View - Kowalewski, M. - Virginia Tech

VERMEIJ—EVOLUTION IN THE CONSUMER AGEForcible entry by seastars may not have reappeareduntil the Early Jurassic evolution of asteriids(Blake, 1990). Latrogastropods, many of whichhave the ability to insert their proboscis into preyshells, with or without the use of force or venom,evolved in the Early Cretaceous (Riedel, 2000).Those that use force, including Miocene to Recentbusyconine whelks, are evidently of more recentorigins (Vermeij, 1987; Dietl and Alexander, 1998).The application of venom by toxoglossans (asubgroup of latrogastropods) could have originatedas early as the Late Cretaceous. The labral tooth, astructure enabling some marine latrogastropods toincrease speed of subjugation, arose at least 58times independently beginning in the Campanianstage of the Late Cretaceous (Vermeij, 2001).Among top predators in the sea, there appearsto be a long-term trend evident within as well asamong clades toward increased speed andmaneuverability. Anomalocarids of the Early andMiddle Cambrian could swim, but probably not veryfast (Chen et al., 1994; Briggs, 1994). The earliestcephalopods, housed in chambered external shellsthat initially had their long axis oriented verticallyin the water, were likely to have been slowswimmers. So were horizontally oriented, mineralballastedcephalopods in straight shells, which interms of diversity dominated cephalopodassemblages from the Early Ordovician to the EarlyDevonian. Shell coiling, invented first during theEarly Ordovician but becoming common onlyduring the Early Devonian, probably increased boththe speed and maneuverability of cephalopods, butfurther radical improvements in locomotorperformance required a partial or complete freeingof the jet-propulsion mechanism of the animal fromthe confines of an external shell. This process beganin the Early Devonian with the evolution of earlysquid-like cephalopods, and accelerated during theMesozoic when the ammonoid body and jetpropulsivemusculature may well have extendedbeyond the body chamber of the external shell.Fast, highly maneuverable squid have become thecephalopod norm in post-Cretaceous times(Chamberlain, 1991; Jacobs, 1992). Amongvertebrates, conodont animals of the Ordovician,capable of cruising but not of sprint swimming(Purnell, 1995; Gabbott et al., 1995), weresuccessively replaced as top predators by faster,more maneuverable jawed acanthodians andelasmobranchs, bony fishes, and various Mesozoicand Cenozoic marine tetrapods. Even in the slowworld of gastropods, high speed among predatorsis a geologically young attribute in many clades.On land as in the sea, top predators increasinglyemphasized both rapidity of subjugation andlocomotor performance. Serrated teeth, forexample, efficiently slice flesh, and are both latein origin and evolutionarily derived in such groupsas sharks and dinosaurs (Abler, 1992; Currie,1997). The earliest venomous tetrapod is knownfrom the Triassic (Sues, 1991). Among snakes, theability to engulf prey of weight equal to or greaterthan that of the predator is a derived, probably LateCretaceous, character; and envenomation is evenmore recent, perhaps appearing in the Eocene(Greene, 1997).If top predators exercise disproportionateevolutionary control over the phenotypes anddistributions of prey and of the other species withwhich they interact, then the overall increase inpredatory performance over the long sweep ofPhanerozoic time has some important implicationsbesides the observed predator-prey escalation. As ageneral rule, the highest-performing consumers haveevolved in productive biotas comprising manyspecies with large populations and geographicranges. On land, Late Cretaceous and Cenozoiccenters of such evolution were concentrated in Asiaand Africa; in the sea, the Indo-West Pacific regionseems to have played this role, at least fromOligocene time onward. When predators evolvingin these privileged biotas spread to smaller,biologically less sophisticated biotas, they often haddevastating effects on vulnerable species, andperhaps even drove some of them to extinction.Humans exemplify this trend all too well. Ashominids spread out of Africa, we and ourdomesticated and otherwise dependent species—parasites, commensals, and weeds—have broughtabout the extinction of thousands of species, mainlythus far on islands, in lakes, and on small continents,387