Current state of knowledge on Xenacanthiformes (Chondrichthyes, Elasmobranchii) from the Taquaral Member, Irati Formation, Permian of the Paraná Basin

Resumen

The Irati Formation, a Permian geological formation in the Paraná Basin, stands out for its remarkable geological and paleontological characteristics. Two members are currently recognized: the lower Taquaral Member and the upper Assistência Member. The lower portion, corresponding to the Taquaral Member, is predominantly composed of shales facies. At the base of this member, conglomeratic sandstones occur, characterized by a high concentration of vertebrate fossils. The sandy facies of the Taquaral Member is particularly well known for its abundance of Chondrichthyes remains. Xenacanthiformes constitute an extinct order of Chondrichthyes, with a fossil record ranging from the Carboniferous to the Late Triassic. Two families are currently recognized: Diplodoselachidae and Xenacanthidae, both present in the Irati Formation and represented by endemic genera and species. Diplodoselachidae is the most frequent family in the Taquaral Member, represented mainly by isolated teeth of Taquaralodus albuquerquei. This species, endemic to the Paraná and Parnaíba basins, is characterized by a well-developed principal cusp occupying a significant portion of the central and lateral regions of the tooth. Small teeth attributed to Xenacanthidae have also been recovered from the sandy facies of the Taquaral Member. Two distinct forms were identified: one belonging to the genus Xenacanthus and another assigned to an indeterminate Xenacanthidae.