'Living Fossil' Thought Extinct For 273 Million Years Found Thriving on Ocean Floor

A symbiotic relationship between two marine lifeforms has just been discovered thriving at the bottom of the ocean, after disappearing from the fossil record for hundreds of millions of years.

Scientists have found non-skeletal corals growing from the stalks of marine animals known as crinoids, or sea lilies, on the floor of the Pacific Ocean, off the coasts of Honshu and Shikoku in Japan.

"These specimens represent the first detailed records and examinations of a recent syn vivo association of a crinoid (host) and a hexacoral (epibiont)," the researchers wrote in their paper, "and therefore analyses of these associations can shed new light on our understanding of these common Paleozoic associations."

During the Paleozoic era, crinoids and corals seem to have gotten along very well indeed. The seafloor fossil record is full of it, yielding countless examples of corals overgrowing crinoid stems to climb above the seafloor into the water column, to stronger ocean currents for filter-feeding.

Yet these benthic besties disappeared from the fossil record around 273 million years ago, after the specific crinoids and corals in question went extinct. Other species of crinoids and corals emerged in the Mesozoic, following the Permian-Triassic extinction - but never again have we seen them together in a symbiotic relationship. Read the free article.