23-531: 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 . Lambeoceras is of medium to moderately large size with a long, straight, depressed shell, broad in cross section with the dorsum and venter both about equally convex, meeting acutely along the sides. Chambers are short, and septa are closely spaced, forming broad lobes on
46-667: A second wutinocerid genus, Adamsoceras . Gonioceras is an offshoot of an early Armenoceras; Lambeoceras and Huronia are offshoots of a later Actinoceras . The Actinoceratidae extend into the Lower Silurian with Actinoceras ; the Armenoceratidae and Huroniidae extend into the Upper Silurian. The Ormoceratidae are possibly the most recent, extending into the Lower Devonian Gonioceras (Gonioceratidae)
69-685: Is antedated by Wutinoceras , its assumed primitive nature rather a derived condition. Actinocerids first appeared early in the Middle Ordovician, with the exception of the Georginidae, which are known from the Cassinian in Northern Australia. They reached their greatest diversity in the Middle Ordovician with more than 20 genera, then declined somewhat in the Late Ordovician and more so in
92-583: Is limited to the Middle Ordovician, its quasi-lookalike Lambeoceras (Lamberoceratidae) to the uppermost Middle and Upper Ordovician. The wutinocerids are known only from the early Middle Ordovician (Whiterockian) and the polydesmiadids are restricted to about that time. Originating in the Ordovician, by the Devonian period actinocerids became rare; perhaps they were unable to compete with the more compact and maneuverable coiled nautiloids and ammonoids and cope with
115-534: Is unclear. The Upper Cambrian Protactinocerida have been suggested as being ancestral but none are known to have gone beyond the near end of the Cambrian extinction, which makes any connection hypothetical. Polydesmia was once thought to be the ancestral form of the actinocerids, and was derived from the ellesmeroceriid Bathmoceras . However, it turned out based on a reassessment of Lower Ordovician and Whiterockian formations in northeastern China that Polydesmia
138-735: The Early Silurian ; made a slight come back in the Middle Silurian but not to Late Ordovician numbers; and declined more or less steadily from the Late Silurian into the Devonian. Three major lineages began the Middle Ordovician, the Actinoceratidae, Armenoceratidae, and Ormoceratidae. The Actinoceratidae and Armenoceratidae are most likely derived from Wutinoceras and the Ormoceratidae from
161-665: The Ellesmerocerida as containing all archaic, ancestral cephalopods and established three suborders within: the Plectronoceratina, Ellesmeroceratina, and Cyrtocerinina. Furnish and Glenister, in the Treatise on Invertebrate Paleontology , Part K, essentially followed suit with minor differences at the family level. Mary Wade (1988) included the Ellesmerocerida in the superorder Plectonoceratoidea, which she defined as containing
184-833: The Burnam Limestone in central Texas ; with Actinoceras , Paractinoceras , and Kochoceras in the Lander Sandstone in Wyoming , and with Armenoceras . Actinoceras , and Selkirkoceras in the overlying dolomite – all of Red River age, marking the transition between the Middle and Upper Ordovician. Lambeoceras is also found with Actinoceras in the Dog Head member of the Red River Series in Manitoba and with Actinoceras and Kochoceras in
207-465: The Georginidae but don't become well established until the beginning of the early Whiterockian Stage (Dapingian) of the Middle Ordovician (Flower 1868,1976) The Georginidae, introduced and described by Mary Wade in 1977 (Wade 1988), based on the genus Georgina , are known from the upper Canadian Coolibah Formation of the Georgina Basin in Northern Australia. How the Georginidae relate to older stocks
230-641: The Huroniidae of the Silurian grew significantly larger. The Actinocerida inhabited shallow to quite deep waters, where they alternated between swimming and lying on the bottom. They were predatory, and able to control their buoyancy to a greater degree than their contemporaries. The derivation of the Actinocerida remains enigmatic. They first appear late in the Early Ordovician (Cassinian Stage, late Floian) with
253-601: The Mt. Silliman beds on Baffin Island . While the earlier Gonioceras no doubt rested on the sea floor in ambush, perhaps half buried or more in sediment, Lambeoceras may have more actively hunted in the water close to but above. On the other hand, Lambeoceras ' shape may have had more to do with stabilization in shallow surge ridden waters than with hunting methods. Actinocerida The Actinocerida are an order of generally straight, medium to large cephalopods that lived during
SECTION 10
#1732902571898276-566: The Plectronocerida, Ellesmerocerida and two orders introduced by Chen and Teichert in 1983, the Cambrian Yanhecerida and Protactinocerida. The Plectronocerida, also Cambrian, includes forms once included in the suborder Plectronoceratina, now elevated in rank. The Ellesmerocerida have been revised to include only primitive nautiloid cephalopods with thick connecting rings and siphuncle segments that are concave in outline. Accordingly,
299-796: The Protocycloceratidae, all which have thin tubular or expanded siphuncles, are now excluded. The Apocrinoceratidae , once included, is now assigned to the Discosorida The Ellesmerocerida are derived from the Plectronocerida , having first appeared early in the Trempealeauan Stage of the Late Cambrian and quickly diversifying into four families, only one of which, the Ellesmeroceratidae , continued by means of
322-558: The arrival of jawed fish. The Actinocerida contain nine families; the Georginidae, Wutinoceratidae, Polydesmiidae, Armenoceratidae, Ormoceratidae, Actinoceratidae, Gonioceratidae, Lambeoceratide, and Huroniidae. The Carbactinoceratidae, included in the taxonomy in the Treatise, (Vol K) have been removed to the Pseudorthocerida. Ellesmerocerida See text . The Ellesmerocerida is an order of primitive cephalopods belonging to
345-479: The early and middle Paleozoic , distinguished by a siphuncle composed of expanded segments that extend into the adjacent chambers, in which deposits formed within contain a system of radial canals and a narrow space along the inner side of the connecting ring known as a paraspatium. (Teichert 1964) Septal necks are generally short and cyrtochoanitic, some being recumbent, some hook shaped. Most grew to lengths of about 60 to 90 cm (2.0 to 3.0 ft) but some, like
368-670: The genera Ectenolites and Clarkoceras into the Gasconadian in the Lower Ordovician. The other three, Acaroceratidae , Huaiheceratidae , and Xiaoshanoceratidae having perished in the extinction event that occurred late in the Trempealeauan, before the end of the Cambrian. The dominant family of Ordovician Ellesmerocerida is the Ellesmeroceriatidae which are distinguished from the generally similar Protocycloceratidae by
391-585: The order includes the Ellesmeroceratidae , Protocycloceratidae , Cyclostomiceratidae , Bassleroceratidae , Eothinoceratidae , Bathmoceratidae , and Cyrtocerinidae . The Ellesmeroceratidae, Protocycloceratidae, Cyclostomiceratidae, Bassleroceratidae are found in Flower's basic Ellesmeroceratina. The Eothinoceratidae, Bathmoceratidae, and Cyrtocerinidae are combined in the Cyrtocerinina. The Schideleroceratidae, Apocrinoceratidae, Baltoceratidae and certain members of
414-646: The other hand, in the Treatise, thought that Lambeoceras was derived from Gonioceras and included it in the Gonioceratidae . Kochoceras differs from Lambeoceras in having a flattened venter and a siphuncle that rests on the ventral side and is closely allied with Actinoceras (Flower 1957) Lambeoceras is found with Actinoceras , Armenoceras , and Nybyoceras in the Second Value Formation in New Mexico ; with Armenoceras and Selkirkoceras in
437-617: The others in that their connecting rings are greatly thickened inwardly as annular lobes. The Ellesmerocerida gave rise to the Endocerida through Pachendoceras and to the Tarphycerida and Oncocerida through Bassleroceras and is the source for the Orthocerida , Pseudorthocerida , Actinocerida , and Discosorida . The Ellesmerocerida mostly died out by the end of the early Ordovician (Arenigian), although some stragglers survived until
460-545: The presence of broad lateral lobes in the suture. Sutures in the Protocycloceratidae are straight and transverse. Both contain forms that are annunlate (transversally ribbed) as well as smooth. Other Ordovician families are the broad and beviconic Cyclostomiceratidae and exogastric Bassleroceratidae, rounding out the Ellesmeroceratina. Three families, the Bathmoceratidae, Cyrtocerinidae, and Eothinoceratidae differ from
483-560: The previous septum. The siphuncle interior is commonly crossed by irregular partitions, known as diaphragms, but are otherwise free of internal deposits As soft parts are not prone to fossilization, little can be surmised as to their soft part anatomy. Preserved muscle attachment scars indicate that they may have had segmented muscles reminiscent of primitive monoplacophoran molluscs. As for arms or tentacles, little can be said except that eight or ten, retained in modern coleoids, seems to be Plesiomorphic in origin. Rousseau Flower defined
SECTION 20
#1732902571898506-987: The subclass Nautiloidea with a widespread distribution that lived during the Late Cambrian and Ordovician . The Ellesmerocerida are characterized by shells that are typically small, some even tiny, with close-spaced septa and relatively large ventral siphuncles. In some genera (e.g. Paleoceras ), the septa are uniformly spaced. Shells of ellesmerocerids are typically smooth and compressed and vary in form. They may be breviconic (short) or longiconic (elongate), straight (orthoconic) or curved (cyrtoconic). Cyrtoconic forms are usually endogastric, with longitudinally convex ventral margins. The apeces of straight forms typically have an endogastric curvature. Some may have grown to as much as 15 cm. Siphuncle segments are tubular or concave. Septal necks are short. Connecting rings which may appear layered are thick and typically wedge shaped with their maximum width at or near where they join
529-623: The upper and lower sides, which meet in sharp saddles along the sides. The siphuncle is submarginal, near the ventral side and relatively narrow. Septal necks are extremely long, brims short and recumbent. Segments are broadly expanded, connecting rings thin. Radial canals within the siphuncle from broad arcs that may bifurcate close to the parispatium. Lambeoceras is derived from the same stock in Actinoceras that produced Kochoceras according to Flower (1968), although consideration had been given to Armenoceras in Flower (1957). Teichert (1964) on
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