Predation-facilitated preservation of echinoids in a tropical marine environment

Actuopaleontological studies of echinoids and their predators in modern ecosystems can augment our ability to identify and interpret the fossil record of predation. Here, we examine present-day interactions between the spatangoid Meoma ventricosa and the drilling gastropod Cassis tuberosa from a shallow tropical marine habitat (San Salvador Island, Bahamas) to assess the impact of drilling predation on the fossilization potential of echinoids, estimate drilling frequency, characterize drill hole morphology, and evaluate size and site selectivity of predators. Cassids produced recognizable drill holes ranging from 2-14 mm in diameter. A comparison of drilled versus live individuals suggested that predation was size-selective with preference toward smaller prey (p << 0.001), whereas landmark morphometrics revealed no evidence of stereotypy in specific attack site, drill holes were preferentially located on the oral side of the test (85.2%). Although the annual mortality of M. ventricosa attributed to C. tuberosa was 0.021 individuals per m (super 2) , the drilling frequency in samples of dead echinoid tests was 96.8%. This exceedingly high drilling frequency most likely reflects the fact that echinoids killed by C. tuberosa-a predator that immobilizes, drills, kills, and consumes M. ventricosa buried in the sediment-have a greater chance of preservation than echinoids that died due to other causes (e.g., fish predation). These results not only suggest that the frequency of drilled prey specimens may greatly exaggerate the importance of certain species of drilling predators, but also indicate that certain predators may play a critical role in enhancing the fossilization potential of their prey.