Bellerophontida

Bellerophontida is an extinct order of marine gastropod molluscs. They were characterized by a coiled shell, often with a prominent, stepped spire. These creatures inhabited the seas during the Paleozoic Era, from the Cambrian period to the Permian period. Their shells typically displayed strong sculpturing, featuring radial ribs and axial growth lines.

The exact placement of Bellerophontida within Gastropoda has been a subject of debate among paleontologists. Historically, they were often considered a primitive group, but modern phylogenetic analyses suggest a more complex evolutionary history. Some researchers believe they may represent a polyphyletic group, meaning they do not share a single common ancestor. Others place them within the Bellerophontida class, a distinct group from modern Gastropoda.

Fossils of Bellerophontida are found in marine sedimentary rocks worldwide. They are important index fossils, helping geologists to date rock layers from the Paleozoic. Their diet is thought to have consisted of algae or detritus, based on the morphology of their shells and associated fossil evidence. The extinction of Bellerophontida occurred at the end of the Permian period, during the Permian-Triassic extinction event, one of the most severe mass extinctions in Earth's history.