After the dinosaurs died out 66 million years ago, Earth’s animal life forms went in unique directions in some parts of the globe. In South America, which had separated from Africa and was not yet connected to North America, an order of placental mammals arose; nearly all of this order, the Xenarthra, are extinct today, with the exception of modern armadillos, sloths, and anteaters. This was also where the first “terror birds” appeared, the popular name for giant carnivores who also went extinct, flightless birds which belonged to the family Phorusrhacidae. Examples of this ancient South American fauna that lived between 42 and 39 million years ago—a period which up to this point had left no vertebrate fossil records in Brazil—were discovered in a new paleontological site in the state of Paraná.
On a rocky outcropping of the Guabirotuba geological formation on the border between the cities of Curitiba and Araucária, a team coordinated by researchers at the Federal University of Paraná (UFPR) and the Western Paraná State University (UNIOESTE) found teeth and bone fragments from 10 distinct types of placentary mammals: seven had shells, ancestors of the extinct glyptodonts and present-day armadillos, and three had hooves and were technically ungulates. Among the marsupials, mammals with a pouch to carry their young, traces of three extinct genera were found, including sparassodonta, carnivorous predators that had large canine teeth and reached the size of a leopard.
Most of the Guabirotuba fauna resemble or are identical to the mammal fossils found in the province of Chubut, in Argentinean Patagonia, which lived during the geological era known as Barrancan age, between 42 and 39 million years ago. But a previously unknown species of armadillo, Proeocoleophorus carlinii, was described in the scientific paper that presented the findings in Paraná, published this year in the Journal of Mammalian Evolution. The researchers recovered a large amount of fossilized plates that made up the shell of the animal. “We started studying the new site through the mammals, because some of these fossils occur only in the Barrancan period and act as evidence for geological dating,” says paleontologist Fernando Sedor, scientific coordinator of the Museum of Natural Sciences at UFPR and lead author of the study.
This is the case of the remains of the primitive armadillo in the genus Utaetus and the sparassodonta from the genus Nemolestes, both found in the capital of Paraná. “In future work, we should be able to describe at least two new extinct species of marsupials,” says paleontologist Eliseu Vieira Dias, professor at UNIOESTE in Cascavel. In addition to mammals, the Curitiba site still has fossils of fish, amphibians, turtles, crocodylomorpha, mollusks, a “terror bird,” and tracks and marks left on the rocks by invertebrates. The first fossils from the Guabirotuba formation were found in 2010 by the geologists Antonio Liccardo, from the State University of Ponta Grossa (UEPG), and Luiz Carlos Weinschütz of Contestado University (UNC) in Santa Catarina, who found a crocodylomorpha tooth there. Later, Sedor and Dias began systematic studies at the site that led to a broader set of fossils.
New primitive armadillo
Besides Guabirotuba, there are only four other geological formations in Brazil known to have vertebrate Paleogene fossils, from the geological period between 66 and 23 million years ago: Maria Farinha, in Pernambuco, with materials from between 66 and 56 million years ago; Itaboraí, in Rio de Janeiro (56 to 48 million years); Entre-Córregos, in Minas Gerais (35 to 30 million years); and Tremembé, in the Taubaté basin in São Paulo (28 to 16 million years). But only remains of mammals from the Paleogene period were found in Itaboraí and Tremembé. Consequently, in chronological terms, the Curitiba fossils represent an intermediate age with regard to the extinct fauna found in these two formations. “The mammals at Guabirotuba are slightly younger than those at Itaboraí and a bit older than those from Tremembé,” states Sedor. “They are extremely important for understanding the evolution of some mammal lineages in South America.”
The new species of mammal in the Xenarthra superorder discovered in Paraná was named Proeocoleophorus carlinii because it appears to be an older, earlier form of Eocoleophorus, an extinct genus of primitive armadillo originally found in the Taubaté region. Sedor and Dias hope to identify other similar cases when they compare fossils from the Itaboraí, Tremembé, and Guabirotuba formations, which are located in basins in the southeast of the country that resulted from the so-called southeastern Brazil continental rift. This rupture generated a number of faults that produced a set of valleys approximately 100 kilometers (km) wide that stretch for nearly 1000 km from the coast of Paraná to Rio de Janeiro, passing through Curitiba and São Paulo.
The comparative studies of the vertebrates will not be limited to mammals. In partnership with colleagues from Paraná, the paleontologist Herculano Alvarenga, founder and director of the Natural History Museum of Taubaté, will examine the fossils of the “terror bird” found in Curitiba. “They really found a Phorusrhacidae,” explains Alvarenga, a specialist in bird fossils. “It is smaller than our Paraphysornis, but it might be the first specimen of a ‘terror bird’ that lived during the Eocene [an epoch between 55 and 36 million years ago].” The paleontologist discovered a nearly complete skeleton of Paraphysornis and described the species, a 2-meter-tall predator that terrorized the Paraíba valley with its hook-shaped beak 23 million years ago.
SEDOR. F. A. et al. A new South American paleogene land mammal fauna, Guabirotuba formation (Southern Brazil). Journal of Mammalian Evolution. V. 24, No. 1, p. 39-55. Mar. 2017.