''Didymoceras'' is an extinct
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
ammonite
Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...
cephalopod
A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...
from the
Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...
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".
Its taxonomic place is often in flux, being placed in either
Turrilitidae
Turrilitidae is a family of extinct heteromorph ammonite cephalopods. All members had shells that coiled helically that tended to resemble auger shells. The ecological roles turrilitids played is largely unknown, as experts are still speculati ...
,
Nostoceratidae
Nostoceratidae is a diverse Family (biology), family of heteromorph ammonites found throughout the oceans of the world during the Late Cretaceous. The nostoceratids are famous for the bizarre coiling of their shells. Many genera, such as ''Yezo ...
, or its own family, Didymoceratidae. Species included in the genus are the following:
*''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
''Didymoceras nebrascense'' was an extinct species of heteromorph ammonite from the upper Campanian age (around 83 to 70 million years ago). It was sexually dimorphic, with two adult sizes averaging at and high for females and males respectivel ...
''
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)
References
Ammonitida genera
Nostoceratidae
Cretaceous ammonites
Late Cretaceous ammonites of North America
Taxa named by Alpheus Hyatt
{{Ammonitida-stub