Ichthyoliths of the Corumbataí Formation: new occurrences and interpretations for São Paulo state, Brazil (northeastern Paraná basin)

Abstract

The Permian ichthyofauna of the Passa Dois Group is well known for the ubiquitous presence of disarticulated elements of a variety of fish taxa that remains largely understudied. Lower actinopterygians (Palaeonisciformes) are the most abundant, together with isolated teeth of Xenacanthiformes chondrichthians. This study brings new information on the external micro-ornamentations of actinopterygian teeth and rhomboid scales of the Corumbataí Formation collected for the first time in Santa Rosa de Viterbo region in the State of São Paulo, as well as a new proposition to approach this remains by using cluster analysis. These fossils were found in distal storm deposits (tempestite) and were separated from the rock matrix for analysis. Six distinct actinopterygian tooth morphotypes were identified. Curved forms are dominant in the assemblage, with ornamentations varying from smooth to ribbed shafts and others with grooves and tubercles. The scales are very fragmented showing surface micro-punctuations and longitudinal ridges. The Xenacanthiformes tricuspid teeth were very scarce in the assemblage and no complete specimen was recovered. Nonetheless, it was possible to identify them by their subtriangular shape and drop-shaped basal tubercle. Both ichthyodonts and scales show characteristics similar to at least other 26 occurrences, spread over more than 1000 km, and already described in the literature stratigraphically positioned above and below the Corumbataí Formation, attesting the wide temporal and spatial distribution of these fossils.