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PALEONTOLOGICAL SOCIETY PAPERS, V. 8, 2002stereotypical positioning on valves (see Fig. 4.5),as is typical for predatory gastropods (Ausich andGurrola, 1979; Smith et al., 1985; Leighton, 2001a).As with durophagous predation, there is evidencefor intensification of shell drilling in the Devonian(Kowalewski et al., 1998), although the fossil recordof platyceratids shows relatively little increaseduring this time. Initially, it was thought that thefrequency of drilling declined in the late Paleozoic(Kowalewski et al. 1998), and this seems to besupported in some cases (Kowalewski et al., 2000;Hoffmeister et al., 2002). However, for individualspecies data, drilling frequencies can be similar tothose reported for the Late Cretaceous to Cenozoic—which can exceed 30% per species examined (Ausichand Gurrola 1979; Hoffmeister et al. 2001a, b).Asteroids.—Asteroids evidently developed theirnotoriously predaceous habits early in their history(Blake and Guensburg, 1992). Middle Ordovicianstarfish have been found with gastropod shells intheir gut cavities (Spencer and Wright, 1966). Stillolder possible examples of starfish predation areknown from as early as the Whiterockian (MiddleOrdovician; G. C. Baird, pers. comm.).There is controversy as to whether or not starfishdeveloped extraoral digestion in the Paleozoic (seeDonovan and Gale, 1990). However, Blake andGuensburg (1994) describe an OrdovicianPromopalaeaster in apparent feeding position on abivalve, a characteristic behavior related to extraoraldigestion. Similarly, Clarke (1921) illustratedprobable examples of starfish predation from theDevonian of New York, where specimens ofDevonaster apparently were overwhelmed bysediment while in feeding position on bivalves.Gnathostomes.—The earliest well-knownpredatory gnathostome fishes are Silurianacanthodians, although possible acanthodian spinesand chondrichthyan (shark) denticles are known fromthe Middle Ordovician (Benton, 1997). These fishesand their later Paleozoic descendants possessed sharpteeth with cutting plates adapted for predation on softto chitinous invertebrates and other fishes.The earliest major radiation of durophagous(shell-crushing) fishes undoubtedly occurred in theEarly to Middle Devonian. Varied placoderms,including rhenanids with blunt crushing plates andray-like benthic adaptation, and ptyctodonts withhypermineralized tritors, also evolved during theDevonian. The ptyctodonts and rhenanids mayhave been important crushers of hard-shelled prey(Figs. 5.1, 5.2), although their remains areuncommon in most marine invertebrate-richassemblages. Nonetheless, there are reports ofptyctodonts in normal marine shell beds (Moy-Thomas and Miles, 1971). Ptyctodonts, in fact, aremost commonly associated with fragmentaryremains of arthrodires. Their blunt, crushing teethmay have been adapted for cracking the armor ofarthrodires during scavenging.Placoderms became extinct by the end of theDevonian (Moy-Thomas and Miles, 1971), but werereplaced by varied sharks (Fig. 6). Especially duringthe Carboniferous and Permian, many types of sharksevolved, including the symmoriaformes, hybodontids,and ctenacanthoids, some of which developedbroadened teeth and were durophagous (Moy-Thomas and Miles, 1971; Mapes and Benstock, 1988)(Fig. 6). For example, Boyd and Newell (1972) reporta high percentage of Permian bivalves with divots inthe shells probably produced by sharks (see Fig. 4.2).Chimaeras or holocephalans (e.g., helodontoids,cochliodontoids, and petalodontids) possessedautostylic (fused) skulls and hypermineralized,crushing dentition analogous to that of earlierptyctodonts (Fig. 6.4). Certain Carboniferouschimaeras, such as Helodus, have been implicated asproducers of distinct crush marks in Carboniferousand Permian brachiopod and bivalve shells (Brunton,1966; Boyd and Newell, 1969; Alexander, 1981).Hansen and Mapes (1990) also reported crush marksin Upper Carboniferous nautiloids that theyattributed to the shark Petalodus (Fig. 3.7).Chimaeroids underwent a five-fold increase intaxonomic richness in the Carboniferous relative tothe Devonian (Mapes and Benstock, 1988). However,durophagous holocephalans also underwent a majordecline in the Upper Carboniferous and Permian(Mapes and Benstock, 1988).In addition, during the Carboniferous, deepbodiedchondrostean fishes of the Doryopteridaedeveloped well-defined tooth plates for crushing102