Orthoceratoidea

Orthoceratoidea; Temporal range: Lower Ordovician–Upper Triassic PreꞒ Ꞓ O S D C P T J K Pg N Descendant taxon Coleoidea survives to the present
	Orthoconic nautiloid fossil from Morocco
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
Subclass:	†Orthoceratoidea; M'Coy 1844
Orders
	Riocerida (possibly paraphyletic); Dissidocerida (paraphyletic); Lituitida; Actinocerida; Pseudorthocerida; Orthocerida (paraphyletic);

Orthoceratoidea is a major subclass of nautiloid cephalopods. Members of this subclass usually have orthoconic (straight) to slightly cyrtoconic (curved) shells, and central to subcentral siphuncles which may bear internal deposits.^[1] Orthoceratoids are also characterized by dorsomyarian muscle scars (a small number of large scars concentrated at the top of the body chamber), extensive cameral deposits, and calciosiphonate connecting rings with a porous and calcitic inner layer.^[2]

Currently, Orthoceratoidea comprises the orders Riocerida, Dissidocerida, Actinocerida, Pseudorthocerida, Lituitida and Orthocerida.^[3] Orthocerida is a noteworthy paraphyletic order which is ancestral to the major cephalopod groups such as the extinct ammonoids and living coleoids (cephalopods without external shells, including squids, octopus, cuttlefish, etc.).^[2]^[3]

^ Kröger, B.; Evans, D. H. (2011). "Review and paleoecological analysis of the late Tremadocian – early Floian (Early Ordovician) cephalopod fauna of the Montagne Noire, France". Fossil Record. 14 (1): 5–34. doi:10.1002/mmng.201000013.
^ ^a ^b King, Andy H.; Evans, David H. (2019). "High-level classification of the nautiloid cephalopods: a proposal for the revision of the Treatise Part K". Swiss Journal of Palaeontology. 138 (1): 65–85. doi:10.1007/s13358-019-00186-4. ISSN 1664-2384. S2CID 133647555.
^ ^a ^b Pohle, Alexander; Kröger, Björn; Warnock, Rachel C. M.; King, Andy H.; Evans, David H.; Aubrechtová, Martina; Cichowolski, Marcela; Fang, Xiang; Klug, Christian (2022-04-14). "Early cephalopod evolution clarified through Bayesian phylogenetic inference". BMC Biology. 20 (1): 88. doi:10.1186/s12915-022-01284-5. ISSN 1741-7007. PMC 9008929. PMID 35421982.

[Kröger2011-1] Kröger, B.; Evans, D. H. (2011). "Review and paleoecological analysis of the late Tremadocian – early Floian (Early Ordovician) cephalopod fauna of the Montagne Noire, France". Fossil Record. 14 (1): 5–34. doi:10.1002/mmng.201000013.

[:2-2] King, Andy H.; Evans, David H. (2019). "High-level classification of the nautiloid cephalopods: a proposal for the revision of the Treatise Part K". Swiss Journal of Palaeontology. 138 (1): 65–85. doi:10.1007/s13358-019-00186-4. ISSN 1664-2384. S2CID 133647555.

[:1-3] Pohle, Alexander; Kröger, Björn; Warnock, Rachel C. M.; King, Andy H.; Evans, David H.; Aubrechtová, Martina; Cichowolski, Marcela; Fang, Xiang; Klug, Christian (2022-04-14). "Early cephalopod evolution clarified through Bayesian phylogenetic inference". BMC Biology. 20 (1): 88. doi:10.1186/s12915-022-01284-5. ISSN 1741-7007. PMC 9008929. PMID 35421982.

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