Cunningtoniceras
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''Cunningtoniceras'' is a stocky acanthoceratid ammonite from the upper
Cenomanian The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in the s ...
stage of the late Cretaceous of the western
U.S. The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
, found e.g. in Arizona and New Mexico. ''Cunningtoniceras'' was proposed by Maurice Collignon, 1927, for ribbed, evolute ammonites having a quadrangular whorl section; umbilical, inner and outer ventrolateral, and siphonal (i.e. mid-ventral) tubercles; a venter with a multiplication of ribs and tubercles, or one or the other. Ornament weakens with age except for the inner ventrolateral tubercles, which enlargen. Cobban, Hook & Kennedy, 1989, distinguish ''Cunningtoniceras'' Collignon from ''
Euomphaloceras ''Euomphaloceras'' is an early Upper Cretaceous ammonite genus, (Cephalopoda, Ammonoidea), included in the Acanthoceratinae until established as the type genus for the Euomphaloceratinae Euomphaloceratinae is a subfamily of Upper Cretaceous am ...
'' Spath 1923, the two having been previously regarded as synonymous. In fact ''Cunningtoniceras'' is described in the Treatise L, 1957 as a synonym of ''Euomphaloceras'', noted as having three rows of small tubercles on a broad flat venter. Although ''Cunningtonicaras'' and ''Euomphaloceras'' share many characters, both belonging to the Acanthoceratidae, they are distinguished by the nature of the first lateral lobe of their respective sutures. The first lateral lobe of species ultimately assigned to ''Cunningtonicaras'' are narrow and bifid, contrasting with the broad and deeply bifid lobes of ''Euomphalooceras''.


References

* W.J. Arkell ''et al.'', 1957. Mesozoic Ammonoidea; Treatise on Invertebrate Paleontology, Part L. Geological Society of America, R.C. Moore (ed). * W.A. Cobban, S.C. Hook & W.J.Kennedy, 1989. Upper Cretaceous rocks and ammonite faunas of southwestern New Mexico. Memoir 45, New Mexico Bureau of Mines & Mineral Resources. Acanthoceratidae Ammonitida genera Late Cretaceous ammonites of North America Cenomanian life {{ammonitina-stub