Sea lilies driven by competition from predators

Posted By Ian Randall on 18 March 2010

Sea urchins have been dining off of crinoids for over 200 million years, forcing some crinoids – the sea lilies – to evolve the means to flee across the sea floor to safety, new research has shown. The study, led by the University of Michigan, is being published online in this week’s Proceedings of the National Academy of Sciences.

Sea lilies were long thought to be as sedate as the garden flowers they so resemble, but Tomasz Baumiller, a palaeontologist at the University of Michigan, and his colleagues have presented footage which shows sea lilies ditching the ends of their stalks and creeping around on their feathered arms. It would seem that this motion is often to escape attacking sea urchins – these creatures prey on live sea lilies, tearing off arms for food when given the chance.

Baumiller and his team looked at the behaviour of sea urchins by placing live specimens in a tank with both live crinoids and parts of dead ones. All of the urchins were seen to take up the chance to eat off of the crinoids – leaving characteristic ‘bite’ marks on the indigestible crinoid remains that they passed through them.

When they examined the fossil record in Poland, similar markings could also be seen in a notable proportion of crinoid stalk fossils – the specimens studied dated back to the Triassic Period, 225 million years ago.

Sea Urchins. Photo credit - Mbz1

The researchers believe that the crinoids evolved this ability to move as a direct response to their interaction with predators.

This is not uncommon in species bound by the ties of a predatory relationship, but it is unusual to see such a development this early. The most notable shift in predator/prey diversities came in the Mesozoic Marine Revolution, 150 million years ago – but in the case of sea lilies, Baumiller and his team believes the battle to survive began much earlier.


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