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''Forresteria'' is an extinct genus of cephalopod belonging to the subclass Ammonoidea that flourished during the late Turonian and early Coniacian of the Late Cretaceous.〔Cobban, William A. ''et al'' (2006) "A USGS Zonal Table for the Upper Cretaceous Middle Cenomanian-Maastrichtian of the Western Interior of the United States Based on Ammonites, Inoceramids, and Radiometric Ages" () USGS (Open-File Report 2006–1250) 〕 and were global in extent. ''Forresteria alluaudi'' and ''Forresteria hobsoni'' are considered marker fossils for the lower Coniacian in the American West. ==Description== Although the whorl section and ornament of ''Forresteria'' are variable, it is easily distinguished from ''Barroisiceras'' by the presence of mid-lateral tubercles on the inner whorls, which later disappear or fuse with either umbilical or ventrolateral tubercles. Four subgenera are recognized 〔 W.J Arkell, et at, 1957 Mesozoic Ammonidea. Treatise on Invertebrate Paleontology, Part L Ammonoidea.〕 * ''F.(Forresteria)'': Whorl section moderately to very inflaced. Mid-lateral tubercles fuse with ventrolateral. * ''F.(Reesideoceras)'': Whorl section less inflated than with ''F.(Forresteria)''. Mid-lateral tubercles fuse with the umbilical. Keel disappears on outer whorl leaving venter flat or concave, bordered by ventrolateral clavi. * ''F. (Harleites)'': Shell compressed, with high keel and steep umbilical wall. Early whorls have weak umbilical, strong mid-lateral, and fine, feeble ventrolater tubercles. * ''F.(Zumpangoceras)'': Inclusion doubtful. Known only from crushed specimens from Mexico. Mid lateral tubercle strengthens with age. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Forresteria」の詳細全文を読む スポンサード リンク
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