View - Kowalewski, M. - Virginia Tech

PALEONTOLOGICAL SOCIETY PAPERS, V. 8, 2002assemblages (Taylor et al., 1980; Kitchell et al.,1981; Kitchell, 1986; Kelley, 1988; Kabat, 1990;Anderson et al., 1991; Kelley and Hansen, 2001;see below). The naticid subfamily Polinicinaediversified greatly in the Cenozoic, and thepolinicid body fossil and predatory trace fossilrecord is extensive, especially after the Oligocene(Sohl, 1969; Taylor et al., 1983).The Nassariids (Neogastropods) are carnivoresor scavengers, and until recently, their predatorydrilling habits were in question (Kabat, 1990;Kowalewski, 1993). Kabat (1990), in fact,suggested that drilling did not occur in this group,although the possibility of nassariid drilling wasmentioned by Fischer (1963). Recently, Mortonand Chan (1997) have shown unequivocally thatsome nassarids can drill prey. A few (8 of 30individuals) laboratory-reared juveniles ofNassarius festivus were found with stereotypicallysitedboreholes on the ventral surface of their mainbody whorl (Morton and Chan, 1997, their fig. 1).The boreholes varied in morphology, fromelongate, irregular drillholes to sphericalcountersunk borings that were clearly rasped withthe radula and aided by chemical dissolution. It isthought that drilling may be a juvenile behaviorthat is lost in the adults, as no adult nassariids haveunequivocally been found to drill prey.To date, two species (Austroginella johnsoniand Austroginella muscaria) of marginellidgastropods from southeastern Australia are knownto drill into molluscan prey (Ponder and Taylor,1992). Parabolic in sectional shape and circular tosubcircular in outline, the studied drillholes rangein length from 1.13 mm to 3.1 mm. Additionally,marginellid drillholes are countersunk with a verysmall inner diameter relative to the outer diameter.This inner opening may have an irregular shapethat can be used to distinguish these borings fromthose of other predatory gastropods such asnaticids. Naticids make larger drillholes (seeKowalewski, 1993). However, marginelliddrillholes are similar to octopus drillings (Ponderand Taylor, 1992), and thus may be difficult todistinguish in the fossil record. Like octopods,marginellids may only use the drillhole for injectingtoxins to relax the prey, rather than feeding throughthe hole. Under SEM, the calcareous microstructureis seen to be greatly etched, suggesting a dominantsolutional mechanism for drilling.Cephalopods.—Shell-crushing and crustaceancrushingnautiloids diversified after theCretaceous-Tertiary extinction, and remainedrelatively abundant into the Miocene, whennautiloids were quite diverse and abundant incontinental shelf habitats across the globe (Ward,1987). The earliest Nautilus is known from theEocene–early Oligocene, but no fossils are knownfrom the upper Oligocene to Pleistocene (Teichertand Matsumoto, 1987). In modern seas, nautiloidsextend from Fiji in the east to the Indian Ocean inthe west, and from New Caledonia to Japan (Ward,1987). Natiloids forage for prey or crustacean moltsacross great depth ranges. There may be up to sevenspecies of nautiloids in modern oceans, but severalof the species designations are debated (Saundersand Ward, 1987; Ward, 1987).The prey of Nautilus is seemingly quite differentfrom that of the Mesozoic ammonoids.Unfortunately, the feeding ecology of Nautilus ispoorly known, but it is thought to be both a predatorand a scavenger (Ward, 1987). While directobservations of predation are lacking, evidence fromcrop dissections suggests that nautiloids eatcrustaceans, especially crabs (Saunders and Ward,1987; Ward, 1987; Nixon, 1988). The crop ofNautilus macromphalus, for example, has often beenfound to contain many hermit crabs of one species(Ward, 1987). However, this dietary finding maybe biased in that nearly all Nautilus studied arecaught in traps, which also attract crustaceans.Additionally, nautiloids have been directly observedby divers to eat molts from lobsters and slipperlobsters. With their large, chitinous jaws tipped withcalcium carbonate, nautiloids shred their prey orscavenged items into very small pieces of about 5mm 3 (Nixon, 1988). Predators of Nautilus includesharks, triggerfish, humans, octopods, and perhapsother nautiloids (Ward, 1987).Ammonites and nearly all belemnoids becameextinct during the Cretaceous-Tertiary crisis.However, other coleoid cephalopods, such as the156