Phyllocerida

Phyllocerida is an extinct superfamily of ammonites, a group of extinct marine cephalopod molluscs. They lived during the Jurassic period, from the Lower Jurassic to the Upper Jurassic epochs. Phyllocerida are characterized by their generally smooth, involute shells, meaning that the inner whorls are almost entirely covered by the outer whorls. Their sutures, the lines where the shell septa meet the shell wall, are typically complex and highly frilled or dendritic.

This superfamilly is divided into several families, with the Phylloceratidae being the most prominent and widespread. Phyllocerids are found in marine deposits worldwide, indicating a wide geographical distribution and likely a significant role in ancient marine ecosystems. Their presence in the fossil record is often used for biostratigraphic dating of Jurassic rock formations. The precise evolutionary relationships of Phyllocerida and their origins are subjects of ongoing paleontological research, but they are generally considered to be an early offshoot within the ammonite lineage. Their morphology suggests adaptations for a pelagic lifestyle.