phylloceratoid

Phylloceratoid is an extinct superfamily of ammonites, a group of marine cephalopod molluscs belonging to the subclass Ammonoidea. These ammonites are characterized by their coiled shells, which are typically evolute, meaning that the whorls are largely exposed. The shell ornamentation of phylloceratoids is generally smooth, with only faint growth lines or subtle ribbing. Their suture lines, the complex patterns where the shell septa meet the inner shell wall, are particularly distinctive. Phylloceratoid sutures are highly complex and highly folded, often described as "ceratitic" or "goniatitic" in their degree of complexity, though they are more specifically classified as phylloceratoid in their advanced complexity.

Phylloceratoids first appeared in the Triassic period and persisted through the Jurassic and Cretaceous periods, becoming extinct at the end of the Cretaceous along with all other non-avian dinosaurs and ammonites. They were a widespread and diverse group, found in marine deposits throughout the world. Their fossils are important index fossils for dating rock strata from the Mesozoic Era. The superfamily is divided into several families, including the Phylloceratidae, Gaudryceratidae, and Tetragonitidae. The precise evolutionary relationships within the Phylloceratoidae are still a subject of ongoing research.