View - Kowalewski, M. - Virginia Tech

WALKER AND BRETT—POST-PALEOZOIC PATTERNS IN MARINE PREDATIONPOST-PALEOZOIC PATTERNS IN MARINE PREDATION:WAS THERE A MESOZOIC AND CENOZOIC MARINEPREDATORY REVOLUTION?SALLY E. WALKER 1 AND CARLTON E. BRETT 21Department of Geology, University of Georgia, Athens, Georgia 30602 USA2Department of Geology, University of Cincinnati, Cincinnati, Ohio 45221-0013 USAABSTRACT—Mesozoic and Cenozoic evolution of predators involved a series of episodes. Predators reboundedrather rapidly after the Permo-Triassic extinction and by the Middle Triassic a variety of new predator guildshad appeared, including decapod crustaceans with crushing claws, shell-crushing sharks and bony fish, as wellas marine reptiles adapted for crushing, smashing, and piercing shells. While several groups (e.g., placodonts,nothosaurs) became extinct in the Late Triassic crises, others (e.g., ichthyosaurs) survived; and the Jurassic toEarly Cretaceous saw the rise of malacostracan crustaceans with crushing chelae and predatory vertebrates—inparticular, the marine crocodilians, ichthyosaurs, and plesiosaurs. The late Cretaceous saw unprecedented levels ofdiversity of marine predaceous vertebrates including pliosaurids, plesiosaurs, and mosasaurs. The great Cretaceous-Tertiary extinction decimated marine reptiles. However, most invertebrate and fish predatory groups survived; andduring the Paleogene, predatory benthic invertebrates showed a spurt of evolution with neogastropods and newgroups of decapods, while the teleosts and neoselachian sharks both underwent parallel rapid evolutionary radiations;these were joined by new predatory guilds of sea birds and marine mammals. Thus, although escalation is sometimescast as an ongoing “arms race,” in actuality the predatory record shows long interludes of relative stabilitypuncturated by episodes of abrupt biotic reorganization during and after mass extinctions. This pattern suggestsepisodic, but generally increasing, predation pressure on marine organisms through the Mesozoic-Cenozoicinterval. However, review of the Cenozoic record of predation suggests that there are not unambiguous escalatorytrends in regard to antipredatory shell architecture, such as conchiolin and spines; nor do shell drilling and shellrepair data show a major increase from the Late Mesozoic through the Cenozoic. Most durophagous groups aregeneralists, and thus it may be that they had a diffuse effect on their invertebrate prey.“As evolutionists, we are charged, almost bydefinition, to regard historical pathways as theessence of our subject. We cannot be indifferent tothe fact that similar results can arise by differenthistorical routes.” —Gould and Vrba, 1982“This is not to say that selection is notimportant, but that its invocation is not justifieduntil the role of chance in the operation of abasically stochastic universe is ruled out.”—Schram, 1986“A science grows only as it is willing toquestion its assumptions and expand itsapproaches.” —Hickman, 1980INTRODUCTIONTHE CONCEPT OF predator-prey escalationis, in large measure, an outgrowth of the extensivestudies of Vermeij (1977, 1987) on the so-called“Mesozoic Marine Revolution.” This term mightseem to imply that a dramatic development ofmarine predators was initiated at the Triassic; acontinuous intensification of predator-preyrelationships has been envisaged. In actuality, theMesozoic and Cenozoic evolution of predatorsinvolved a series of episodes. In this paper wedocument the diverse predatory guilds of theMesozoic and Cenozoic, especially vertebrates thatputatively devoured invertebrate prey, withcomments on their modes of feeding and possible119