View - Kowalewski, M. - Virginia Tech

WALKER AND BRETT—POST-PALEOZOIC PATTERNS IN MARINE PREDATIONcool climate may lead to thicker prismatic outer shelllayers in some cardiid bivalves, similar to those ofvenerid bivalves (Schneider and Carter, 2001).Cardiid bivalves are known for their spines.Cardiid spines can be formed in different ways: 1)by a mantle that is strongly reflected over exteriorshell surfaces; 2) by extensions of the normal outer,or outer and middle shell layers; or 3) by theperiostracum (formed on the undersurface of theperiostracum, and cemented to the shell exterior).Cemented periostracal granules or spines inCarboniferous astartids, and in three subfamiliesof cardiids (i.e., colpomyid and mytilidpteriomorhians and trigonioid palaeoheterodonts),suggest that periostracal mineralizing isplesiomorphic for the bivalvia, and is merelyretained by many anomalodesmatans (Schneiderand Carter, 2001). Thus, some spine forms in theseMesozoic and Cenozoic groups may be partly orlargely the result of phylogenetic and physicalenvironmental contraints.Ammonoids as Prey.—Ammonoids are knownto have sublethal injuries from the Mesozoic thatmay not have affected their bouyancy as much assublethal injuries in nautiloids (Kröger, 2002).Unfortunately, little quantitative data exists forshell repair in ammonoids during this time.Westermann (1996) suggests that ammonoids livedin deeper-water areas to avoid predators, especiallyin the Cretaceous. However, there is now extensiveevidence that marine reptiles were able to dive todeep depths during this time.Vermeij suggests that shell repair increases inammonoids during the Mesozoic, although he makesa plea that more data be accumulated in order toreally assess this claim (Vermeij, 1987, p. 283–284).To date, little if any data exist to analyzeantipredatory features and predation on Mesozoicammonoids. Because shallow-water and deep-waterforms were abundant, and because ammonoidsoccupied many different habitats within thosesettings during the Jurassic and Cretaceous, theywould be ideal organisms by which examineenvironmental records of predation.Ward (1986, p. 818) states that there is“abundant evidence…suggesting that predation byshell-breaking predators commonly occurred, forbreak marks are common in Jurassic and Cretaceousammonites,” but he does not provide data to supportthis statement. Data are needed on the number ofammonoid shells with evidence of healed injuries,and on whether this varies by environment ofdeposition, and on shell ornamentation through theMesozoic. Equally important would be acomparative examination of healed scars onmicroconchs versus macroconchs, and on demersalversus more planktonic forms of ammonoids.A few direct records of predation on ammonoidshave been reported. Several examples of ammonoidswith smaller ammonoid shells in their bodychambers are cited above. Ammonite shell fragmentsare known from fish feces from the SolnhofenLimestone in Germany (Schindewolf, 1958). Anunknown marine reptile apparently left twentypossible bite marks on a specimen of the MiddleJurassic ammonoid Kosmoceras gulielmi from theMiddle Oxford Clay, England (Ward andHollingworth, 1990). The bite marks are surroundedby an inclined ring of fractured shell, and becausethere was no sign of healing, the bites are consideredto have been fatal to the ammonoid (Ward andHollingworth, 1990). It is also thought, because ofthe diversity of predatory marine reptiles, fish, andbelemnites, that ammonoids may have lived indeeper, slightly more oxygen-deficient waters at thistime (Westermann, 1996). Vermeij (1987, p. 283)reviewed the limited anecdotal informationconcerning shell repair on ammonoids and suggestedthat the incidence of shell repair was low in Earlyand Middle Jurassic ammonoids.If benthic durophagous predators were preyingon ammonoids, the ammonoid prey should show atrend in antipredatory ornamentation and shellrepair through the Mesozoic in accordance withthe Mesozoic Marine Revolution theory of Vermeij(1977, 1987). As is the case for the Triassic, littleis known about antipredatory effects of ammonoidshell shape and sculpture, although shell crushingmarine reptiles, fish, and other cephalopods werequite diverse in the Jurassic and Cretaceous.Costae and spines in ammonoids have beenconsidered to be antipredatory (Logan, 1974;149