View - Kowalewski, M. - Virginia Tech

CLOSING REMARKSMajor groups of amniote predators such astheropod dinosaurs and carnivorous synapsids offera continuous fossil record of predator-preyinteractions in the terrestrial realm. The fossilrecord of predatory theropod dinosaurs suggeststhat the taxonomic composition of dinosaurianpredator-prey systems varied notably as a functionof time and geography (Farlow and Holtz). Detailsregarding diet and hunting behavior of theropodscan be inferred from their functional morphology,supported by evidence from taphonomicassociations with likely prey species, bite marks,gut contents, coprolites, and trackways (Farlow andHoltz). Following the K-T extinction, carnivorousbirds (the direct descendants of theropods)remained prominent predators throughout theCenozoic Era (Farlow and Holtz).The fossil record of synapsids points tosignificant parallels between the diversification ofnon-mammalian synapsid predators in the LateCarboniferous–Triassic and the Cenozoicradiation of mammalian predators: both groupsevolved sabertooth forms as well as short-snouted,powerful biting forms (Van Valkenburg andJenkins). Both radiations are characterized byrepeated patterns in which one or a few cladesevolved large size and dominated the carnivoreguild for several million years, but then declinedand were replaced by new taxa (Van Valkenburghand Jenkins). Both non-mammalian andmammalian synapsid clades show trends towardincreasing body size and hypercarnivory over time(Van Valkenburgh and Jenkins).PROCESSESThe last part of this volume includes chaptersthat provide an introduction to some major modelsregarding the origin and history of predation as wellas the evolutionary role of predator-preyinteractions through time.Although data on early life are understandablyscarce, existing data and theoretical considerationssuggest that predation may have played animportant role in some of the major transitions inevolution, including the origin of eukaryotic cells,the origin of multicellularity (as a means ofacquiring larger size), the decline of stromatolites,the diversification of acritarchs, and the Cambrianexplosion (Bengtson; see also Lipps and Culver).Predation may have been a decisive selective forcebehind the transition from simple, mostly microbial,ecosystems to those with complex food webs andhigher-order consumers (Bengtson; Lipps andCulver). Following the Cambrian explosion, thediversity of predators and the proportion of the totalfauna represented by predators have both increasedthroughout the Phanerozoic, implying thatecosystems have increased their ability to supporteither more predators or more specialization amongpredators (Bambach). This pattern may be linked toa secular increase in diversity and biomass ofprimary producers, and changes in the compositionof prey taxa (Bambach).The evolutionary importance of predationremains a hotly debated topic. Arms races betweenpredators and prey may be driven by two relatedprocesses: escalation—enemy-driven evolution, inwhich the role of prey in the evolution of thepredator is downplayed—and coevolution—inwhich two or more interacting species respondreciprocally to one another; prey are thought todrive the evolution of their predator, and vice versa(Dietl and Kelley; Vermeij). In the fossil record,the two processes are distinguished most reliablywhen the predator-prey system is viewed within thecontext of the other species that may influence theinteraction, thus allowing for a relative ranking ofthe importance of selective agents (Dietl and Kelley).Scale is also important in evaluating the role ofescalation and coevolution in the development ofspecies interactions: prey are likely to exert someselective pressure on their predators over ecologicaltime scales, but predators may still exert primary“top-down” control in directing evolution overevolutionary timescales. In the long term, predatorshave two principal effects: they influence preyphenotypes and they restrict prey to environmentswhere predators are rare (Vermeij). Predators likelycontrol overall directionality in evolution becauseof the inequalities of predator and prey in control ofresources (Vermeij; Dietl and Kelley). Indeed,predators have the evolutionary upper hand over397