Phylloceratidae

Phylloceratidae is an extinct family of ammonites, a group of marine mollusks belonging to the subclass Ammonoidea. These ammonites are characterized by their smooth, evolute shells, meaning the whorls of the shell are largely or entirely exposed. The suture lines, which are the complex patterns where the septa (internal walls) meet the shell, are typically phylloceratid in form, featuring broad, rounded lobes and saddles. This family first appeared in the Triassic period and persisted through the Jurassic and Cretaceous periods. They are considered to be among the most phylogenetically primitive of the Ammonitida, and their lineage is thought to be ancestral to many other ammonite groups. Phylloceratids are often found in marine sedimentary rocks worldwide and are important index fossils for dating these rock layers. Their distribution suggests they inhabited relatively warm, shallow marine environments. The exact ecological role and life cycle of Phylloceratidae are still subjects of scientific research, but their presence indicates a significant component of Mesozoic marine ecosystems.