Well, that’s a great question – and one that paleontologists had been asking themselves since the animals were first described 175 years ago. A new [study] answered this question.
Paleontologists first thought that hyoliths were molluscs (snails, slugs, clams, oysters, scallops, limpets, squids, octopus, cuttlefish, nautilus and more).
The reason paleontologists thought that hyoliths were molluscs is because of their cone-shaped shell, operculum (a cover for the shell opening), and because of the shape of their larvae. Hyoliths first appear in the Cambrian (541 million years ago) and lived throughout the Paleozoic (541-252 million years ago).
After examining 1500 specimens and looking at the soft tissue preserved in 254 of those specimens, the authors discovered that hyoliths actually contain a lophophore (a frilly feeding structure) and are more closely related to brachiopods.
This study highlights the need to continue to find and collect specimens, even if there are some already in other collections. It also shows us that with enough time, many scientific mysteries can be solved.