THE ROLE OF PREDATORS IN THE PALEOECOLOGY OF COLD METHANE SEEPS IN THE LATE CRETACEOUS PIERRE SEAWAY, SOUTH DAKOTA

Cold methane seeps in the Late Cretaceous Pierre Seaway of North America were safe havens providing pockets of life in otherwise inhospitable settings. Many seeps host low diversity, high density faunas, where ammonites are among the dominant constituents. Other faunal components include gastropods, bivalves, sponges, corals, echinoids, crinoids, and fish. Samples of well-preserved ammonite shell exhibit low δ¹³C values, indicating that the ammonites resided near the vent fluids. Additionally, many ammonite specimens display evidence of lethal and sublethal injuries, mainly inflicted by durophagous predation. We hypothesize that the presence of these injuries is evidence of predation at the seeps. We examined ammonites from 12 seep deposits in the Campanian Pierre Shale of South Dakota and recorded the incidence of predation including sublethal injuries in the form of repair scars, and lethal injuries in the form of bore holes and shell breakage of the body chamber. Of 220 ammonite specimens we examined, we observed 10 possible sublethal injuries and 53 possible lethal injuries. The presence of such injuries indicates that ammonites formed an integral part of an interdependent seep ecosystem.