|-Marine mollusc with straight, curved or coiled shell.
-Soft bodied "foot" is modified to ring of tentacles around mouth.
-Shell is composed mostly of aragonite and is filed with gas to govern buoyancy.
-Group evolved from the Nautiloidea in Silurian times with an increase in complexity of the suture line, and migration of the siphuncle to the outer margin of the shell.
-Represented by three orders: the Goniatitida, Prolecanitida and Cerititida.
|-Goniatitida were the bulk of Permian ammonoids, but were suffering decline throughout the Permian.
-Suffered abupt extinction of remaining genera at P-T boundary.
-One goniatite genus seen in basal Triassic which dies out very quickly.
-Prolecanitida were small order which was declining throughout Permian.
-Cerititida evolved and diversified from the Prolecanitida as they were declining in the Late Permian.