''Hipparionoceras'' is a genus of
oncocerids from the middle Devonian of Europe, North America, and China that lived around 395 million years ago.
The shell of ''Hipparionoceras'' is curved, rapidly expanding, flared toward the aperture. The curvature is endogastric with the ventral side somewhat concave in profile.
The siphuncle is subventral, empty, with segments expanded into the short but broad chambers. Septa are close spaced, their curvature shallow.
''
Polyelasmoceras'' and ''
Macrodomoceras
''Macrodomoceras'' is a genus of oncocerids, family Polyelasmoceratidae, from the Middle Devonian of Australia.
The shell of ''Macrodomoceras'' is a compressed, endogastric cyrtocone, i.e. section higher than wide and curved with the ventral sid ...
'' are related genera, also from the Middle Devonian. ''
Cadoceras
''Cadoceras'' is an extinct ammonite genus belonging to the Cardioceratidae that lived during the Jurassic period from the late Bajocian to the early Callovian
In the geologic timescale, the Callovian is an age and stage in the Middle Jurassic, ...
'' from the Middle
Silurian
The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...
may be ancestral.
References
* Walter C. Sweet, 1964. Nautiloidea-Oncocerida. Treatise on Invertebrate Paleontilogy, Part K. Geological Society of America.
Hipparionocerasin Fossilworks Gateway
Prehistoric nautiloid genera
Oncocerida
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