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PALEONTOLOGICAL SOCIETY PAPERS, V. 8, 2002polychaete annelids, and scavengers on deadpolychaetes, fish, and squid (Vannier et al., 1998).They have serrated appendages that act like knives(or sandpaper) to abrade their food. Based on theirfeeding appendages, the Early Triassic cypridinids(and possibly the Late Ordovician myodocopids)may have been predators or scavengers oncephalopod carcasses (Vannier et al., 1998).Chondricthyes.—The long-lived hybodontidsflourished in the Triassic and became the dominantJurassic sharks (Maisey, 1982). Hybodontspossessed varied dentition, ranging from highcuspedimpaling teeth to low-crowned crushers,indicating rather generalized predatory diets(Maisey, 1982); they gave rise to swimming,piscivorous sharks, as well as pavement-toothedforms. The hybodont sharks may have arisen inthe Devonian, but they underwent strong adaptiveradiation during the Triassic (Maisey, 1982).Sauropterygian clade.—The sauropterygianclade (Figs. 2, 6; Table 2) contains the Triassic stemgroups such as placodonts, pachypleurosaurs,nothosaurs, and pistosaurs, and the Jurassic-Cretaceous crown groups known as plesiosaurs,pliosaurs, and elasmosaurs (Rieppel, 1999). Verylittle is known about the feeding mechanics ofTriassic stem-group sauropterygians, whichsecondarily became aquatic from their terrestrialancestors (see Rieppel, 2002). Feeding underwater,as the stem-group sauropterygians did, required asuite of anatomical and behavioral adjustments thathad to allow for their adaptive radiation into earlyMesozoic seas (Rieppel, 2002). Suction feedingappears to be the most efficient hydrodyamic wayto solve the underwater feeding dilemma (Lauder,1985); however, “quick snapping bites” at the airwaterinterface (or underwater) are also used,especially by crocodilians (Rieppel, 2002). Triassicsauropterygians covered all styles of feeding, andthus have little overlap in hypothesized feedingstrategies. The varied nearshore habitats in theMiddle Triassic, with lagoonal basins interspersedamong reef habitats, may have accounted for thetrophic-functional diversity of stem-groupsauropterygians (Rieppel, 2002).Placodonts.—During the Middle Triassic, theplacodonts (Figs. 1, 2.1–2.3) evolved fromunknown diapsid reptilian ancestors (Benton, 1993,1997). The Triassic placodonts, sister group to allother Sauropterygia, have members that areinterpreted to have been benthic predators on hardshelledinvertebrate prey. Placodus, for example,had pachyostosis (complete covering of the cheekby dermal bone), which added weight to the jawand thus may have functioned as an adaptation fordurophagy (Rieppel, 2002). Additionally, theprocumbent and chisel-shaped premaxillary anddentary teeth may have functioned to pick offinvertebrates from their substrate, which were thencrushed with the posterior tooth plates before theywere swallowed (Westphal, 1988). Biomechanically,the tooth plates of Placodus were positioned in sucha way as to enhance crushing, but not increase loadto the jaw (Rieppel, 2002). The basal stock ofPlacodus already had large crushing tooth platesand procumbent premaxillary teeth (Rieppel, 2002),indicating that durophagy was an ancestral conditionin this group. The few durophagous taxa ofplacodonts may have had an impact on therediversifying molluscan communities of theTriassic, but they became extinct in the major crisestoward the end of that period.Not all placodonts had dentition indicating thatthey ate benthic hard-shelled prey. More derivedcyamodontids (Placochelys and Psephoderma) lackpremaxillary and anterior dentary teeth, and mayhave picked up benthic soft-substrate invertebrates(like crustaceans) through suction action (Rieppel,2002). Another basal cyamodontoid, Henodus, hasmuch reduced crushing dentition, and may have hadbaleen that was used in sieving benthic invertebrates.Henodus is thus interpreted to have been a bottomfeeder—perhapsan herbivore or omnivore—but itwas not durophagous (Rieppel, 2002).Pachypleurosauria.—Pachypleurosaurs(Fig. 2.7) were swimming reptiles with long headsand interlocking lower and upper sharp teethpresumably for the capture of fish (Benton, 1997).Pachypleurosauria are considered to be the sistergroup of the Nothosauroidea, or the sister taxon toall other Eusauropterygia (composed of nothosaursand plesiosaurs; Rieppel, 2002). Pachypleurosauria124