Discosorida

Reconstruction of the Middle Silurian Mandaloceras, from Palaeos.com.

Belongs within: Cephalopoda.
Contains: Westonoceratidae, Cyrtogomphoceratidae.

The Middle Ordovician to Middle Devonian Discosorida were an order of mostly breviconic or cyrtoconic cephalopods. The major distinguishing feature of the group was the development of thick, layered connecting rings around the siphuncle that overlapped the septal necks to form mineralised protrusions called bullettes.

Characters (from Teichert 1964): Medium-sized to large brevicones, short cyrtocones, or rarely orthocones; endogastric, rarely exogastric; siphuncle usually with broadly expanded segments, central to marginal; connecting rings usually thick, complex; endosiphuncular deposits occasionally present.

<==Discosorida
    |--+--Westonoceratidae T64
    |  `--Cyrtogomphoceratidae T64
    `--Ruedemannoceratidae T64
         |--Ruedemannoceras Flower 1940 [Ruedemannoceratidae] T64
         |    `--*R. boycii (Whitfield 1886) [=Cyrtoceras boycii] T64
         |--Franklinoceras Flower 1957 T64
         |    `--*F. elongatum Flower 1957 T64
         `--+--Madiganella Teichert & Glenister 1952 T64
            |    `--*M. magna Teichert & Glenister 1952 T64
            `--Mandaloceratidae T64
                 |--Pseudogomphoceras Flower in Flower & Teichert 1957 T64
                 |    `--*P. rigidum (Barrande 1865) [=Gomphoceras rigidum] T64
                 `--+--Mesoceras Barrande 1877 [Mesoceratidae] T64
                    |    `--*M. bohemicum Barrande 1877 T64
                    |--Cinctoceras Flower in Flower & Teichert 1957 T64
                    |    `--*C. imperiale (Barrande 1865) [=Gomphoceras imperiale] T64
                    |--Umbeloceras Flower in Flower & Teichert 1957 T64
                    |    `--*U. spei (Barrande 1865) [=Gomphoceras spei] T64
                    |--Cayugoceras Flower 1947 T64
                    |    `--*C. semiclausum (Barrande 1865) [=Gomphoceras semiclausum] T64
                    |--Ovocerina Flower 1947 T64
                    |    |--*O. marsupium (Barrande 1865) [=Gomphoceras marsupium] T64
                    |    `--O. alphaeus T64
                    `--+--Vespoceras Flower in Flower & Teichert 1957 T64
                       |    `--*V. vespa (Barrande 18650 [=Gomphoceras vespa] T64
                       `--Mandaloceras Hyatt in Zittel 1900 T64
                            |--*M. bohemicum (Barrande 1865) [=Gomphoceras bohemicum] T64
                            |--M. austini Foerste 1934 P68
                            |--M. hawthornense Foerste 1930 P68
                            `--M. subgracile P68

*Type species of generic name indicated

REFERENCES

[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.

[T64] Teichert, C. 1964. Nautiloidea – Discosorida. In Treatise on Invertebrate Paleontology pt. K. Mollusca 3. Cephalopoda – General Features – Endoceratoidea – Actinoceratoidea – Nautiloidea – Bactritoidea (R. C. Moore, ed.) pp. K320-K342. The Geological Society of America and the University of Kansas Press.