An ancient paleopolar ray-finned fish from the south of Brazil sheds light on the early history of the group
When considering Brazil, or even South America as a whole, many envision a tropical environment, with a diverse fauna and flora compared to temperate regions like Europe and North America. However, that has not always been the case. During the Paleozoic (~540–251 million years ago) the situation was reversed: most of South America was close to the Antarctic circle while Europe and North America occupied the tropics. Now imagine if there were large predatory bony fishes roaming the seas around what is now South America around 380 million years ago, despite the harsh polar environment.
In a paper published in Biology Letters, UMMP and Michigan EARTH graduate student Rodrigo Tinoco Figueroa, together with UMMP director and EARTH professor Matt Friedman, and Luiz Carlos Weinschütz from the Universidade do Contestado, Santa Catarina, Brazil, report a new species of fossil fish, named Austelliscus ferox from the State of Paraná, Brazil. Likely dating to the Devonian (~380 million years ago), this fossil represents the oldest occurrence of a ray-finned fish in the circumpolar region. Even more remarkable is the similarity between Austelliscus and a younger Tegeolepis, a fish that lived close to the end of the Devonian in North America. Both these fishes would have been large predatory animals, as indicated by the enlarged fangs near the front of their mandibles.
The Devonian fauna of South America is distinctive. It contained a high number of endemic species (those found nowhere else) during the early parts of the Devonian, but became more similar to the Northern Hemisphere fauna by the later part of the period. This early, unique assemblage–-the so called Malvinokaffric realm–-is poor in vertebrate remains. Fragments of placoderms and sharks have been known for more than 100 years, beginning with discoveries by the Geological Commission of the Brazilian Empire in the late 19th century. These already demonstrated a clear contrast with faunas of northern South America as well as those of North America and Europe, where sharks and placoderms shared aquatic environments with diverse bony fish lineages. Thus, it is possible to infer that the peculiarity of Malvinokaffric fauna was not restricted to invertebrates.
The discovery of a ray finned fish in the Devonian of southern Brazil not only adds to the Malvinokaffric vertebrate fauna, but also provides clues about the early diversification of ray-finned fishes. The age and morphology of Austelliscus could indicate that the important events in the diversification of ray finned fishes happened outside of the species-rich paleoequatorial localities of North America, Europe and Asia. This discovery, along with other important fossil discoveries of the last few years, highlights the importance of exploring poorly sampled regions that were at high latitudes during the Devonian. These sites could help improve our understanding of the patterns of diversification and distribution of several early vertebrate lineages.
Summary written by author Rodrigo Tinoco Figueroa