title: A new Xenacanthiformes shark (Chondrichthyes, Elasmobranchii) from the Late Paleozoic Rio do Rasto Formation (Paraná Basin), Southern Brazil.
abstract: The Brazilian records on Xenacanthiformes include teeth and cephalic spines from the Parnaíba, Amazonas and Paraná basins. This work describes a new species of Xenacanthidae, collected in an outcrop of Serrinha Member of Rio do Rasto Formation (Wordian to Wuchiapingian), Paraná Basin, municipality of Jacarezinho, State of Paraná. The teeth of the new species are two or three-cuspidated and the aboral surface show a smooth concavity and one rounded basal tubercle. The coronal surface presents one semi-spherical and subcircular coronal button, and also two lateral main cusps and one central (when present) with less than one fifth of the size of the lateral cusps in the labial portion. The lateral cusps are asymmetric or symmetric, rounded in transversal section, lanceolate in longitudinal section, devoid of lateral carinae and lateral serrations, and with few smooth cristae of enameloid. In optical microscope the teeth show a trabecular dentine (osteodentine) base, while the cusps are composed by orthodentine, and the pulp cavities are non-obliterated by trabecular dentine. The fossil assemblage in the same stratigraphical level and in the whole Rio do Rasto Formation indicates another freshwater record for xenacanthid sharks.
authors.affiliation: Instituto de Geociencias, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brasil.
authors.forename: Victor E
authors.initials: VE
authors.lastname: Pauliv
authors.affiliation: Laboratorio de Geologia e Paleontologia, Centro de Ciencias Biologicas e da Saude, Universidade Estadual do Oeste do Parana, Cascavel, PR, Brasil.
authors.forename: Eliseu V
authors.initials: EV
authors.lastname: Dias
authors.affiliation: Setor de Ciencias Biologicas, Museu de Ciencias Naturais, Centro Politicnico, Universidade Federal do Parana, Curitiba, PR, Brasil.
authors.forename: Fernando A
authors.initials: FA
authors.lastname: Sedor
authors.affiliation: Museu de Ciencias Naturais, Fundacao Zoobotanica do Rio Grande do Sul, Porto Alegre, RS, Brasil.
authors.forename: Ana Maria
authors.initials: AM
authors.lastname: Ribeiro
mesh_terms: D000818:Animals; D001938:Brazil; D005580:Fossils; D019015:Geologic Sediments; D010163:Paleontology; D012754:Sharks / Q000145:classification*