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Temporal range: M-U Ordovician
Specimens in Milan
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Nautiloidea
Order: Endocerida
Family: Endoceratidae
Genus: Endoceras
Hall, 1847

Endoceras (Ancient Greek for "inner horn") is an extinct genus of large, straight shelled cephalopods from the Middle and Upper Ordovician that gives its name to the Nautiliod order Endocerida. The cross section in the mature portion is slightly wider than high, but is narrower laterally in the young. Sutures are straight and transverse. Endoceras has a large siphuncle, located close to the ventral margin, composed of concave segments, especially in the young but which may be tubular in the adult stage. Endocones are simple, subcircular in cross section, and penetrated by a narrow tube which may contain diaphragms reminiscent of the Ellesmerocerid ancestor.

Specimen from Stevns, Denmark Endoceras.jpg
Specimen from Stevns, Denmark

Endoceras was named by Hall in 1847. Distribution is widespread, especially in North America and Europe. Endoceras is similar to Cameroceras , the two may be synonymous, but differs from the genus Nanno in that the siphuncle in Nanno fills the entire apical portion of the shell while in Endoceras the siphuncle is ventral even there with septa formed at the onset.

Mature, full grown, Endoceras were most likely ambush predators that lay in wait on the sea floor, moving when necessary to gain the advantage. Younger individuals with compressed cross sections may have been more actively mobile.


A specimen of Endoceras giganteum at the Museum of Comparative Zoology measures 3 meters (9.8 ft) as preserved. [1] The most recent estimate puts its complete size at 5.7 meters (18.7 ft). This would make it the largest cephalopod by length in the fossil record. [2] There is additionally an unconfirmed report of a 9.1 meter (30 ft) shell that was destroyed. [3]

Related Research Articles

Endocerida Fossil order of cephalopods

Endocerida is an extinct nautiloid order, a group of cephalopods from the Lower Paleozoic with cone-like deposits in its siphuncle.

Cameroceras 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 component of the fauna in some places during the period, inhabiting the shallow seas of Laurentia, Baltica and Siberia. Its diversity and abundance became severely reduced following the Ordovician–Silurian extinction events, and the last remnants of the genus went extinct sometime during the Wenlock.

Suecoceras is an endoceratid that lived during the Middle Ordovician. It is characterised by a long, straight, slender shell with a slightly expanded tip that curves slightly downwards.

Proterocameroceratidae Extinct family of nautiloids

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.

Piloceratidae Extinct family of nautiloids

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 between straight shelled Proendoceras and the bulkier Piloceratidae. Found in shallow carbonate marine sediments of Demingian through the Cassinian age,.

Actinoceras is the principal and root genus of the Actinoceratidae, a major family in the Actinocerida, that lived during the Middle and Late Ordovician.

Lambeoceras is a genus of large actinocerids with a convexly lenticular cross section from the Upper Ordovician of North America and the sole representative of the family Lambeoceratidae.

Gonioceras is an extinct genus of actinocerid nautiloidean cephalopods typified by a broad, low shell; flattened ventrally, convexly rounded dorsally; top and bottom meeting at an acute angle along the sides. In most the shell is rather thin, especially along the lateral portion. The aperture is contracted. Sutures from broad ventral and dorsal lobes, more narrowly rounded ventro-lateral and dorso-lateral saddles, and sharp pointed lateral lobes; more complex than in later Lambeoceras. The siphuncle is typically subcentral but may be closer to the venter; armenocerid in form with short segments and very short brims and containing a straight endosiphuncular canal system.

<i>Aturia</i> Extinct genus of molluscs

Aturia is an extinct genus of Paleocene to Miocene nautilids within Aturiidae, a monotypic family, established by Campman in 1857 for Aturia Bronn, 1838, and is included in the superfamily Nautilaceae in Kümmel 1964.

Williamsoceras is an endocerid that Rousseau Flower (1968) added to his Allotrioceratidae on the basis of having a vertical partition within the siphuncle, known as a ventral process, with inter-connecting tubule-like structures along its margin where intercepted by endocones. Three species are named and described from the Garden City limestone of Whiterockian age near Logan and northern Utah, including the genotype Williamsoceras adnatum. Two other species come from the Juab limestone of near equivalent age in the southern Confusion Range in the Ibex area in western Utah.

Westonoceras is an extinct nautiloid genus from the Discosorida that lived during the Middle and Late Ordovician that has been found in North America, Greenland, and Northern Europe. It is the type genus for the Westonoceratidae

Phragmoceratidae Extinct family of molluscs

The Phragmoceratidae is a family of extinct nautiloid cephalopods from the Order Discosorida that lived during the latter part of the Silurian.

Mandaloceratidae is a family in the nautiloid cephalopod order Discosorida, from the Middle and Upper(?) Silurian characterized by short, essentially straight shells referred to as breviconic, typically with a faintly exogastric shape produced by the profile of the body chamber.

Endoceratidae is a family of large to very large straight shelled nautiloid cephalopods belonging to the order Endocerida that lived during the Middle and Late Ordovician. They include the largest known Paleozoic invertebrates, represented by Endoceras and Cameroceras.

Pentameroceras is a straight to slightly exogastric breviconic oncocerid from the middle Silurian of North America and Europe belonging to the Trimeroceratidae.

Ophioceras is a genus of closely coiled tarphycerid nautiloid cephalopods, the sole representatives of the family Ophidioceratidae, characterized by an evolute shell with narrow, subrounded, annulated whorls and a subcentral siphuncle composed of thin connecting rings that show no evidence of layering. The mature body chamber is strongly divergent and is the longest proportionally of any tarphycerid. The aperture has a deep hyponomic sinus and ocular sinuses, and so resembles some lituitids.

Intejocerida is the name given to a group of generally straight shelled nautiloid cephalopods originally found in Lower and Middle Ordovician sediments in the Angara River basin in Russia; defined in the Treatise as an order, and combined there with the Endocerida in the Endoceratoidea.

Proterovaginoceras is a medium to large sized endocerid from the Early and Middle Ordovician included in the family Endoceratidae.

Simardoceras is a genus in the discosorid family Westonoceratidae from the Middle Ordovician of Quebec.

Discosoridae comprise a family of endogastric discosorids,, with endocones in the siphuncle, ranging from the Middle Silurian to Middle Devonian.


  1. Teichert, C.; Kummel, B. (1960). "Size of endoceroid cephalopods". Breviora. 128: 1–7.
  2. Klug, C.; De Baets, K.; Kröger, B.; Bell, M.A.; Korn, D.; Payne, J.L. (2015). "Normal giants? Temporal and latitudinal shifts of Palaeozoic marine invertebrate gigantism and global change". Lethaia. 48 (2): 267–288. doi:10.1111/let.12104.
  3. Flower, R.H. (1955). "Status of endoceroid classification". Journal of Paleontology. 29 (3): 329–371. JSTOR   1300321.