A new xenacanthid shark (Chondrichthyes) from the Teresina Formation, Permian of the Paraná Basin, southern Brazil

Abstract

The Kazanian/Tartarian Teresina Formation of the Parana Basin is so far the most productive stratigraphic unit in Brazil as far as Palaeozoic sharks are concern, although no articulate materials have yet been found. Teeth, fin spines and dermal scales are locally abundant, especially in hummocky deposits (tempestites). Biogeochemical evidence points to the fresh water origin of this fauna. New chondrichthyan teeth materials, coming from a single locality of this formation in the Municipality of Sao Gabriel in the State of Rio Grande do Sul are described and ascribed to a new xenacanthid shark, namely Wurdigneria obliterata gen. et sp nov. This new species bears tricuspid teeth where the central cusp is less than one third of the width and less than half of the height of the lateral cusps. Lateral cusps are lanceolate in cross section, round proximally, up straight in relation to the base and devoid of any serrations. The lateral cusps may bear a pair of vertical non-branching cristae. The base is round or sub-triangular in basal view and made up of osteodentine. The coronal button is inflated, usually round, or rarely, slightly flat at the pop. There are at least three large basal and lingual foramina. The basal tubercle is either larger, smaller or the same size as the length of the base of the lateral cusps. Histologically, the lateral cusps of Wurdigneria obliterata gen. et sp. nov. are made up of orthodentine externally and osteodentine obliterating the pulp canals. Enameloid tissue is absent. Judging from comparative dental anatomy, this was a predatory shark that could reach up to around 100 mm in length.