The morphology and histology of the scales of the Cretaceous gar Obaichthys (Actinopterygii, Lepisosteidae): phylogenetic implications

Scales of the lepisosteid fish dagger Obaichthys decoratus and dagger O.? l aevis, from the Lower Cretaceous of the Araripe Plateau (Northeast Brazil) resemble those of palaeoniscoid-type, in which a ganoine layer overlies a d entin layer located above a basal plate composed of lamellar bone. However, the presence of canaliculi of Williamson in these scales confirms that dag ger Obaichthys is a typical neopterygian. The scales of dagger Obaichthys d iffer from those of other gars, which do not have a dentin layer and that h ave ganoin tubercles with characteristic size and density. Our observations support the plesiomorphic status of dagger Obaichthys within the Lepisoste idae, and confirm the validity of the two species: dagger O. decoratus and dagger O.? laevis. (C) 2000 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.