Didymoceras

Didymoceras is an extinct genus of ammonite cephalopod from the Late Cretaceous epoch (approximately 76 Ma). It is one of the most bizarrely shaped genera, with a shell that spirals upwards into a loose, hooked tip. It is thought to have drifted in the water vertically, moving up and down. The generic name is Greek for "paired horns".

Didymoceras Temporal range: Upper Campanian PreꞒ Ꞓ O S D C P T J K Pg N
Artist's reconstruction of D. stevensoni, D. nebrascensis, and D. cheyennese
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
Subclass:	†Ammonoidea
Order:	†Ammonitida
Suborder:	†Ancyloceratina
Family:	†Nostoceratidae (?)
Genus:	†Didymoceras Hyatt, 1894
Species
See text
Synonyms
Cirroceras Conrad, 1866 Helicoceras d'Orbigny, 1842 Helicoceras Whitfield, 1877 Emperoceras Hyatt, 1894 Didymoceratoides Kennedy & Cobban, 1993

Its taxonomic place is often in flux, being placed in either Turrilitidae, Nostoceratidae, or its own family, Didymoceratidae. Species included in the genus are the following:^[1][2]

D. stevensoni shell exhibit in the Houston Museum of Natural Science

• Didymoceras angulatum (Meek and Hayden, 1860)
• Didymoceras binodosum Kennedy and Cobban, 1993
• Didymoceras californicum Anderson, 1958
• Didymoceras cheyenense (Meek and Hayden, 1856)
• Didymoceras cheyennense (Meek and Hayden, 1856)
• Didymoceras cochleatus (Meek and Hayden, 1858)
• Didymoceras hidakense Shigeta in Shigeta et al., 2016
• Didymoceras hornbyense (Whiteaves, 1876)
• Didymoceras navarroensis (Shumard, 1861)
• Didymoceras nebrascense Meek and Hayden, 1856)
• Didymoceras newtoni (Whitfield, 1877)
• Didymoceras nicolletii (Hall and Meek, 1856)
• Didymoceras platycostatum Kennedy and Cobban, 1993
• Didymoceras stevensoni (Whitfield, 1877)
• Didymoceras subtuberculatum Howarth, 1965
• Didymoceras tenuicostatus (Meek and Hayden, 1858)
• Didymoceras tortus (Meek and Hayden, 1858)
• Didymoceras tricostatus (Whitfield, 1897)
• Didymoceras umbilicatu (Meek and Hayden, 1858)
• Didymoceras uncus (Meek and Hayden, 1858)
• Didymoceras vespertinus (Conrad, 1874)