Abstract The so–called ‘triple–layered’ enameloid of neoselachian sharks is made of two main units: a superficial one and an internal one including the parallel–bundled enameloid and the tangled–bundled enameloid. The Triassic Synechodontiformes possess a parallel–bundled enameloid in which radial bundles are not very well–developed, contrary to what have been observed in more recent Synechodontiformes and other neoselachian sharks. The well–developed enameloid ridges that ornament the crown of many Synechodontiform sharks are superficial structures and show exactly the same organisation as in the cutting edges of more recent neoselachian sharks. We propose that two different mechanisms lead to the formation of ridges at the surface of the crown in neoselachian shark teeth. Ridges may result from an early mineralisation process during tooth development, or may mineralise near the end of the tooth development. Finally, on the basis of both tooth morphology and enameloid microstructure, the species “Hybodus” minor is transferred into the genus Rhomphaiodon.


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