Behold the hyolith — a bizarre Cambrian-period creature that dwelt on the ocean floor alongside other armored invertebrates like trilobites more than 500 million years ago. Its body was encased in a pair of shells that resembled an ice cream cone with a lid like a trap door. Two tusklike spines protruded from the soft tissue near the hinge, and on top of its mouth was a row of fluttering tentacles.
For 280 million years, strange shelled animals called hyoliths lived on ocean floors around the world. They were one of the many forms of life that appeared during the Cambrian period (543 million to 490 million years ago), when the planet suddenly exploded with all sorts of new — and often odd — species.
Newly discovered fossilized hyoliths that preserve 508-million-year-old soft tissues from these animals reveal that they were part of a group called the Lophophorata, researchers report Jan. 11 in the journal Nature. Animals in this group are distinguished by the tentacles around their mouths.
Hyoliths were only about 0.4 inches (1 centimeter) long. They had cone-shaped shells, topped with a shorter, rounder top shell that made them look like ice cream cones with lids. Wait, make that ice cream cones with lids and stilts — odd curved structures, called helens, protruded out between the hyolith’s two shells and extended below them like a pair of curved arms. These helens seemed to prop the hyoliths off the seafloor slightly.
The effect was an animal that looked something like a very weird clam, and many researchers thought that hyoliths might, like clams, be mollusks. Others classified them as Incertae sedis, which is more or less Latin for “We don’t know.”
“The problem is, for the 175 years since they [the hyoliths]were first described, scientists have had little idea of where these organisms actually fit in the tree of life,” said Joseph Moysiuk, an invertebrate paleontologist at the University of Toronto.
But unlike scientists before them, Moysiuk and his colleagues had more than 1,500 specimens of hyoliths from the Burgess Shale in the Canadian Rockies and the Spence Shale in Idaho and Utah. Of those specimens, 254 had soft tissue preserved.