A conical, horn-shaped bone found during 1978 in the Santana Formation (Aptian) of the Chapada do Araripe (Ceará), famous because of its very abundant ichthyo-fauna, is preliminarily described. The bone is tentatively classified as an ischium belonging to an Ornithischia, Ornithopoda, perhaps within the lines which led, during the Middle Cretaceous, to the quadruped orders Ceratopsia or Ankylosauria. The specimen would prove to be the sole occurence up today of ornithischians skeletal remains in Brasil, these reptiles having been already recorded in this country on the basis of trackways, as well as one among the very few found in South America.
