Fossils provide unprecedented clues to the origins of the starfish
For decades, scientists have sought to understand how the present-day starfish came to be. Newly analyzed fossils should help, as they represent a transitional step between the starfish and the family tree it branched off of.
Unearthed a number of years ago in Morroco's Anti-Atlas mountain range, the fossils are the remains of a creature that has now been named Cantabrigiaster fezouataensis. And while it looks starfish-like, a recent University of Cambridge-led analysis has determined that it actually lacks about 60 percent of a modern starfish's body plan. Instead, it combines features of both a starfish and a sea lily.
Also known as crinoids, sea lilies still exist, and they aren't plants. They're actually animals with a body consisting of a "stem" that's anchored to the seabed, topped with filter-feeding arms which they wave through the water to snag food items such as plankton. Both crinoids and starfish – along with creatures such as brittle stars, sea urchins and sea cucumbers – are members of a spiny-skinned group of animals called echinoderms.
Approximately 480 million years old, the Cantabrigiaster fossils have arms like a starfish, but those arms are covered in feathery filter-feeding appendages like those of a sea lily. Each of those arms also incorporates a starfish-like "food groove" running down the middle of its underside, which is used to funnel food from the end of the arm to the creature's mouth, located at the center of its body.
"One thing we hope to answer in the future is why starfish developed their five arms," says the lead scientist, Dr. Aaron Hunter. "It seems to be a stable shape for them to adopt – but we don't yet know why. We still need to keep searching for the fossil that gives us that particular connection, but by going right back to the early ancestors like Cantabrigiaster we are getting closer to that answer."
A paper on the research was recently published in the journal Biology Letters.
Source: University of Cambridge