Biometric analysis of the teeth of fossil and Recent hexanchid sharks and its taxonomic implications

摘要: A biometric analysis of the lower teeth Recent cow sharks (Hexanchidae) investigates ontogenetic and phylogenetic aspects dental characters employed by many ichthyologists palaeontologists. The currently used to separate two extant species sixgill (Hexanchus griseus H. nakamurai) are analysed fossil record their relatives reviewed. main results suggest that cusp number ratio (number cusps per mm) is preferable width tooth for inference total body size, at least in Hexanchus. presence a serrated edge or an enlarged acrocone appears depend on ontogeny care must be taken when using these as taxomomic characters. Three Eocene Hexanchus, collinsonae, hookeri, agassizi, new assemblage from late Ypresian/early Lutetian (Early/Middle Eocene) south-western France, also analysed. first may states agassizi. Hexanchus belonging vituliform lineage closely related living nakamurai, considered here only Lower Middle Eocene. brief overview Palaeogene suggests no evidence grisiform group (closely griseus) before Late