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.

Since its discovery in the 19th century, the hyolith has puzzled paleontologists. Some thought it was a mollusk, like a snail or clam. Others said it belonged to its own group of animals.

Joseph Moysiuk, an undergraduate student at the University of Toronto, thinks he has solved the mystery. After analyzing more than 1,500 hyolith fossils, Mr. Moysiuk has concluded that the hyolith belonged to a known group of organisms called lophophorates, which would make them most closely related to present-day brachiopods.