Tom Baumiller’s research bridges the gap between ecological and evolutionary time scales: he studies how organisms interact with their physical and biotic environment, and explores the ecological and evolutionary consequences of these interactions. Crinoids are favorite subjects, in part because modern representatives can be studied in situ and in the lab, and the group has a rich and long fossil record.
Documenting biotic interactions has been a major challenge. This is particularly daunting when dealing with fossils, but even interactions in the Recent are often difficult to document. For example, it was only recently that we found today’s sea urchins biting pieces off stalks of live sea lilies. Since sea lilies can shed their stalks and crawl, Baumiller and his colleagues postulated that stalk shedding and crawling evolved as an escape from slow-moving benthic predators.
Sea urchin bite marks are just one sign of predation: drill holes are more common and have been more widely studied. Drill holes in crinoids and blastoids indicate that platyceratids (a group of Paleozoic gastropods) possessed the ability to drill and while they may have also drilled brachiopods and other invertebrates, nevertheless drilling remained a minor strategy in the Paleozoic compared to its subsequent ubiquity. Whether this was due to intrinsic constraints or differences in types of available prey, remains an unanswered.
Injuries to crinoid arms are also an indicator of biotic interactions, but since those regenerate, such injuries are ephemeral. Theoretical treatment indicates that frequency of such injuries records predation pressure, an important parameter for studying the ecological and evolutionary impact of predation. A project in Honduras aims to assess crinoid injuries as a function of depth (450-2000 ft) to test the hypothesis that fish predation drove stalked crinoids from shallower habitats, where they used to thrive in the geologic past.