|
| regnum = Animalia | phylum = Mollusca | classis = Cephalopoda | subclassis = Nautiloidea | ordo = Pseudorthocerida | familia = Carbactinoceratidae | genus = ''Rayonnoceras'' | genus_authority = Croneis, 1926 | subdivision_ranks = Species | subdivision = *see text}} ''Rayonnoceras'' is an extinct cephalopod genus that lived around 325 million years ago during the Carboniferous which although resembling earlier actinocerids is now though to belong to the Pseudorthocerida 〔Kröger, Björn, & Mapes, Royal 2007. Actinoceratoid Nautiloidea (Cephalopoda)— A new perspective; Journal of Paleontology Vol 81, No 4, pp 714-724, July 2007〕 ''Rayonnoceras'' is characterized by large straight shells with a large subcentral siphuncle composed of subglobular segments, as for the family.〔Teichert 1964, Treatise on Invertebrate Paleontology, K〕 The endosiphuncular canal system is well developed and most chambers are filled with organic deposits. Some shells have transverse striae, others are smooth. As with earlier actinocerids. ''Rayonnoceras'' too has a canal system within the siphuncle that includes a narrow opening between the internal deposits and inner wall of the connecting ring known as a parispatium. but differs from the earlier actinocerids in having a bullet-like apex with a cicatrix and a long first chamber, characteristic of pseuorthocerids, rather than a blunt apex and short first chamber characteristic of true actinocerids.〔 Recently, an eight-foot-long specimen of ''Rayonnoceras solidiforme'' was found in Arkansas, believed to be the largest of its kind ever found, is now housed at the University of Arkansas Museum. Orientation during life was horizontal. Cameral deposits, more concentrated in the apical part of the shell, are thought to have acted as ballast compensating for the weight of the animal in the forward part. In life ''Rayonnoceras'' was probably a bottom dweller that spent most of its time stationary, waiting in ambush for prey. ''Rayonnoceras'' was among the last of the actinocerid-mimics, which finally died out in the Carboniferous. ==References== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Rayonnoceras」の詳細全文を読む スポンサード リンク
|