Plectronoceratids are known from the Upper Cambrian (upper Franconian – middle Trempealeauan) of China and North America (Minnesota, Wisconsin). Two families are recognized (Flower, 1964),[3] the generally straight to endogastric Plectronoceratidae and the slightly exogastric Balkoceratidae.
Diagnostic charactersEdit
Members of the Plectronocerida are characterized as follows. Shells are generally small, some even tiny, laterally compressed, curved (cyrtoconic) or straight (orthoconic). Most cyrtoconic forms are endogastric, with the ventral side longitudinally concave, or the dorsal side more longitudinally convex. A few, the two known genera in Balkoceratidae are exogastrically curved, with the ventral side convex and dorsal side concave. Septa are close spaced, in some less than a millimeter. Siphuncles are ventral, and in most, proportionally large. Connecting rings are in general poorly calcified and may expand as siphonal bulbs into the chambers where not restricted by septal necks.[3]
As with all shelled cephalopods, plectronocerids had a tube called a siphuncle, which let them fill the chambers of their phragmocone with gas instead of water, thus controlling their buoyancy.[4] They were not, however, adapted for jet-powered swimming.
PhylogenyEdit
The Plectronoceratida gave rise in the Late Cambrian (early and middle Trempealeauan) to the other three plectronoceratoid orders, the Ellesmerocerida and Protactinocerida and Yanhecerida. The Plectronoceratidae gave rise to the other ellesmerocerid families, including the Upper Cambrian exogastric Balkoceratidea, and with remote possibility to the Discosorida. The Balkoceratidae are unrelated to later exogastric forms that first appeared in the Ordovician.
EcologyEdit
Plectronocerids were probably benthic animals that crawled along the bottom in search of food or safety, facing downwards, with the shell carried above. Nothing is known of their specific soft-part anatomy or to what extent tentacles, if any, had developed.
^Curt Teichert, 1988. Main Features of Cephalopod Evolution. The Mollusca Vol. 12 Paleontology and Neontology of Cephalopds; Academic Pres Inc.
^ abFlower, Rousseau H. 1964. The Nautiloid Order Ellesmeroceratida (Cephalopoda); Memoir 12, New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico
^Mutvei, H.; Zhang, Y.; Dunca, E. (2007). "Late Cambrian Plectronocerid Nautiloids and Their Role in Cephalopod Evolution". Palaeontology. 50 (6): 1327–1333. doi:10.1111/j.1475-4983.2007.00708.x.
Further readingEdit
Flower, Rousseau H. (1955). "Saltations in Nautiloid Coiling". Evolution. 9 (3): 244–260. doi:10.2307/2405647. JSTOR 2405647.
plectronocerida, primitive, order, from, which, subsequent, cephalopod, orders, ultimately, derived, temporal, range, upper, cambrian, preꞒ, nplectronoceras, life, restorationscientific, classificationdomain, eukaryotakingdom, animaliaphylum, molluscaclass, ce. Plectronocerida is a primitive order from which subsequent cephalopod orders are ultimately derived 1 2 PlectronoceridaTemporal range Upper Cambrian PreꞒ Ꞓ O S D C P T J K Pg NPlectronoceras life restorationScientific classificationDomain EukaryotaKingdom AnimaliaPhylum MolluscaClass CephalopodaSubclass NautiloideaSuperorder PlectronoceratoideaOrder PlectronoceridaTeichert 1988Families and generaPlectronoceratidae Plectronoceras Paraplectronoceras Eodiaphragmoceras Jiagouceras Lunanoceras PaleocerasBalkoceratidae Balkoceras Theskaloceras Contents 1 Occurrence 2 Diagnostic characters 3 Phylogeny 4 Ecology 5 References 6 Further readingOccurrence EditPlectronoceratids are known from the Upper Cambrian upper Franconian middle Trempealeauan of China and North America Minnesota Wisconsin Two families are recognized Flower 1964 3 the generally straight to endogastric Plectronoceratidae and the slightly exogastric Balkoceratidae Diagnostic characters EditMembers of the Plectronocerida are characterized as follows Shells are generally small some even tiny laterally compressed curved cyrtoconic or straight orthoconic Most cyrtoconic forms are endogastric with the ventral side longitudinally concave or the dorsal side more longitudinally convex A few the two known genera in Balkoceratidae are exogastrically curved with the ventral side convex and dorsal side concave Septa are close spaced in some less than a millimeter Siphuncles are ventral and in most proportionally large Connecting rings are in general poorly calcified and may expand as siphonal bulbs into the chambers where not restricted by septal necks 3 As with all shelled cephalopods plectronocerids had a tube called a siphuncle which let them fill the chambers of their phragmocone with gas instead of water thus controlling their buoyancy 4 They were not however adapted for jet powered swimming Phylogeny EditThe Plectronoceratida gave rise in the Late Cambrian early and middle Trempealeauan to the other three plectronoceratoid orders the Ellesmerocerida and Protactinocerida and Yanhecerida The Plectronoceratidae gave rise to the other ellesmerocerid families including the Upper Cambrian exogastric Balkoceratidea and with remote possibility to the Discosorida The Balkoceratidae are unrelated to later exogastric forms that first appeared in the Ordovician Ecology EditPlectronocerids were probably benthic animals that crawled along the bottom in search of food or safety facing downwards with the shell carried above Nothing is known of their specific soft part anatomy or to what extent tentacles if any had developed References Edit Jun Yuan Chen Teichert Curt 1983 Cambrian cephalopods Geology 11 11 647 Bibcode 1983Geo 11 647J doi 10 1130 0091 7613 1983 11 lt 647 CC gt 2 0 CO 2 Curt Teichert 1988 Main Features of Cephalopod Evolution The Mollusca Vol 12 Paleontology and Neontology of Cephalopds Academic Pres Inc a b Flower Rousseau H 1964 The Nautiloid Order Ellesmeroceratida Cephalopoda Memoir 12 New Mexico Bureau of Mines and Mineral Resources Socorro New Mexico Mutvei H Zhang Y Dunca E 2007 Late Cambrian Plectronocerid Nautiloids and Their Role in Cephalopod Evolution Palaeontology 50 6 1327 1333 doi 10 1111 j 1475 4983 2007 00708 x Further reading EditFlower Rousseau H 1955 Saltations in Nautiloid Coiling Evolution 9 3 244 260 doi 10 2307 2405647 JSTOR 2405647 Furnish W M Glenister B F 1964 Nautiloidea Ellesmerocerida Treatise on Invertebrate Paleontology K K129 Retrieved from https en wikipedia org w index php title Plectronocerida amp oldid 1139285210, wikipedia, wiki, book, books, library,
