16-516: 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
32-573: 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. Gonioceras is derived from Armenoceras and is the type genus of Gonioceratidae . Fossils are found in marine strata of the Chazy and Blackriveran of the Middle Ordovician in the Champlain region of eastern North America and at
48-693: 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 the Burnam Limestone in central Texas ; with Actinoceras , Paractinoceras , and Kochoceras in
64-642: The Armenoceratidae and Huroniidae extend into the Upper Silurian. The Ormoceratidae are possibly the most recent, extending into the Lower Devonian Gonioceras (Gonioceratidae) 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
80-882: 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 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
96-819: 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 the Mt. Silliman beds on Baffin Island . While
112-608: The Middle Ordovician, the Actinoceratidae, Armenoceratidae, and Ormoceratidae. The Actinoceratidae and Armenoceratidae are most likely derived from Wutinoceras and the Ormoceratidae from 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 ;
128-599: The Paquette Rapids of the Ottawa River in Ontario. The type species , Gonioceras anceps was named by Hall in 1847. The flattened shell suggests that the living animal was a benthic organism. Actinocerida The Actinocerida are an order of generally straight, medium to large cephalopods that lived during the early and middle Paleozoic , distinguished by a siphuncle composed of expanded segments that extend into
144-640: 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 the Huroniidae of the Silurian grew significantly larger. The Actinocerida inhabited shallow to quite deep waters, where they alternated between swimming and lying on
160-412: 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 is antedated by Wutinoceras , its assumed primitive nature rather a derived condition. Actinocerids first appeared early in the Middle Ordovician, with the exception of
176-612: 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 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
SECTION 10
#1732901580597192-436: 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 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
208-520: 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 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
224-615: 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 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
240-552: 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 the other hand, in the Treatise, thought that Lambeoceras was derived from Gonioceras and included it in
256-542: The taxonomy in the Treatise, (Vol K) have been removed to the Pseudorthocerida. Lambeoceras 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
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