The paleohistological study of teeth and bones of the pycnodontid Neoproscinetes penalvai and bones of Tepexichthys aranguthyorum yields some specialized microstructural characteristics for these taxa. The stout molariform teeth of Neoproscinetes are inserted in deep alveolae constituted of spongy bone. The dentinous tissue is divided in a deep layer of orthodentine overlain by an external apical layer of durodentine (acrodine). The base of the teeth shows some folds in the pulp cavity that characterize a plicidentine-like organization of simplexodont type that can be attributed to the durophagous diet of the fish. In both species the bony tissues are constituted of cellular bone crossed by a lot of multiramified osteoblastic canalicles. Tepexichthys presents typical canalicles of Williamson although in Neoproscinetes these osteoblastic prolongations look slight different.