[Evolution of the pulp chamber and pseudodentin in the selachians the Brazilian coast (suborder Galeoidea)....

The author made a morphological study of Selachii (Suborder Galeoidae) of the Brazil coast using ground sections. Dental structures undergo modifications as one studies species of different evolutionary stages. The lower Selachii have an osteodentine nucleus which suffer alterations until it disappears leaving a pulp chamber in its place. The layer of pseudodentine shows modification too. It consists of pseudodentine in lower Selachii but its modifications are such that in higher Selachii (Sphyrnidae, for instance) one may suppose it is made of orthodentine. Based on these and other published data the author concludes that the degree of evolution of the pulp chamber and pseudodentine allows the establishment, with great probability, of the phylogenitic position of the Selachii within the Galeoidea Suborder.