Endoceratidae, from

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

ἔνδον (''éndon''), meaning "inside", and κέρας (''kéras''), meaning "horn", is a family of large to very large straight-shelled

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

cephalopods belonging to the order

Endocerida Endocerida, from Ancient Greek ἔνδον (''éndon''), meaning "inside", and κέρας (''kéras''), meaning "horn", is an extinct nautiloid order, a group of cephalopods from the Lower Paleozoic with cone-like deposits in their siphuncle. End ...

that lived during the Middle and Late

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

. They include the largest known

Paleozoic The Paleozoic ( , , ; or Palaeozoic) Era is the first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma a ...

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

Cameroceras ''Cameroceras'', from Ancient Greek καμάρα (''kamára''), meaning "chamber", and κέρας (''kéras''), meaning "horn", is an extinct genus of endocerid cephalopod which lived in equatorial oceans during the entire Ordovician period. Lik ...

''.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 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. Proterocamerocerat ...

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 Nanno () was a ''comune'' (municipality) in Trentino in the northern Italian region Trentino-Alto Adige/Südtirol, located about north of Trento. As of 31 December 2004, it had a population of 623 and an area of .All demographics and other stati ...

'' 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 () 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 their being ''C ...

(Lower Ordovician)

Piloceratidae The Piloceratidae are a compressed, rapidly expanding, cyrtoconic brevicones with holochoanitic ventral siphuncles and simple endocones. Most likely evolved from '' Clitendoceras'', a narrow, slightly endogastric genus intermediate in form betwee ...

according to

Rousseau Flower Rousseau Hayner Flower (1913–1988) was an extremely prolific 20th century paleontologist, known for his eccentric personality. Career Although trained as an entomologist, and a specialist in dragonflies and orthopterans, Flower began study ...

,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 The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...

, belonging to the Endocerida with holochoantic or macrochoanitic septal necks and simple endocones. Teichert added '' Proterovaginoceras'', '' Triendoceras''. and ''

Allocotoceras ''Allocotoceras'' is an Endocerida, endocerid from the Lower Ordovician (upper Canadian) Karmberg Formation of Australia (Tasmania),Allocotoceras ''Allocotoceras'' is an Endocerida, endocerid from the Lower Ordovician (upper Canadian) Karmberg Formation of Australia (Tasmania),Cameroceras ''Cameroceras'', from Ancient Greek καμάρα (''kamára''), meaning "chamber", and κέρας (''kéras''), meaning "horn", is an extinct genus of endocerid cephalopod which lived in equatorial oceans during the entire Ordovician period. Lik ...

'' *'' Chazyoceras'' *'' Endoceras'' *'' Foerstellites'' *'' Kotoceras'' *'' Kutorgoceras'' *'' Lamottoceras'' *'' Liskeardia'' *''

'' *'' Proterovaginoceras'' *'' Suecoceras'' *'' Tasmanoceras'' *'' Triendoceras'' *'' Vaginoceras'' *'' Vaningenoceras''

References

{{Taxonbar, from=Q5376231 Prehistoric nautiloid families Middle Ordovician first appearances Late Ordovician extinctions Endoceratidae Fossil taxa described in 1884