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Hildoceratidae
Hildoceratidae is a family of Ammonoidea, ammonoid cephalopods from the Lower Jurassic, lower Pliensbachian (''Jamesoni'' zone) to lower Bajocian (maybe even upper Bajocian) substages, generally with strongly ribbed, involute shells. They are combined with the Hammatoceratidae (= Phymatoceratidae), Graphoceratidae, and Sonniniidae to make up the Hildoceratoidea. As many as seven subfamilies have been included in late 20th century, principle being the Arieticeratinae, Harpocertinae, Hildoceratinae, to which the Treatise, Part L, adds the Bouleiceratinae, Grammoceratinae, and Tmetoceratinae. Donovan et al. (1981) includes the same and adds the Leioceratinae which the older Treatise includes in the Graphoceratidae. Currently Leioceratinae are again members of Graphoceratidae and into Hildoceratidae are added newly established subfamily Leukadiellinae and Protogrammoceratinae, which has been by Donovan et al. (1981) considered as part of Harpoceratinae.M. K. Howarth 2013. Treatise on ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
