Endocerida

The Endocerida comprises an order of nautiloid cephalopods that lived during the early Paleozoic (mainly Ordovician) that grew to be rather large, some as long as 9m (about 30 ft). Most are generally straight or slightly curved. Siphuncles are ventral in position and proportionally large, as much as half the shell diameter. Septal necks range from almost no existant to extending the full length of the chambers, reaching the previous septa.

Derivation is from the Ellesmeroceratidae in the very Early Ordovician through the development of endocones in the posterior part of the siphuncle which brove ballast which helped keep the animal horizonal in addition to adding rigidity. Endocones are nested, or stacked, cone shaped deposits that open forward through which runs a narrow tube, the endosiphotube, which is partitioned by diaphragms, a carry-over from the ellesmerocerids. It is from these endocones that the order gets its name.

Two groups are recognized. In the first the initial part of the shell is taken up entirely by the siphuncle and the sirst septum and chamber are formed one to several centimenters from the apex. In the second the first chamber is formed at the apex and the entire phragmocone is camerate.

Endoceroid Families
The Endocerida includes the following familes.


 * Endoceratidae L-U Ord.-?M Sil.
 * Proterocameroceratidae Predom. L Ord
 * Piloceratidae L Ord
 * Chihilioceratidae L Ord
 * Manchuroceratidae L Ord
 * Thylacoceratidae L Ord
 * Emmonsoceratidae M Ord
 * Padunoceratidae M Ord
 * Narthacoceratidae M -?U Ord
 * Humeroceratidae M Sil

Some like the Endoceratidae, Proterocameroceratidae, and Piloceratidae include numerous genera. Others like Padunoceratidae and Narthacoceratidae, as of 1964 were each represented by a single genus.