Harpoceratinae
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 9 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 9. For example, "Maconiceras" is sometimes listed within this subfamily, while by other authors, it is considered to be a synonym of "Harpoceras". Sometimes, more genera is referred to this subfamily, as some authors does not recognize validity of subfamily Protogrammoceratinae. "Neolioceratoides", which has been included within Protogrammoceratinae and was also considered to be a synonym of  Lioceratoides is now member of Hildoceratinae, which is reason why it is not listed below. This would include genera: In 1981 a new subfamily has been erected and named Polyplectinae, which is sometimes considered to be a synonym of Harpoceratinae, but sometimes it is still used as valid taxa. Following genera are part of this subfamily: 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. Timeline  and evolution. If Protogrammoceratinae shall be considered a valid subfamily, then Harpoceratinae might be of polyphyletic origin with at least 2 main lineages, both evolving from Protogrammoceratinae. First one started in upper Pliensbachian (Spinatum zone) when "Tiltoniceras" evolved from "Lioceratoides", or "Protogrammoceras". In Toarcian, during lower part of Exaratum subzone of Falciferum zone it evolved into "Eleganticeras", which soon gave rise to "Cleviceras". "Polyplectus" evolved from this genera. Second lineage originated from "Protogrammoceras", which has been predecessor for "Harpoceras". Three genera evolved from this genus - "Osperleioceras" (from "Harpoceras subplanatum"), "Ovaticeras" (from "Harpoceras falciferrum") and "Pseudolioceras" (probably also from "Harpoceras falciferrum ). Pseudolioceras" is the only known member of this subfamily that lived also in middle Jurassic. Last common ancestor of both these lineages might have been "Protogrammoceras" that lived in Spinatum zone of Pliensbachian or sooner. Some authors (Knyazev et al., 2007) does not recognize validity of "Cleviceras" and place its species still in "Harpoceras", while they considers "Harpoceras falciferrum" to be descended from "Harpoceras exaratum" (in most of recent literature is this species member of genus "Cleviceras"). Origin of the remaining 2 genera is probably unknown. "Taffertia" lived in Falciferrum zone of early Toarcian (maybe only in Exaratum subzone). "Sphenarpites  is known from single specimen that comes from early Toarcian.