DRILLING AND CRUSHING PREDATION OF BENTHIC INVERTEBRATES DURING THE LATE TRIASSIC IN TETHYS

Italian marine deposits comprising the argillaceous Riva di Solto (ARS) Formation in northern Italy record a unique alternating depositional regime including a diverse shallow marine benthic fauna in silty carbonates and interbedded shales which contain abundant fossils of vertebrates and arthropods from this basin, including many predatory fishes. Thus, regional patterns of predation can be tracked through much of the Norian Stage of the Late Triassic, a critical interval in the rise of modern-style marine predation. Early Norian benthic taxa are dominated by stationary epifauna, which are replaced by burrowing bivalves by the end of the Norian Stage in the ARS. This transition is marked by a dramatic proliferation of shell-crushing fishes that began to radiate in the late Middle Triassic, and only a single drilled bivalve was observed (in a burrowing clam, <1% of the identified specimens from the ARS). These findings suggest that drilling predation was not an adaptive method in the latest Triassic, while the abundance of shell-crushing predators cruising the sea floor surface may have induced dramatic paleoecological shifts in the benthos that persisted for much of the Mesozoic Era.