View - Kowalewski, M. - Virginia Tech

PALEONTOLOGICAL SOCIETY PAPERS, V. 8, 2002their morphology has remained relatively the samesince their origin in the Ordovician (Aronson,1991). It is possible that they developed betterautotomization of their arms, like some crinoids;or maybe they developed into distasteful prey(Aronson, 1991). The evolutionary radiation of thespatangoids (and holasteroids) in the Cretaceousmay have been the result of the Jurassic innovationof pencillate tube feet, a feature shared with noother echinoid group (Simms, 1990). EarlyCretaceous spatangoids (Hemiaster eleganswashitae) are reported to have drillholes fromparasitic gastropods (Kier, 1981). Parasitic drillingsare commonly associated with deformation of theechinoid ossicles where the parasite housed itself.Fish bite marks are well preserved on completeasterioids and asteroid ossicles from the LateCretaceous White Chalk of northwestern Germany(Neumann, 2000). On some specimens, serratedtooth marks may be related to galeoid sharkpredation. Regurgitate pellets are also common inthe White Chalk, and indicate that predation bythese durophagous fish may have been sizeselective (Neumann, 2000).Vertebrates.—As with late Paleozoic fish,armor does not appear to have been a significantpart of the response to escalation among Mesozoicmarine vertebrates. With the exception of relativelyslow-moving placodonts and marine turtles, noneof the marine vertebrates developed any unusualarmor during the Mesozoic. Indeed, withinactinopterygian fish there is a distinct trend towardreduction of ganoid scales in favor of lighter andless protective cycloid and ctenoid types (Patterson,1994; Benton, 1997). Presumably, this scalereduction reflects the ineffectiveness of dermalarmor against large predators, which demonstrablyswallowed prey whole (Voihl, 1990). This furtherreduction in armament is clearly coordinated withthe development of improved swimming speed,buoyancy control, and maneuverability in theCretaceous teleosts. In turn, this increased mobilitymay well have triggered adaptations for improvedspeed, maneuverability, and/or stealth among largerpredators, such as the neoselachian sharks,plesiosaurs, ichthyosaurs, and mosasaurs.CENOZOIC PREDATORSThe Cretaceous-Tertiary extinction had adevasting impact on pelagic ecosystems. Ammonitesand belemnoids, as well as large vertebrate predators,were decimated by this event. All of the marinereptilian predator guilds, except sea snakes and seaturtles, became extinct during this crisis—includingmosasaurs, plesiosaurs, and ichthyosaurs, in additionto the flying pterosaurs. This left only the highlysuccessful neoselachian sharks and teleost fishes inthe vertebrate predator realm. Marine mammalsemerged in the Eocene to essentially take over theecological void left by Mesozoic marine reptiles(Table 4). In fact, tooth dentition in marine mammalsclosely parallels that of the Mesozoic marine reptiles(Massare, 1987, 1997).Conversely, many benthic invertebratepredators, such as naticid and muricid gastropodsand various decapod crustaceans, were seeminglylittle affected by the terminal Cretaceous extinctions.Several groups of shell-drilling predators evolvedor diversified within the Cenozoic (for review, seeVermeij, 1987); some groups, such as theneogastropods, evolved in the Late Cretaceous.Prosobranch gastropod predators, the dominantdrillers, were much more common in the Cenozoicthan at any other time, though the Mesozoic recordneeds to be more throughly examined (Kowalewskiet al., 1998). The record of octopod shell drilling ischiefly Cenozoic, with the soft-bodied octopodfossil record primarily within the Cretaceous toPaleogene (Engeser 1988; Harper, 2002).Several major groups of vertebrate shellcrushingand shucking predators that may haveseriously impacted benthic and pelagic marinebiotas evolved or diversified during the Cenozoic:shell-crushing sea turtles (i.e., the single genusCaretta), the coral reef teleost fishes and otherteleosts, rays and skates, diving marine and shorebirds, pinnipeds, sea otters, gray whales, andhumans. Among mammals, the origination ofpinnipeds (seals and walruses), the cetaceans(especially the gray whale) in the Eocene, and seaotters (Carnivora; Family Mustelidae) in the lateMiocene also potentially impacted Cenozoic152