Westonoceratidae are exogastric, mostly compressed,
Discosorida
Discosorida are an order of cephalopods that lived from the beginning of the Middle Ordovician, through the Silurian, and into the Devonian. Discosorids are unique in the structure and formation of the siphuncle, the tube that runs through an ...
of moderate size from the Middle
Ordovician
The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya.
T ...
to the Lower
Silurian.
The
siphuncle is typically close to the convexly curved outer margin of the phragmocone – the chambered part of the shell – taken to be ventral but may be more central in some genera. Connecting rings are thin to moderately thick with inflated bullettes grasping the previous septal foremina. Parietal deposits within the siphuncle from endocones in advanced genera and cameral deposits are found in some.
The Westonoceratidae are derived from the
Cyrtogomphoceratidae through the cyrtogomphoceratid, ''
Ulrichoceras''. In turn, the Westonoceratidae gave rise to a small group of discosorids, the
Lowoceratidae
The Lowoceratidae is a small family of discosorids, early nautiloid cephalopods, from the Middle Silurian in which the characteristic bullette is found only in early growth stages. Lowoceratids were first found in Southampton Island in the Ca ...
, which form an intermediary step before the
Discosoridae
Discosoridae comprise a family of endogastric discosorids, (Cephalopoda, Nautiloidea), with endocones in the siphuncle, ranging from the Middle Silurian to Middle Devonian.
Shell morphology
The shell in the Discosoridae is conical, expanding va ...
.
Two principal lineages have been identified, both stemming from the genus ''
Teichertoceras'', a derivative of ''Ulrichoceras''. One goes simply from ''
Westonoceras'' to ''
Winnipegoceras''. The other goes from ''
Faberoceras
''Faberoceras'' is an extinct genus of prehistoric nautiloid
Nautiloids are a group of marine cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and '' Allonautilus''. Fossil naut ...
'' to ''
Clarkesvillia'' to ''
Glyptodendron''. ''Faberoceras'' may also have given rise to ''
Hecatoceras'' and ''
Reedsoceras'' and is the likely source for the Lowoceratidae. Two other genera are included, but are separately derived from ''Ulrichoceras''. These are ''
Sinclairoceras'' and ''
Simardoceras''.
References
* Teichert, Curt 1964. Nautiloidea - Discosorida;
Treatise on Invertebrate Paleontology
The ''Treatise on Invertebrate Paleontology'' (or ''TIP'') published by the Geological Society of America and the University of Kansas Press, is a definitive multi-authored work of some 50 volumes, written by more than 300 paleontologists, and co ...
, Part K ; Geol Soc of America and University of Kansas Press
* Flower, R H and Teichert, C; 1957. The Cephalopod Order Discosorida. University of Kansas Paleontological Contributions. Mollusca, Article 6, pp 1–144.
{{Taxonbar, from=Q7989507
Discosorida
Middle Ordovician first appearances
Silurian extinctions
Prehistoric nautiloid families