A comprehensive comparative study of the dental morphology of extant heterodontid sharks has led to new information, placed in Part I. Complementary to Reif’s classic (1976) study, extensive investigation of the dental morphology of the nine species of Heterodontus reveals their exclusive ontogenetic heterodonty. This dental morphology appears to separate Heterodontus into two different morphotypes, one group including the species H. japonicus, H. portusjacksoni and H. zebra and the other H. francisci, H. galeatus, H. mexicanus, H. omanensis, H. quoyi and H. ramalheira.
Within these morphotypes a specific distinction is not possible, as is demonstrated by the ontogenetic study. As far as available, the tooth morphology of ontogenetic series is described and illustrated based on isolated teeth as well as on jaw sets of each species, depending on their availability. Information about the locking mechanism of the teeth and a terminology of the Heterodontus attributes is given. All Jurassic, Cretaceous, Paleocene, Eocene, Oligocene, Miocene and Pliocene nominal species referred to the family Heterodontidae in the literature are re-described and re-illustrated as far as possible in Part II; subsequently they are compared with the various types of ontogenetic heterodonty in the extant taxa of both morphotypes. Fossil species are grouped stratigraphically in ascending order into one of two Heterodontus morphotypes. A phylogenetic analysis and scheme are given illustrating the new approach to heterodontid relationships based on the new dental morphological data.