Endocerid
| Endocerida Temporal range: Floian–Hirnantian |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Cephalopoda |
| Subclass: | Nautiloidea |
| Order: |
Endocerida Teichert, 1933 |
| families | |
† Proterocameroceratidae
† Piloceratidae
† Endoceratidae
Endocerida is an extinct nautiloid order, a group of cephalopods from the Lower Paleozoic with cone-like deposits in its siphuncle.
Endocerida comprises a diverse group of cephalopods that lived from the Early Ordovician possibly to the Late Silurian. Their shells varied in form. Some were straight (orthoconic) others curved (cyrtoconic); some were long (longiconic), others short (breviconic). Some long-shelled forms like Endoceras attained lengths as much as 3.5 metres (11 ft). The related Cameroceras is anecdotally reported to have reached lengths approaching 9 metres (30 ft), but these claims are not unproblematic (Teichert and Kümmel 1960). The overwhelming majority of endocerids and nautiloids in general are much smaller, usually less than a meter long fully grown.
Endocerids may have had a relatively small body chamber as well as a proportionally large siphuncle that in some reached nearly half the shell diameter, suggesting much of the visceral mass may have been housed within the siphuncle itself rather than just in the body chamber as with other nautiloids (Teichert, 1964). Endocerids are primarily distinguished by the presence of calcareous deposits, known as endocones, formed in the more apical portion of the siphuncle and thought to counterweight the animal’s body. The chambers (camerae) of endocerids are always free of organic deposits, unlike other orders such as the Michelinocerida and Actinocerida.
Endocerids may have been the superpredators of the Ordovician, probably living close to the sea floor, and preying on trilobites, molluscs, brachiopods and other bottom-dwelling organisms. They were probably not active nektonic swimmers, but rather crawled over the floor of epicontinental seas or lay there in ambush. They probably filled a different ecological niche than that filled by such as sharks and squid today.
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