Phylloceratida

Phylloceratida is an extinct order of cephalopods that lived during the Devonian and Carboniferous periods, approximately 419 to 299 million years ago. They are characterized by their distinctive, leaf-like shells, which are often referred to as "phylloceratoid" shells. These shells are typically flat, oval, or circular in shape, and they are composed of aragonite, a form of calcium carbonate. The internal structure of the shell is complex, with a series of chambers that housed the animal's internal organs.

Phylloceratids are believed to have been active predators, using their tentacles to capture prey. Their shells were likely used for protection and buoyancy, as many cephalopods use their shells for these purposes. The order includes several genera, such as Phylloceras and Phylloceratoides, which are known from fossil records found in Europe, North America, and Asia.

The extinction of phylloceratids is thought to have been caused by a combination of factors, including changes in ocean chemistry, climate change, and competition with other cephalopod groups. Despite their extinction, phylloceratids have left a significant fossil record, providing valuable insights into the evolution of cephalopods and the history of life on Earth.