Dissidocerida is an order of Early

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

to the Early Silurian orthoceratoid cephalopods in which the

siphuncle The siphuncle is a strand of biological tissue, tissue passing longitudinally through the mollusc shell, shell of a cephalopod mollusc. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the li ...

has a continuous lining or a longitudinal rod-like structure within. The order Dissidocerida was proposed by Zhuravleva (1994) for ''Dissidoceras undosum'' Zhuravleva, 1964, a Silurian orthoconic genus with a wide, nearly central, tubular

, suborthochoanitic septal necks, and endosiphuncular rod; in many aspects similar to rod-bearing orthocones of the Ordovician. It is thought by some that Ordovician-Silurian orthocones with continuous longitudinal endosiphuncular laminar deposits constitute a single phylogenetic stock. The Dissidocerida as understood includes the Polymeridae, Rangeroceratidae, Troedssonellidae, and Dissidocertidae. The Polymeridae and Rangeroceratidae were proposed by Evans in 2005 for ''Polymeres'' Murchison 1839 and ''Rangeroceras'' Hook and Flower 1977, respectively. Troedssonellidae was established by Kobayashi in 1935 and is based on the genus ''Troedssonella''. The Dissidoceratidae was established by Zhuravleva for ''Dissidoceras undosum''

References

* A. A. Shevyrev 2004, The Cephalopod Macrosystem: A Historical Review, the Present State of Knowledge, and Unsolved Problems: 2. Classification of Nautiloid Cephalopods. * Bjorn Kroger, 2008. A new genus of middle Tremadocian orthoceratoids and the Early Ordovician origin of orthoceratoid cephalopods. Brief Report Acta Palaeontologica Polonica 53 (4): 745–749
Paleobiology -Dissidocerida
{{Taxonbar, from=Q5282776 Orthoceratoidea Prehistoric cephalopod orders Ordovician cephalopods Silurian cephalopods Ordovician first appearances Silurian extinctions