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PALEONTOLOGICAL SOCIETY PAPERS, V. 8, 2002Myliobatis stomach contents vary ontogeneticallyand with the sex of the ray (Gray et al., 1997). Inthe study by Gray et al. (1997), juvenile bat raysfed on small clams (< 5 mm clam siphon diameter),benthic shrimp, and polychaetes. Adult rayspredominately fed on polychaetes, large clams(>5mm clam siphon diameter), and Cancer crabs.The largest rays preferred large clams and Cancercrabs. Large clams and crabs were eaten by adultfemale rays, whereas subadult and adult male raysfed primarily on polychaetes and burrowing shrimp.In other studies, large females also predominantlyfed on echiuran worms (Karl and Obrebski, 1976).Rays and skates excavate shallow pits in softsediments in search of prey (Fig. 12) (Gregory etal., 1979). The cownose ray (Rhinoptera bonasus)and possibly other batoids repeatedly inhalesediments and water through the mouth and ventit out the gill slits; the pectoral fins act to move theFIGURE 12—Benthic feeding by batoid rays.Upper figure, diagram of eagle ray Myliobatis jettingwater through gill slits to excavate circular feedingdepression. Lower figure, drawing of ray in feedingposition on excavated pit. From Gregory et al.(1979) and Howard et al. (1977).sediment away and to enlarge the burrow (Gray etal., 1997). Similar shallow pits are present inPleistocene localities, and are indicative of rayfeeding activities (Fig.12) (Howard et al., 1977).These pits could be correlated with associatedfragmented mollusc deposits, but, to date, this hasnot been examinedPods of deep-water gastropods attributed toeither fecal masses or regurgitated remains fromshell-eating sharks or other predators, weredescribed from bathyal Pliocene deposits fromEcuador (Hasson and Fischer, 1986, p. 35).However, a recent analysis of these shell “nests”revealed that they are not related to predation(Walker, 2001).Osteicthyes.—The diversification of teleosts(Fig. 11.1) in the Cenozoic is unprecedented amongvertebrates: presently some 23,670 species areassigned to 38 orders and 425 families (Patterson,1994). This is largely the result of development oftwo clades during the Cenozoic, the Ostariophysiin fresh water and the very successfulAcanthomorpha (over 21,000 extant species) in allenvironments (Maisey, 1996). Teleosts, rangingfrom tarpons to tunas, became the most commonpiscivorous open-water predators during theCenozoic. Certain fast-swimming large predatoryteleosts, such as swordfish, seemingly filled a partof the fast-swimming piscivorous predator guildheld by ichthyosaurs and primitive teleosts (e.g.Xiphactinus) during much of the Mesozoic.Ray-finned teleosts with molluscivorous habitsoriginated and diversified in the Eocene, a few othergroups in the Oligocene and Miocene (Vermeij,1987). Additionally, a major evolutionary radiationoccurred in the tropical reef fish fauna of the Eocene.Most of the fossil record of reef fish comes fromLate Cretaceous to Miocene Tethyan reef depositsof southern Europe (Rosen, 1988; Choate andBellwood, 1991). The best reef fish fossils, however,are from the Eocene of Monte Bolca, Italy (Blotte,1980; Choate and Bellwood, 1991; Bellwood, 1996).These fossils are excellently preserved—some retainpigmentation—and represent mass mortality events,probably related to poisonous algal blooms (Choateand Bellwood, 1991).160