Specimen of Dawsonoceras annulatum, from here.

Belongs within: Orthoceratia.
Contains: Cycloceras, Dawsonoceratidae, Orthoceratidae, Paraphragmitidae, Geisonoceratidae.

The Michelinoceratida or Orthocerida were a Lower Ordovician to Upper Triassic assemblage of orthoconic or cyrtoconic cephalopods. This is perhaps the most systematically difficult group of fossil cephalopods and may be polyphyletic, with recent authors suggesting that some families (particularly the Pseudorthoceratidae) should be removed from the order.

The Middle Ordovician to Upper Silurian sactorthoceratid lineage includes the paraphyletic Sactorthoceratidae, Clinoceratidae and Ascocerida. The Sactorthoceratidae and Clinoceratidae were orthoconic or cyrtoconic longicones without endosiphuncular or cameral deposits (Sweet 1964). Septal necks were orthochoanitic or suborthochoanitic in Sactorthoceratidae and Ascocerida, cyrtochoanitic in Clinoceratidae (Furnish & Glenister 1964, Sweet 1964). Ascocerids were distinguished by inflated siphuncles and the periodic shedding of the apical parts of the conch; in the Ascoceratidae, the adoral portion of the conch became greatly swollen, followed by shedding of the juvenile section of the conch to produce a breviconic adult form (Furnish & Glenister 1964).

Characters (from Sweet 1964): Conchs straight to curved (never coiled), smooth or elaborately ornamented; cameral deposits typically well developed; siphuncles with orthochoanitic or secondarily cyrtochoanitic septal necks and thin connecting rings, empty or occupied by parietal or annulosiphonate deposits.

Orthoceratida (see below for synonymy)
    |    |--Sactorthoceras Kobayashi 1934 [incl. Sigmorthoceras Kobayashi 1934]S64
    |    |    `--*S. gonioseptum Kobayashi 1934S64
    |    |--Sigmocycloceras Kobayashi 1934S64
    |    |    `--*S. kogenense (Kobayashi 1927) [=Protocycloceras kogenense]S64
    |    `--+--Centroonoceras Kobayashi 1934 [incl. Cyrtoonoceras Flower 1939]S64
    |       |    |--*C. tokunagai (Kobayashi 1927) [=Ooceras tokunagai]S64
    |       |    `--C. josephianum (Foerste 1932)K93
    |       `--ClinoceratidaeS64
    |            |--Whiteavesites Foerste 1929S64
    |            |    `--*W. winnipegense (Whiteaves 1892) [=Orthoceras winnipegense]S64
    |            |--Clinoceras Mascke 1876 [=Clynoceras (l. c.)]S64
    |            |    |--*C. dens Mascke 1876S64
    |            |    |--C. exiguum [=Cyrtoceras exiguum]H84
    |            |    `--C. maskei (Dewitz 1879)K93
    |            `--Whitfieldoceras Foerste 1932S64
    |                 |--*W. mumiaeforme (Whitfield 1882) [=Oncoceras mumiaeforme]S64
    |                 |--W. baffinense Foerste 1932P68
    |                 |--W. minimum Foerste 1935P68
    |                 `--W. trentonense Foerste 1932P68
Orthoceratida incertae sedis:
  Chicagooceras Foerste & Savage 1927S64
    `--*C. welleri Foerste & Savage 1927S64
  Dictyoceras Eichwald 1860S64
    `--*D. porosum (Eichwald 1857) [=Orthoceras porosum]S64
  Garryoceras Foerste 1928S64
    `--*G. semiplanatum (Whiteaves 1892) [=Orthoceras semiplanatum]S64
  Heloceras Eichwald 1860S64
    `--*H. tuberculatum Eichwald 1860S64
  Loxoceras M’Coy 1844 [=Breynioceras Foerste 1929; Loxoceratidae]S64
    |--*L. breyni (Fleming 1828) [=Orthocera breyni, *Breynioceras breyni]S64
    |--L. husseyi Foerste 1923P68
    `--L. milleri (Foerste 1910) [=Orthoceras (Loxoceras) milleri]P68
  ‘Molossus’ deMontfort 1808 non Geoffroy 1805S64
    `--*M. gracilis (Blumenbach 1803) [=Orthoceratites gracilis]S64
  Neorthoceras Shimizu & Obata 1936S64
    `--*N. verbeeki (Haniel 1915) [=Orthoceras verbeeki]S64
  Sannionites Fischer de Waldheim 1829S64
    `--*S. crepitaculum Fischer de Waldheim 1829S64
  Subspyroceras Shimizu & Obata 1935S64
    `--*S. middlevillense (Foerste 1928) [=Spyroceras middlevillense]S64
  Tienoceras Chao 1954S64
    `--*T. lenticulare Chao 1954S64
  Tretoceras Salter 1858 [=Diploceras Salter 1856 non Conrad 1842, Tritoceras (l. c.)]S64
    `--*T. bisiphonatum (Sowerby in Murchison 1839) [=Orthoceras bisiphonatum, *Diploceras bisiphonatum]S64
  Sphooceras Flower 1962 [Sphooceratidae]S64
    |--*S. truncatum (Barrande 1860) [=Orthoceras truncatum]S64
    `--S. disjunctumKE19
  Offleyoceratidae [Folioceratidae]K93
    |--Offleyoceras Foerste 1928S64
    |    `--*O. arcticum (Foord 1888) [=Orthoceras arcticum]S64
         |--F. segmentum Collins 1969K93
         `--F. sulmenevense (Foerste 1925)K93
    |--Neosichuanoceras columinum Chen & Liu 1974K93
         |--J. cherkesovae Zhuravleva 1978K93
         `--J. yinkiangense Lai 1964K93
  Archigeisonoceras folkeslundenseM20

Orthoceratida [Michelinoceratida, Michelinoceratina, Michelinoceroida, Orthoceracea, Orthocerataceae, Orthoceratoidea, Orthocerida, Orthocerocea, Orthocerotida, Orthocerotoidea]

*Type species of generic name indicated


[H84] Hyatt, A. 1883–1884. Genera of fossil cephalopods. Boston Soc. Nat. History, Proc. 22: 253–338.

[K93] King, A. H. 1993. Mollusca: Cephalopoda (Nautiloidea). In: Benton, M. J. (ed.) The Fossil Record 2 pp. 169–188. Chapman & Hall: London.

[KE19] King, A. H., & D. H. Evans. 2019. High-level classification of the nautiloid cephalopods: a proposal for the revision of the Treatise Part K. Swiss Journal of Palaeontology 138: 65–85.

[M20] Mutvei, H. 2020. Restudy of some plectronocerid nautiloids (Cephalopoda) from the late Cambrian of China; discussion on nautiloid evolution and origin of the siphuncle. GFF 142 (2): 115–124.

[P68] Purnell, L. R. 1968. Catalog of the type specimens of invertebrate fossils. Part I: Paleozoic Cephalopoda. United States National Museum Bulletin 262: 1–198.

[S64] Sweet, W. C. 1964. Nautiloidea—Orthocerida. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt K. Mollusca 3. CephalopodaGeneral FeaturesEndoceratoideaActinoceratoideaNautiloideaBactritoidea pp. K216–K261. The Geological Society of America and the University of Kansas Press.

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