxa affected. Such events have little comparability, no operational definitions, and inadequate underpinnings in testable theory. Unusual drops in taxonomic diversity have traditionally focused only on increases in extinction rates, with scarce consideration (if any) of origination rates and their interplay with extinction rates. As a result, some major episodes in the history of life have been largely misinterpreted, notably the loss of some terrestrial animal groups at the end of the Permian, the Triassic, and the Cretaceous. The present diversity crisis is nothing like those of the past, and cannot be studied in the same way. Analyses of hypothesized diversity crises should be operationally and situationally defined and statistically normalized through the histories of taxa and biotas, and should always explicitly include both origination and extinction rates. The term “mass extinctions” should be abandoned and replaced by “diversity crises.” These parameters require not absolute numerical (or percentage) limits but situational ones.
