Endoceratidae is a family of large to very large straight shelled

nautiloid Nautiloids are a group of marine cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and '' Allonautilus''. Fossil nautiloids are diverse and speciose, with over 2,500 recorded specie ...

cephalopods belonging to the order

Endocerida Endocerida is an extinct nautiloid order, a group of cephalopods from the Lower Paleozoic with cone-like deposits in their siphuncle. Endocerida was a diverse group of cephalopods that lived from the Early Ordovician possibly to the Late Silu ...

that lived during the Middle and Late

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...

. They include the largest known

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

invertebrates, represented by '' Endoceras'' and ''

Cameroceras ''Cameroceras'' ("chambered horn") is a genus of extinct, giant orthoconic cephalopod that lived mainly during the Ordovician period. It first appears during the middle Ordovician, around 470 million years ago, and was a fairly common componen ...

''.Teichert C, (1964). Endoceratoidea; Treatise on Invertebrate Paleontology, ''Part K, Mollusca 3''.Flower R. H. (May 1958). "Some Chazyan and Mohawkian Endoceratida", ''Jour Paleo'' 32 (2) pp 433-458

Description

Endocerids are characterized by large, generally ventral

siphuncles The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and ...

with simple endocones which lack the more complex structures associated with the

Proterocameroceratidae The ''Proterocameroceratidae'' were the first of the Endocerida. They began early in the Ordovician with ''Proendoceras'' or similar genus which had developed endocones, replacing the diaphragms of the ellesmerocerid ancestor. Proterocamerocera ...

and their derivatives. Endocones, nested cone-shaped deposits characteristic of the Endocerida, form in the apical portion of the siphuncle where they balanced the weight of the animal in the body chamber at the opposite end. This helped assure a horizontal orientation while the endoceratid animal was alive. The septal necks are holochoantitic, reaching the previous septum and sometimes beyond, as macrochoantic. Connecting rings, which may be moderately thin, form a lining on the interior of the necks. In some forms, such as '' Nanno'' and '' Chazyoceras'' the siphuncle is swollen at the apex so as to preclude the presence of adjacent camerae. In others, such as ''

'' and '' Vaginoceras'' the siphuncle is tubular with chambers formed adjacently from the very start. The taxonomic significance of either in undetermined, other than as used to define a particular genus.

Origin

The Endoceratidae arose from the upper

Canadian Canadians (french: Canadiens) are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, many (or all) of these connections exist and are collectively the source of ...

(Lower Ordovician) Piloceratidae according to Rousseau Flower,Flower, R.H. 1976. Ordovician Cephalopod Faunas and Their Role in Correlation,proceedings Paleontological Association. which have similar simple structured siphuncles, although they may resemble proterocameroceratids in general form. Accordingly, Flower included the Endoceratdae and Piloceratidae, along with the Cyrtendoceratidae, in a suborder, the Endoceratina.

Genera

Flower restricted the Endoceratidae to those genera from the Middle and Upper Ordovician, and possibly Lower Silurian, belonging to the Endocerida with holochoantic or macrochoanitic septal necks and simple endocones. Teichert added '' Proterovaginoceras'', '' Triendoceras''. and '' Allocotoceras'' from the Lower Ordovician Genera included are: *'' Allocotoceras'' *''

'' *'' Chazyoceras'' *'' Endoceras'' *'' Foerstellites'' *'' Kotoceras'' *'' Kutorgoceras'' *'' Lamottoceras'' *'' Liskeardia'' *'' Nanno'' *'' Proterovaginoceras'' *'' Suecoceras'' *'' Tasmanoceras'' *'' Triendoceras'' *'' Vaginoceras'' *'' Vaningenoceras''

References

{{Taxonbar, from=Q5376231 Prehistoric nautiloid families Middle Ordovician first appearances Late Ordovician extinctions Nautiloids