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标题：The heteromorph ammonite Didymoceras cochleatum (Meek and Hayden, 1858), from the Pierre Shale of South Dakota and Wyoming. American Museum novitates ; no. 3268
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作者：Kennedy, W. J. ; Cobban, William Aubrey ; Landman, Neil H. 等
期刊名称：American Museum Novitates
印刷版ISSN：0003-0082
电子版ISSN：1937-352X
出版年度：1999
卷号：1999
语种：
出版社：American Museum of Natural History
摘要："The middle Campanian (Upper Cretaceous) zone of Baculites gregoryensis Cobban, 1951 in south-central South Dakota and eastern Wyoming has yielded numerous fragments of a distinctive species of Didymoceras characterized by initial loose planispiral whorls followed by loose helical whorls, and finally by a slightly pendant body chamber. These fragments are referred to Didymoceras cochleatum (Meek and Hayden, 1858), a species based on one-half of a septate whorl from the helical growth stage. This species is abundant in the Gregory Member of the Pierre Shale along the Missouri River Valley in South Dakota, rare in the Red Bird Silty Member of the Pierre Shale in eastern Wyoming, and very rare in the Rock River Formation in southeastern Wyoming"--P. [1].