Temporal range: Jurassic
Zemistephanus is an extinct ammononite genus from the middle Jurassic of western North America and Western Australia, named by McLearn 1927. Zemistephanus is included in the sephanoceratoid family Otoitidae, which are characterized by shells that begin as barrel-shaped cadicones but which become planulate later in life. Body chambers are reduced in size and are excentric. Similar genera are Pseudotoites and Emileia
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- Arkell, W.J.; Kummel, B.; Wright, C.W. (1957). Mesozoic Ammonoidea. Treatise on Invertebrate Paleontology, Part L, Mollusca 4. Lawrence, Kansas: Geological Society of America and University of Kansas Press.
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