Aulococerida

Aulacocerida comprises an order of coleoid cephalopods within the Belemnoidea with a stratigraphic range extending from the Permian to the lower Jurassic.

Description
Shells,the only remaining part, of aulacocerids, like those of other belemnoids, have three parts going from the apex forward: rostrom, phragmocone, and pro-ostracum. The rostrom is a massive structure that provides a counterweight to that of the animal at the opposite end. The phragmocone is the chambered portion, a carryover from the nautiloid (bactratid) ancestors. The pro-ostracom is what's left of the body chamber.

The rostrum in aulococerids is made of aragonite (a variety of calcium carbonate) and is massive with incised grooves. Chambers in the phragmocone are somewhat long, the siphuncle ventral,  and the apical angle narrow. The pro-ostrocum consists of an entire body chamber, retained from the bactratid ancestors. Aulacocerids, when alive, had ten arms, armed with smooth hooks.

Derivation & Descendants
The Aulacocerida, which has its ancestry in the orthocerid Bactritidae, give rise in the very early Jurassic to the Belemnitida whose range extends to the end of the Cretaceous.

Composition
Families within the Aulocerida are the Aulococeratidae, Chitinoteuthididae, Palaeobelemnopsidae, and Xiphoteuthididae