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PALEONTOLOGICAL SOCIETY PAPERS, V. 8, 2002hard- and soft-shelled invertebrates in the pelagicrealm (Rieppel, 1998). Teeth of some nothosaurs,such as Simosaurus, have a bulbous shape whichmay have had a somewhat durophagous function(Rieppel, 2002). Anatomical evidence indicatesthat Simosaurus had strong neck muscles and wascapable of rapid jaw opening; suction also mayhave been used to round up shelled ammonoids orfish (Rieppel, 2002). Nothosaurus mirabilis hadspecialized jaw adductor muscles, heterodontdentition with procumbent fangs, and a very narrowand elongate skull (Rieppel, 2002). The heterodontdentition suggests most nothosaurs ate fish, althoughthe gastric contents of one nothosaurid (Lariosaurus)contained placodonts and small pachypleurosaurs(Sander, 1989; Tschanz, 1989; Rieppel, 2002). Theymay also have eaten soft-bodied invertebrates, suchas cephalopods. Simosaurus may have eaten hardshelledprey (Rieppel, 2002). Some nothosaurs,because of their large size, may have been at the topof the food chain.Pistosauroidea.—The Triassic Pistosaruoideagave rise to the plesiosaurs that were common inthe Jurassic and Cretaceous seas. Some pistosaurianshad jaws similar to those of the putatively fish-eatingnothosaurids (e.g., Nothosaurus), and others, suchas Pistosaurus, had narrow and elongated pincertypejaws, that had less numerous and widely-spacedheterodont dentition with maxillary fangs (Rieppel,2002). Puncturing prey, rather than suction feeding,may have been the modus operandi of thesecreatures, and they may have fed on soft-shelledpelagic invertebrates and fish (Rieppel, 2002).Ichthyosauria.—Ichthyosaurs (Order Ichthyosauria)(Figs. 2.4–2.6; 4) are known from the LowerTriassic to Cenomanian (Bardet, 1994), but theyhave only recently been studied in detail (Callaway,1997a). Triassic ichthyosaurs were nearly as diverseand widespread as Jurassic ichthyosaurs, but arenotoriously affected by preservational bias(Callaway, 1997b; Sander, 1997). Because of thispreservational bias, little is known about theevolution of dentition in Triassic ichthyosaurs. Mostof them likely had heterodont dentition, indicatingthat they were generalist feeders in nearshore waters(Massare and Calloway, 1990).Some Middle Triassic ichthyosaurs with largerear teeth may have been molluscivorous (Massareand Callaway, 1990). In the Jurassic and Cretaceous,the dentition became homodont, indicating that theymay have become specialized on pelagic prey(Massare and Callaway, 1990). Perhaps they werespecialists on fish and/or soft-bodied cephalopods(Sander, 1997; Massare and Callaway, 1990).Gastric contents indicate that they may have fed onbelemnite cephalopods, although no belemnite orammonoid shells have ever been found inichthyosaurian stomach contents. Based on bodyform, by the end of the Triassic, ichthyosaurs werehydrodynamically advanced and were very fastswimminganimals (Lingham-Soliar, 2001).Pterosaurs.—The appearance of pterosaurs inthe middle of the Triassic Period (Benton, 1993) mayhave increased predation pressure on near-surfacenektonic organisms, including fish and cephalopods.The long jaws and impaling spike-like teeth ofrhamphorhynchids and many pterosauroids suggestsa piscivorous diet in these flying reptiles.TRIASSIC BENTHICORGANISMS:ANTIPREDATORY RESPONSES?Varied morphological and behavioral featuresof benthic invertebrates have been interpreted asantipredatory adaptations (Fig. 3), although manyof these features may be merely exaptations(sensu Gould and Vrba, 1982). Triassic benthicfaunas are decidedly “no frills” relative to thoseof the late Paleozoic (Valentine, 1973). Shells arerelatively thin and mainly lacking in spines. Inaddition, several groups of cemented bivalves—the ostreids, gryphaeids, plicatulids, andterquemids—first became abundant on hardsubstrates in the Triassic. Harper (1991) hasdemonstrated experimentally that predators avoidcemented bivalves when given a choice.The evolutionary breakthrough of mantlefusion in bivalves led to the rapid development ofinfaunal clades in the early Mesozoic (Stanley,1977). Mud- and rock-boring bivalves also firstbecame common during this time (Seilacher, 1985;128