Escalation and its role in Jurassic biotic history

The hypothesis of escalation asserts that enemies — competitors, predators, and pathogens — drive much of adaptive evolution. In a critical review of methods for testing this hypothesis, I argue that enemy-related adaptations of individuals and other units of evolution must be evaluated through time in physically similar environments, and that tests relying on global changes in diversity are inadequate and misleading.The later Mesozoic era — the Jurassic and Cretaceous periods in particular — had been seen as a time of substantial worldwide escalation. New analyses of the times of origin of 46 escalation-related innovations indicated that the latter are concentrated during the Late Triassic to Early Jurassic and in the mid to late Cretaceous. The Jurassic was a time of consolidation, when clades whose members are well adapted to environments rich in enemies underwent rapid and sustained regional diversification in tropical settings. These radiations, which continued into the Cretaceous, were accompanied by relatively low levels of extinction.