View - Kowalewski, M. - Virginia Tech

PALEONTOLOGICAL SOCIETY PAPERS, V. 8, 2002examined these data in the light of Allmon’s (1996)careful evolutionary studies of these gastropods,but lineage-specific and genus-specific patternsstill do not emerge.Increases in the frequency of shell repair havealso been noted for several ammonoid lineages incomparisons of Early Jurassic (Toarcian) and MiddleJurassic (Callovian) samples from Europe (Kröger,2000) and for environmentally similar samples ofpycnodontine and exogyrine oysters duringsuccessive intervals of the Late Cretaceous in NewJersey (Dietl et al., 2000). Late Cretaceousammonoids generally have higher incidences ofrepair than their older counterparts (Landman andWaage, 1986; Monks, 2000). Many more suchstudies are needed to assess the history of shell repair.Adaptive trends in prey are observable bothwithin clades and in successive replacements ofclades in specified environments. Apertural typesthat limit entry by predators have evolved multipletimes in gastropods, mainly from the late Mesozoiconward, and species with such apertures account forincreasing proportions of the gastropod fauna inwarm-water marine assemblages through time(Vermeij, 1987). Brachiopods with spines and shellreinforcingfolds (plicae) become increasinglyfrequent in assemblages from the Early Devonianto the end of the Paleozoic (Signor and Brett, 1984;Alexander, 1986, 1990). Antipredatory adaptationsin bivalves—crenulated or scalloped valve edges,thickened valve margins, overlapping valves,cementation of one valve to the substratum, spinesand other high-relief sculpture, and external andinternal organic shell layers—have repeatedlyevolved and become more frequent, especially inthe Mesozoic and Cenozoic (Vermeij, 1987; Harper,1991; Harper and Skelton, 1993a, 1993b; Stone,1998). Among ammonoid cephalopods (EarlyDevonian to end-Cretaceous), increases insculptural relief and in the complexity of thejunction between internal septa and the outer shellwall affect many lineages, and imply increasingresistance to shell-crushing predators (Ward, 1986;Daniel et al., 1997; Saunders et al., 1999).Increasing thickness and rugosity, decreasingnumber, and more complex articulation of barnacleplates indicate post-Eocene escalation in manylineages with drilling and test-breaking predators(Palmer, 1982; Zullo, 1984).Traits associated with high locomotorperformance have also increased in frequency andexpression in most mobile groups through time.Rapidly burrowing molluscs appeared mainly inthe Late Cretaceous and Cenozoic (Vermeij, 1987).Chamberlain (1991) has documented generalincreases in speed of swimming amongcephalopods throughout their long (Late Cambrianto Recent) history (see also Ward, 1986).These changes are paralleled by increases in theinferred biting strength and specialization of skeletonbreakingmarine predators. Morphologicallyspecialized shell-breakers with flattened crushingsurfaces in jaws and claws are known from the EarlyDevonian onward. Earliest to appear were pterygotideurypterids, dipnoan lungfish, and various blunttoothedelasmobranchs. Decapod and stomatopodcrustaceans joined this cadre after the Devonian, butspecializations for crushing or cutting shells aremainly post-Cretaceous inventions. Cephalopods,which have a Late Cambrian origin, may have beenshell-breakers as early as the Ordovician, but knowncrushing jaws occur mainly in the Jurassic andCretaceous (summary in Vermeij, 1987). Hybodontsharks may have been the only shell-crushingpredators of the Early Triassic, immediatelyfollowing the end-Permian disaster (Tintori, 1998).A substantial diversification of potentiallymolluscivorous actinopterygian teleost fish beganin the Norian stage of the Late Triassic, followed bythe spectacular diversification of acanthopterygianfish from the Late Cretaceous onward (Tintori, 1998;Wainwright and Bellwood, in press). Marinetetrapods capable of breaking external skeletonsappeared (as placodont reptiles) in the MiddleTriassic, and have been represented by variousreplacing clades ever since.Predators inserting part or all of their bodiesto force entry into external skeletons withoutdrilling or breakage may extend back to the LateOrdovician, when the seastar Promopalaeasterevidently was able forcibly to insert its stomachinto bivalved prey (Blake and Guensburg, 1994).386