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''Harpoceratinae'' is an extinct subfamily of cephalopods belonging to the family Hildoceratidae. Ammonites of this subfamily had involute and compressed shells with strong keels. Keel might be rarely missing, but this is considered to be an abnormality. This has been observed both in ''Cleviceras'' and ''Harpoceras'' and called as genus ''Monestieria'', which is now known to be invalid (into this invalid genus were added also abnormal unkeeled specimens of genus ''Protogrammoceras''). Another example is ''Pseudolioceras'', whose unkeeled specimen was used as type for description of invalid genus ''Praehaploceras''. Oxyconic forms of this subfamily (''Polyplectus'' and ''Sphenarpites'') does not have any keel. Ribs were single, but in some genera also bifurcating with shapes from sigmoidal to falcate. Sometimes, shell can have only striate ribs or is smooth (''Sphenarpites'' and older specimens of ''Eleganticeras'' and ''Ovaticeras''). Tubercules are rare. Dimorphism is known in some genera and it is observable mostly in size. Macrochons can be 4, to 6 times larger than microconchs. As an example, macroconchs of Pseudolioceras are more than 150mm in diameter, while adult microconchs are only 35-50mm. There are big size differences even within dimorphs. Specimens ca be 2, or sometimes even 3 times bigger than other specimens of same dimorph.〔 ==Genera== At least 10 genera is considered to be members of this subfamily.〔 This number can be increased, as some authors might consider valid some genera, which are by other authors considered to be synonyms of these 10. For example, ''Maconiceras'' is sometimes listed within this subfamily,〔Jérémie Bardin, Isabelle Rouget, Mohamed Benzaggagh, Franz Theodor Fürsich & Fabrizio Cecca (2015) Lower Toarcian (Jurassic) ammonites of the South Riffian ridges (Morocco): systematics and biostratigraphy, Journal of Systematic Palaeontology, 13:6, 471-501, DOI: 10.1080/14772019.2014.937204〕 while by other authors, it is considered to be a synonym of ''Harpoceras''.〔 * ''Cleviceras'' Howarth, 1992 * ''Eleganticeras'' Buckman, 1913 * ''Harpoceras'' Waagen, 1869 * ''Osperleioceras'' Krimholtz and Tazikhin, 1957 * ''Ovaticeras'' Buckman, 1918 * ''Polyplectus'' Buckman, 1890 * ''Pseudolioceras'' Buckman, 1889 * ''Sphenarpites'' Spath, 1936 * ''Taffertia'' Guex, 1973 * ''Tiltoniceras'' Buckman, 1913 Sometimes, more genera is referred to this subfamily, as some authors does not recognize validity of subfamily Protogrammoceratinae.〔 This would include genera: * ''Protogrammoceras'' Spath, 1913 * ''Fuciniceras'' Haas, 1913 * ''Lioceratoides'' Spath, 1919 * ''Neolioceratoides'' Cantaluppi, 1970 (sometimes considered to be a synonym of ''Lioceratoides''〔) In 1981 a new subfamily has been erected and named Polyplectinae, which is now considered to be a synonym of Harpoceratinae. Following genera were part of this subfamily:〔Venturi F, Bilotta M (2008) New data and hypotheses on early Jurassic ammonite phylogeny. Rev Paléobiol 27:859–901〕〔 * ''Polyplectus'' Buckman, 1890 * ''Praepolyplectus'' Venturi, 1981 (synonym of ''Polyplectus'') ==Distribution== Fossils of this subfamily have been found in the layers of upper Pliensbachian - lower Bajocian age. Distribution for subfamily is worldwide. All genera have been found in northern hemisphere, but only fossils of ''Harpoceras'', ''Osperleioceras'' and ''Polyplectus'' comes also from southern hemisphere.〔 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「Harpoceratinae」の詳細全文を読む スポンサード リンク
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