ANN ARBOR, Mich.---Nature abounds with examples of evolutionary arms races. Certain marine snails, for example, evolved thick shells and spines to avoid be eaten, but crabs and fish foiled the snails by developing shell-crushing claws and jaws.
Common as such interactions may be, it's often difficult to trace their origins back in evolutionary time.
Now, a study by University of Michigan paleontologist Tomasz Baumiller and colleagues finds that sea urchins have been preying on marine animals known as crinoids for more than 200 million years and suggests that such interactions drove one type of crinoid---the sea lily---to develop the ability to escape by creeping along the ocean floor. The work, which builds on previous research on present-day sea lilies and urchins, is scheduled to be published online this week in the Proceedings of the National Academy of Sciences.
With their long stalks and feathery arms, sea lilies look a lot like their garden-variety namesakes. Perhaps because of that resemblance, scientists long had thought that sea lilies stayed rooted instead of moving around like their stalkless relatives, the feather stars. But in the 1980s, Baumiller and collaborator Charles Messing of Nova Southeastern University's Oceanographic Center in Dania Beach, Fla., observed sea lilies shedding the ends of their stalks to release themselves from their anchor points and using their feathery arms to crawl away, dragging their stalks behind them.
Then, while going through hundreds of hours of video shot during submersible dives, the two researchers came across footage that offered an explanation for why sea lilies might get up and go. The videos showed sea urchins lurking in gardens of sea lilies, some of which appeared to be creeping away from the predators. In some photos, the sea floor around the urchins was littered with sea lily arms, like table scraps left from a feast. Further studies by Baumiller, Messing and
|Contact: Nancy Ross-Flanigan|
University of Michigan