View - Kowalewski, M. - Virginia Tech

PALEONTOLOGICAL SOCIETY PAPERS, V. 8, 2002evolved as a deterrent to drilling predation.However, it would be very important to know theenvironmental conditions of the origin anddiversification of corbulids; also, for thosecorbulids with more than one conchiolin layer,whether they are from “physiologically” morestressful environments, such as brackish water oranoxic environments. It would also be importantto know their cladistic relationships with respectto their environment and conchiolin form.SUMMARY DISCUSSION:AN EPISODIC HISTORYOF PREDATIONPredation in marine communities evolvedthrough several phases of intensification withminor setbacks following mass extinctions(Fig.14). The Permo-Triassic extinction crisisformed a major setback for all marine communities.This certainly included many predatory taxa (e.g.,many ammonoids, nautiloids, phyllocarids,predatory archeogastropods). However, certainmarine predators, notably bony fishes and sharks,seem to have been less strongly affected by thismajor extinction than were many benthicinvertebrates (Knoll et al., 1996). Thus, predatorsseem to have rebounded rather rapidly and by theMiddle Triassic a variety of new predator guildshad appeared, including decapod crustaceans withcrushing claws, and shell-crushing sharks and bonyfish. However, data from the Triassic regardingshell repair and drilling predation are almost nonexistent.New groups of carnivorous marine reptilesalso appeared in the Triassic, includingdurophagous placodonts, and piscivorous andperhaps cephalopod-eating pachypleurosaurs,nothosaurs, ichthyosaurs, and the first plesiosaurs.Ceratite ammonoids and some marine reptiles(e.g., placodonts, nothosaurs) became extinctduring Late Triassic crises. However, other lineages(e.g., ammonites, ichthyosaurs, plesiosaurs)survived to form the stem groups for new Jurassicradiations. The Jurassic to Early Cretaceous sawthe rise of malacostracan crustaceans with crushingchelae and predatory vertebrates—in particular, themarine crocodilians, ichthyosaurs, and plesiosaurs.Following a setback in the Late Triassic, predatorsmade a major re-advance in the mid-Mesozoic withthe evolution of new groups of decapods,ammonites, neogastropods, and teleost fishes, aswell as neoselachian sharks and marine reptiles.Some of these groups are thought to have beendurophagous, but that does not mean they ateexclusively molluscan prey. Limited data from thistime indicates that drilling predation existed, butoccurred at low very frequencies.The Late Cretaceous saw unprecedented levelsof diversity of marine predaceous vertebratesincluding pliosaurs, plesiosaurs, and mosasaurs.The great Cretaceous-Tertiary extinction decimatedmarine reptiles. Drilling and shell peelingfrequencies pick up in the Late Cretaceouscorresponding to the evolution of new durophagousand shell-drilling groups. The drilling frequenciesfrom this time are no different from those reportedfrom Cenozoic localities; indeed, drilling and shellrepair data from the later Cretaceous and Cenozoicshow no apparent trends.The Cretaceous-Tertiary mass extinctioneliminated all large marine predators, including themosasaurs, plesiosaurs, and many sharks and fish.Additionally, pterosaurs and early marine birdswere eliminated. However, many benthicinvertebrate and fish predatory groups survived;and during the Paleogene, predatory benthicinvertebrates showed a spurt of evolution withneogastropoda and new groups of decapods, whilethe teleosts and neoselachian sharks both underwentparallel rapid evolutionary radiations; these werejoined by new predatory guilds of sea birds andmarine mamals. Ultimately, many of the largevertebrate predator guilds were refilled by newlyevolved groups of marine mammals (cetaceans,pinnipeds) and birds (gulls, albatrosses, penguins).Despite the fact that a new suite of predatorsevolved in the Cenozoic, there are no apparentescalatory trends in durophagous predation.All of this would seem to suggest episodic, butgenerally increasing predation pressure on marineorganisms through the Mesozoic–Cenozoicinterval. Theoretically, there should have been a176