20-634: † Cyrtendoceratidae † Endoceratidae † Proterocameroceratidae † Yorkoceratidae 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 Silurian . Their shells were variable in form. Some were straight ( orthoconic ), others curved (cyrtoconic); some were long (longiconic), others short (breviconic). Some long-shelled forms like Endoceras attained shell lengths close to 6 metres (20 ft). The related Cameroceras
40-810: A superorder instead. Rousseau Flower rejected this separation on the grounds that endocerids were no more diverse or complex than any other order. He considered them to be simply another order within the Nautiloidea. Flower (1958) divided the Endocerida into two suborders, the Proterocamerocerina and the Endocerina. As he defined the two suborders, Proterocamerocerina included the Proterocameroceratidae , Manchuroceratidae , and Emmonsoceratidae , while Endocerina included
60-692: A dozen cephalopod orders that appeared in the Lower Ordovician. They reached their greatest diversity during the Lower to Mid-Ordovician, but were already in decline by the middle of this period with most genera becoming extinct by the end of the Sandbian (late Ordovician), while some rare hangers on lasted into the Silurian . In any case, the endocerid lineage became completely extinct relatively early on in cephalopod history. Endocerids evolved from
80-461: Is an extinct genus of large, straight shelled cephalopods that gives its name to the Nautiloid order Endocerida . The genus lived during the middle and upper Ordovician 470 to 443 million years ago. 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
100-435: Is anecdotally reported to have reached lengths approaching 9 metres (30 ft), but these claims are problematic. The overwhelming majority of endocerids and nautiloids in general are much smaller, usually less than a meter long when fully grown. Endocerids had a relatively small body chamber as well as a proportionally large siphuncle , which in some genera reached nearly half the shell diameter. This suggests that much of
120-503: Is debated. Endocerids may have been the apex predators 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. Although there is study that supports filter feeding ecology, according to hydrostatic properties, it
140-411: Is not likely and still supports benthic predators. Endocerids laid relatively large eggs, and hatched at a relatively large body size. It is likely that endocerids were demersal after hatching, as large eggs would make an easy target for predators in the pelagic zone. Endocerids may have migrated from their habitat in the open ocean to shallower water to lay their eggs. Endocerids were among some half
160-644: 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
180-737: The Piloceratidae and Endoceratidae . Endocerid classification since then has relied on a dichotomy between short-shelled forms with complex endocones and long-shelled forms with simple endocones. Endocerid relationships have been difficult to establish both within the order and relative to other nautiloids. Their generally orthoconic shell shape and dorsomyarian muscle scars are similar to the subclass Orthoceratoidea , which are ancestral to ammonoids (ammonites) and coleoids (squid, octopus, etc.). However, their nautilosiphonate connecting ring structure and lack of cameral deposits are more similar to living nautilus and their proposed ancestors,
200-797: The Cyrtendoceratidae, in a suborder, the Endoceratina. 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: Endoceras Endoceras ( Ancient Greek for "inner horn")
220-484: The Orthocerida and Actinocerida . Endocerids reached enormous body sizes. The largest confirmed specimen, belonging to Endoceras giganteum , is 3 metres (9.8 ft) long as preserved, but is missing a substantial portion of its aboral end. The reconstructed length of the shell is nearly 6 metres (20 ft). An alleged endocerid specimen 30 feet (9.1 m) long is unconfirmed. The mode of life of endocerids
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#1732793160053240-474: The earlier ellesmerocerids , most likely from a genus similar to Pachendoceras . This ellesmerocerid gave rise to Proendoceras , the earliest representative of the Proterocameroceratidae and hence of the Endocerida. Endocerids evolved from ellesmerocerids by reduction of siphuncle diaphragms and the development of endocones. In the early part of the mid-Lower Ordovician, the Endocerida quickly diversified into many different families. In true endocerids, there
260-432: The more complex structures associated with the Proterocameroceratidae 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
280-644: The numerous piloceratid-like families were placed within a new order, Bisonocerida . Bisonocerida may still be related to endocerids within Endoceratoidea. Endoceratidae 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 . Endocerids are characterized by large, generally ventral siphuncles with simple endocones which lack
300-413: 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 Cameroceras and Vaginoceras the siphuncle is tubular with chambers formed adjacently from
320-411: The subclass Multiceratoidea . Some studies have re-established Endoceratoidea to clarify that endocerids occupy a unique subclass of nautiloids. Restudy of piloceratid-like families with complex endocones has suggested that Endocerida in its broadest form is polyphyletic , with piloceratid-like and proterocameroceratid-like members having independent origins from ellesmerocerids. In light of this issue,
340-624: 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. Endoceras was named by Hall in 1847. Distribution is widespread, especially in North America and Europe; and fossils have been found in Australia. Endoceras
360-492: The very start. The taxonomic significance of either in undetermined, other than as used to define a particular genus. The Endoceratidae arose from the upper Canadian (Lower Ordovician) Piloceratidae according to Rousseau Flower , which have similar simple structured siphuncles, although they may resemble proterocameroceratids in general form. Accordingly, Flower included the Endoceratdae and Piloceratidae, along with
380-495: 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 conical calcareous deposits, known as endocones, found in the more apical portion of the siphuncle. They are thought to act as a counterweight for the animal’s body. The chambers ( camerae ) of endocerids are always free of organic deposits, unlike orthoceratoid cephalopod orders such as
400-521: Was a trend of overall increasing size, eventually resulting in massive orthoconic genera such as Endoceras and Cameroceras . In another lineage (now known as Bisonocerida ), the siphuncle grew more complex, resulting in genera such as Chihlioceras and Allotrioceras . Citing its diversity, Curt Teichert (1964) placed the Endocerida in its own subclass called the Endoceroidea or Endoceratoidea (which some Russian paleontologists ranked as
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