Pinhead-sized sea creature was a bag with a mouth

Anus may have been absent in odd new fossils from 540 million years ago

deuterostome fossil

MOUTHING OFF  New fossils show tiny creatures with accordion mouths (one shown) that lived 540 million years ago. The animals are the earliest known deuterostomes, a category so big it includes everything from humans to starfish.

J. Han et al/ Nature 2017

A roughly 540-million-year-old creature that may have once skimmed shorelines was a real oddball.

Dozens of peculiar, roundish fossils discovered in what is now South China represent the earliest known deuterostomes, a gigantic category of creatures that includes everything from humans to sea cucumbers.

No bigger than a pinhead, the fossils have wrinkly, baglike bodies and gaping mouths that are pleated around the edges like an accordion, researchers report January 30 in Nature. Unlike most other deuterostomes, the animals don’t seem to have an anus. Instead, the ancient oddities, named Saccorhytus coronarius, may have leaked waste (and other bodily fluids like mucus and sex cells) out of tiny holes lining their sides. These holes may have later evolved into gill slits.

A tough, flexible skin would have protected Saccorhytus as it wriggled through grains of dirt, the authors suggest. The find supports previous suggestions that the earliest deuterostomes were actually a kind of water-dwelling worm.

Meghan Rosen is a staff writer who reports on the life sciences for Science News. She earned a Ph.D. in biochemistry and molecular biology with an emphasis in biotechnology from the University of California, Davis, and later graduated from the science communication program at UC Santa Cruz.

More Stories from Science News on Paleontology

From the Nature Index

Paid Content