View - Kowalewski, M. - Virginia Tech

PALEONTOLOGICAL SOCIETY PAPERS, V. 8, 2002Pelagic Predators.—Although pelagicpredation by swimming arthropods or cephalopodsmay have occurred as early as the Cambrian, thefirst direct evidence for predator-prey relationshipsamong nektonic organisms is from the Devonian(Fig. 7). The rise of goniatite ammonoids in theDevonian may have impacted the pelagic ecosystem.These presumably predatory cephalopods arecommomly found in settings in which there is littleor no benthic fauna (e.g., black shales recordinganoxic sea floors). Hence, these organisms may havefed on pelagic organisms, such as swimmingcrustaceans, other cephalopods, conodont animals,and perhaps small fish (Lehmann, 1976, 1988).Many of the arthrodires, with sharp shearinggnathal plates, were undoubtedly piscivorous. Hlavin(1973, 1990) reports on an articulated specimen ofthe arthrodire Holdenius, from the Upper DevonianCleveland Shale, preserved adjacent to the remainsof its prey: a ctenacanth shark, which had been bittenin half (Fig. 8). This is direct evidence forpredation—although failed predation in this case:an anterior dorsal spine from the ctenacanth wasfound lodged in the palate and extending into thebraincase of the Holdenius. The arthrodire wasprobably killed instantly when it was impaled onthe spine of its prey (a lose-lose situation!).Other groups, such as cladodont sharks, withsharp, cusped teeth, clearly had an impact on fishand on certain probably pelagic invertebrate prey.Williams (1990) provides an excellent summaryof evidence for cladodont predation from fecalFIGURE 7—Time-line of appearance of major groups of Paleozoic pelagic predators and prey.104