Research adds new pieces to the puzzle of the evolution of species

Fossil vestiges collected in the states of Maranhão, Paraná, and Rio Grande do Sul expand the knowledge regarding the species that inhabited these regions more than 200 million years ago.

By Noêmia Lopes

Agência FAPESP – The greatest episode of mass extinction in the history of the world occurred in the passage from the Permian (the period between 290 and 245 million years ago) to the Triassic (between 245 and 200 million years ago) Periods. The most widely accepted hypothesis is that volcanic events in Siberia altered the chemical composition of the atmosphere, resulting in climate change, alterations in the circulation of marine currents, and, ultimately, mass extinction.

In the quest for clues to better understand this key moment in geological history, Max Cardoso Langer, professor at Universidade de São Paulo’s (USP) Biology Department at its Ribeirão Preto Campus, performed field studies in the states that hold the main deposits of the Brazilian Permo-Triassic Period: Maranhão, Paraná, and Rio Grande do Sul.

Vertebrate, invertebrate, and even plant fossils from this period were found during two years of FAPESP-funded research, from 2010 to 2012.

The researchers found previously undiscovered flora in the rocks from the Permian Period in the Parnaíba Basin. “They bear a great similarity to Permian flora in Europe, the United States, and Southeast Asia. This is a very interesting technical detail because it shows that northern Brazil at that time had a biota that was more similar to regions in the northern part of the globe than the remainder of South America,” commented Langer.

Another discovery made in the Parnaíba Basin encompassed the period that the study addressed: on top of the Permian rocks, sediments from the Jurassic Age (from 200 to 145 million years ago) hid the cranium of a crocodyliform (a parent fossil of current reptiles). According to Langer, all tetrapods (four-legged animals) in Brazil from the Jurassic Period were known solely by their footprints, making this the first discovery based on a skeleton.

The third most significant finding from Maranhão consisted of fish vestiges from the semionotiform group from the Permian Period, animals that were approximately 25 centimeters long, with rough integuments because of a thick layer of scales. These fish had previously only been found in the Triassic Period and since.

“It was believed that these fish emerged after the great extinction. With the discovery, we see that, in reality, they belonged to a lineage that for some reason resisted the crisis event and dispersed afterward,” commented Langer. The material is at USP Ribeirão Preto for analysis by a partner-professor, Martha Richter, of the Natural History Museum of London.

Langer and his team went to the Serra do Cadeado in Paraná where there are also rocks from the Permian Period. The researchers found fish and amphibian fossils, which are currently being analyzed.

“We found vestiges of trilobites, which are arthropods – animals with articulated appendages and an exoskeleton – from marine environments. No one imagined that the sea had an influence on that region in the period in which these animals lived. But this is evidence that this connection existed,” said Langer.

The origin of dinosaurs 

The investigation of Triassic rock in the central depression of Rio Grande do Sul helped to describe three species of dinosaurs: one, a Pampadromaeus (Pampadromaeus barberenai), for the first time, whereas more complete and detailed descriptions were accomplished for the other two, a Guaibasaurus (Guaibassaurus candelariensis) and a Sacisaurus (Sacisaurus agudoensis).

“One of the aspects that make these discoveries so interesting are that the rocks from Rio Grande do Sul’s Triassic Period – similar to those of the Argentine Northeast – contain the oldest dinosaur fossils ever found in the world. That is, studying them is looking at the origin of these animals, looking at their first moments on Earth,” commented Langer.

Biotic dispersal in the period of the emergence of dinosaurs, after the extinction between the Permian and Triassic Periods, molded the patterns of the current biodiversity. It was the moment in which frogs, turtles, mammals, and the lines of bird, crocodiles, and lizards appeared. “New discoveries about dinosaurs always help to better explain how the fauna that we know today was structured,” affirmed Langer.

The research in Rio Grande do Sul also yielded descriptions of some new examples of tetrapods from the Triassic Period, such as the rhynchosaur Teyumbaita sulcognathus and the rauisuchian Decuriasuchus quartacolonia. The former was a low-lying elongated quadruped that was over two meters long and had a dental structure suited for vegetation, most likely seeds.

The rauisuchians were the top predators of the time, comparable, in terms of the food chain, to lions and tigers. “Some of them were over five meters long. They belonged to the crocodile family and lived with dinosaurs, which, in the beginning, were not as large and probably served as prey for rauisuchians,” explained Langer.

Olson’s hiatus

The project involved five lecturers and less than 15 students from partner institutions: Universidade Federal do Rio Grande do Sul (UFRGS), Universidade Federal de Santa Maria (UFSM), Universidade Luterana do Brasil (Ulbra), and Universidade Federal do Piauí (UFPI). The research efforts continue through the study of the collected material. Over the next two years, these efforts will allow researchers to uncover new relationships and fill the gaps in the documentation of fossil species. 

The knowledge obtained from the material can offer a unique contribution to the understanding the so-called Olson’s Hiatus, the period that extends from 270 to 265 million years ago (within the Permian) for which fossil findings are much more scarce.

“There is no known motive or accepted consensus for the scarcity. It could be solely the scarcity of rocks from this age,” said Langer. All the data recovered during the study are in the Lund System (www.lund.fc.unesp.br/lund), an online database for cataloguing fossils, the first of its kind in Brazil.

Langer had already scrutinized fossils from the Triassic Period in Rio Grande do Sul in his master’s project (1996) and doctorate (2001). In the ensuing years, he began to study deposits from the Permian Period in the states of São Paulo and Paraná. With the conclusion of the Permo-Triassic study, the researcher’s first step will be to continue adding the pieces of the evolutionary puzzle, which is now based on the study of specific fossils from the Triassic-Jurassic Period.