View - Kowalewski, M. - Virginia Tech

PALEONTOLOGICAL SOCIETY PAPERS, V. 8, 2002as an evolutionary unit, was accompanied by themajor innovation of phagocytosis, which enablesone organism to envelop—effectively to swallow—another individual completely (Margulis, 1981;Knoll and Bambach, 2000). Eukaryotic organizationevidently existed by 2.7 billion years ago and maywell be even older. Consumption of smallerprokaryotic and eukaryotic organisms by largersingle-celled consumers in the so-called microbialloop may have been the norm through much of theMesoproterozoic and Neoproterozoic eras(Butterfield, 1997). The date of origin ofmulticellular animals remains highly controversial,as does the time of appearance of structures thatwould allow such multicellular animals to ingest orotherwise to consume other multicellular life forms.The earliest evidence of successful as well asunsuccessful predation on animals comes from thelatest Neoproterozoic of Namibia. Bengtson andZhao (1992) described complete and incompleteholes excavated by an unknown attacker in themineralized tubular fossil Cloudina. This kind ofpredation persisted into the Early Cambrian(Conway Morris and Bengtson, 1994). At least twoadditional means of consumption—suspensionfeedingand predation by skeletal breakage—maketheir first appearance no later than the EarlyCambrian. Trilobites of this age show skeletalbreakage and repair consistent with the hypothesisthat anomalocarid arthropods, which at a length ofone meter or more are the largest known animalsof the time, were the culprits (Chen et al., 1994;Briggs, 1994; Collins, 1996; Babcock and Robison,1989). Suspension-feeding animals, whichconsume small prey en masse by collecting andfiltering them out of the water, also appeared inthe Early Cambrian (Vannier and Chen, 2000).Fossils preserved in the Burgess Shale (MiddleCambrian) of British Columbia reveal predationinvolving the ingestion of those undamaged pelagicprey by larger predators (Conway Morris, 1979).Thus, at least four distinct modes of predation wereestablished no later than Middle Cambrian time,about 525 Ma. Many adaptations of prey, notablyskeletonization and the evolution of spines, aredemonstrable antipredatory adaptationsrecognizable from latest Neoproterozoic timeonward (Vermeij, 1989). It is also likely thatevolutionary invasions by many lineages into theinfaunal environment (beneath the surface ofsediments), the pelagic realm, and even theendolithic environment (beneath the surface ofrocks) were prompted by the appearance anddiversification of consumers during the openingphases of the Phanerozoic Eon (Vermeij, 1987).PHANEROZOIC TRENDSAND THEIR IMPLICATIONSPatterns in the intensity of successful andunsuccessful predation and in the adaptationsrelated to predation are discernible at two distinctand complementary levels. The first is the level ofindividual lineages or clades, which are tracedthrough time in physically similar environments,that is, environments in which such characteristicsas thermal regime, productivity, and sediment typeremain more or less the same over the intervalconsidered. This level also accommodates lineagereplacement, as long as the replacing and replacedlineages share a common adaptive syndrome, oradaptive style. The second level ismacroevolutionary. Within assemblages fromsuccessive, environmentally similar horizons, wecan track the relative representation of variousadaptive syndromes. For example, the incidenceof species emphasizing resistance defenses ofvarious kinds can be compared to the incidence ofspecies emphasizing adaptations at the pursuitphase of predation. These macroevolutionarypatterns arise from differences in the rates ofspeciation or extinction of clades differing inadaptive style, and from replacement of cladesemphasizing one style of adaptation with cladesemphasizing another. My interest in predator-preyescalation was aroused by temporal patterns of thiskind in the expression of shell armor in molluscs(Vermeij, 1975). An increase in breakage-resistantspecies, and a decrease in the proportion of specieswith predation-vulnerable architecture, led me tothe hypothesis that breakage became anincreasingly important agency of selection through382