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PALEONTOLOGICAL SOCIETY PAPERS, V. 8, 2002abFIGURE 7—Comparison of predatory with non-predatory gastropods. (a) Comparison of genus diversityof all gastropods with the genus diversity of predatory gastropods. (b) Proportion of genus diversity ofgastropods comprised of predators.330
BAMBACH—SUPPORTING PREDATORScommon in some mesogastropod groups (naticids).More “aggressive” strategies effective against moreactive prey, such as “harpooning” prey withmodified radular teeth and injecting poison, aspracticed by cone shells, or using shell features toaid in actively prying open the shells of prey, onlybecame common in the Neogastropoda (Hyman,1967). The Late Cretaceous burst of diversificationof Neogastropods is one of the reasons the MesozoicMarine Revolution noted by Vermeij (1977) isexpressed most strongly in the later Cretaceous.The limitations of the database, which includesno information on relative (or absolute) abundance,must again be emphasized. The increase indiversity of predatory gastropods to the point atwhich they are more diverse than non-predatorsmust say something about the ability of gastropodpredators to specialize, thus adding diversity asprey biomass can support it, but it says nothingabout the abundance of predators per se, nor aboutthe number of predator individuals compared toprey. Tabulations, such as those made by GwenDaley (Daley, 1999; Daley and <strong>Kowalewski</strong>, 2000)indicate that in Cenozoic deposits most predatorygastropod species are rare compared to suspensionfeeding forms and bivalves.Cephalopods.—The diversity of cephalopods,an exclusively predatory class, is remarkable in nottrending up or down from the later Ordovicianthrough the Cretaceous despite the great volatilityof the group as a whole (Fig. 8a). This volatility isapparent in the fluctuations of continuing standingdiversity coupled with the high rate of withinintervalturnover. Total diversity of cephalopodswithin intervals was often more than twice theboundary-crossing standing diversity. The rapidturnover implies rapid evolution, which is attestedby the utility of cephalopod fossils forbiostratigraphy. Figure 8b shows the shift over timein diversity dominance from all nautiloids (varioustetrabranch groups) in the Ordovician, to aboutequal diversity of ammonoids (phylogeneticallyallied with the dibranch coleoids; Engeser, 1990,1996; Jacobs and Landman, 1993) and nautiloidsin the Late Paleozoic and Triassic, to diversitydominance by ammonoids in the Jurassic andCretaceous. Belemnites, present only in theMesozoic, are also grouped with the coleoids. Theextinction of ammonites and belemnites at the endof the Cretaceous reduced the fossil record ofcephalopod genus diversity dramatically, but thenumber of living families, over 30, is about thesame as the average number of families recordedthrough much of the Phanerozoic (Sepkoski, 1982,1992). Elsewhere I have suggested that theprogressive change in diversity dominance incephalopods may have been related to improvedswimming control driven in part by the evolutionof other swimming competitors such as the variousfish groups (Bambach 1985, 1999). Themaintenance of diversity, but with no increase overtime, implies that cephalopods were able to fillsome portion of ecospace well, but not capture newecospace or specialize beyond their initialcapabilities (Bambach, 1985).Arthropods.—Many different classes in thearthropods contain predators: arthropod-likeanimals of unknown affinities, such asanomalocarids; trilobites; eurypterids; andmalacostracans. The jaws and pincers of many ofthese taxa attest to their predatory nature. Trilobiteshad relatively undifferentiated limbs and have oftenbeen thought to have been predominantly depositfeeders, but recent work has shown that many werelikely predators (Fortey and Owens, 1999; Fortey,2000). The diversity of predatory arthropodsfollows a different pattern than that of thecephalopods. Predatory arthropods have highdiversity in the Early and Middle Paleozoic, whichstarts to fade in the mid Devonian and reaches alow level through the Permian and Triassic beforerising continuously from the Jurassic to theHolocene (Fig. 9a). Relatively high diversity wasachieved earlier than for any other predatory groupwith the arthropod incertae sedis (which includesa variety of “stem group” arthropods, such asAnomalocaris and Opabinia from the BurgessShale); and then trilobites diversified in theCambrian (Figs. 10a, 10b), and although overalltrilobite diversity after the end-Ordovicianextinction never recovered its Late Ordovicianlevel, the success of the eurypterids in the Silurian331
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THE PALEONTOLOGICAL SOCIETYPAPERSVo
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The Paleontological Society Special
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AuthorsRICHARD K. BAMBACHBotanical
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THE FOSSIL RECORD OF PREDATIONMicha
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INTRODUCTIONTHE FOSSIL RECORD OF PR
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KOWALEWSKI—ANALYTICAL METHODSTHE
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THE PALEONTOLOGICAL SOCIETY PAPERSP
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