Brasilestes stardusti is the name of the oldest known mammal of Brazil. She lived at the end of the Mesozoic between 87 million and 70 million years in today's northwestern state of São Paulo. It is the only Brazilian mammal that has coexisted with the dinosaurs.
The discovery of Brasilestes was announced on May 30, 2018 by a team led by Max Langer, a professor at the Faculty of Philosophy, Science and Literature at the University of São Paulo (FFCLRP-USP). Langer's team consisted of colleagues at the Federal University of Goiás and the University of Campinas in Brazil, the La Plata Museum in Argentina, and the Massachusetts Institute of Technology (MIT) in the US.
Physically Brasilestes consists of a fossilized premolar with a maximum crown length of 3.5 mm. "The tooth is small and incomplete: the roots are missing," said paleontologist Mariela Cordeiro de Castro, first author of the recent work published in Royal Society Open Science "Small but not Tiny." Castro continued. "Although the Brasilestes tooth is only 3.5mm in size, it is three times larger than any known Mesozoic mammal teeth In the era of dinosaurs, most mammals were as big as mice, Brasilestes was much larger, about the size of an opossum. " 19659005] The name of the new species pays homage to British rock star David Bowie, who died in January 2016, a month after the fossil was found. Brasilestes stardusti alludes to Ziggy Stardust, an alien character created by Bowie for a 1972 album.
The research was funded by the São Paulo Research Foundation-FAPESP as part of the thematic project "The Origins and Rise of Dinosaurs in Gondwana (late Triassic-early Jurassic), for which Langer is Principal Investigator.
The Fossilized Tooth located in a promontory of the Adamantina Formation in General Salgado, São Paulo State, located on a field on a ranch called Fazenda Buriti.
"We visited Mesozoic outcrops, as Júlio Marsola [another member of the team] discerning as a lynx, discovered a small tooth sticking out of a rock, "said Castro, a professor at the Federal University of Goiás (UFG).
" The general Salgado deposits are known. Several Mesozoic crocodiles are from them. The particular glimpse of where I found Brasilestes is interesting, with dozens of fragments of the Mesozoic I stooped to take a closer look at a small portion of the digestion to see if there were egg shells and discovered the tooth. If he had stayed outdoors for a few more days, the rain would have blown
"When I noticed what seemed like the base of the two roots of the tooth [the roots themselves have broken off] I thought it must be a mammal the certainty that it is indeed a mammal. "
A placental mammal in the Botucatu Desert
While a 3.5 mm large, especially incomplete tooth seems inadequate In fact, extinct mammals are often described on the basis of a single fossilized tooth.
This is the case because teeth are the most durable part of the mammalian skeleton While many live animals and reptiles, for example, constantly grow new teeth throughout their lives, mammalian teeth are often the only skeletal remains left intact long enough to petrify. 19659005] The fact that only a single premolar of Brasilestes remains and is incomplete has prevented the researchers from distinguishing with certainty the group of mammals to which the species belongs. The tooth belonged to a therian, a member of a large Subclass of mammalia, which includes marsupials and placentals.
Although there is insufficient evidence to support the inclusion of Brasilestes in both infra classes, the researchers believe (but can not categorically conclude) was a placental mammal. If this is the case, the fossil is unique.
Today there are three main groups of mammals, namely placentals, marsupials and monotremes. All three developed during the Mesozoic. By that time, however, they were by no means the only mammal groups. There were also multituberkulates that were common in the northern hemisphere, as well as groups typical of the southern hemisphere, such as Meridiolestide and Gondwanatherians – named after Gondwana, the ancient southern supercontinent, Africa, South America, Australia, Antarctica and India
] The earliest Mesozoic mammalian fossils were found in Argentine Patagonia in the early 1980s, and now about 30 species are known. Until the announcement of Brasilestes, these were the only ones found in South America. No one remotely resembles the little tooth found in Brazil.
"When I showed the Brazilian fossil to palaeontologist Edgardo Ortiz-Jaureguizar at the Museum of La Plata, he was very surprised, saying that he had never seen anything like this before, immediately showing it to another specialist at the same facility, Francisco Goin, who had the same reaction, said that Brasilestes did not resemble any other Mesozoic mammal found in Argentina, hence South America, "recalled Castro.
Among the 30-odd Argentine species of Mesozoic mammals, there are meridiol esters, gondwanatherians and even some suspicious mulituberkulate. There are no marsupials or placentals. The only fossils in these two groups found in South America come from the mass extinction that extinguished the dinosaurs 66 million years ago in an event marking the end of the Mesozoic and the onset of the present geological era, the Cenozoic In Brazil, there were only traces of Mesozoic mammals to discover Brasilestes, hundreds of traces and traces left by unknown creatures 130 million years ago as they crossed the dunes of the Botucatu Desert in what is now the state of São Paulo. The solidified surface of these dunes has been preserved as sandstone slabs on which the footprints can be seen.
In 1993, Reinaldo José Bertini, a professor at the University of São Paulo (UNESP) in Rio Claro, announced the discovery of a mammalian jawbone fragment with a single tooth much smaller than the Brasilestes premolar. However, Bertini did not publish a detailed study of the fossil and therefore could not name a new species.
"Brasilestes is not only the first mammal described in the Brazilian Mesozoic, but also one of the few Mesozoic mammals in more central regions. The Argentine fossils were found in geological formations in Patagonia, the southern tip of the continent," said Langer.
"Moreover, Brasilestes is different from anything that was found millions of years ago and 70 million years ago," says the FAPESP Project Coordinator.
New species possibly related to a mammal from India
Even more surprising is the mesozoic mammal with premolars most similar to the Brasilestes tooth lived on the other side of the world, in India , between 70 million and 66 million years. His name is Deccanolestes. No other creature in the global fossil record is so similar to Brasilestes
How could two members of the same lineage live so far apart in unconnected regions? About 100 million years ago, when South America and Africa had just been separated by the opening of the South Atlantic, India detached itself from Gondwana and began to wander the Indian Ocean.
This means that at least 100 million years have passed before the ancestors of Brasilestes and Deccanolestes populated the supercontinent Gondwana. In other words, the lineage that includes Brasilestes and Deccanolestes is much older than the age of their fossils – between 87 million and 70 million years for Brasilestes and between 70 million and 66 million for deccanolestes.
"The discovery of Brasilestes raises much more questions than the question of the biogeography of mammals in the South American Mesozoic," Langer said. "Thanks to Brasilestes, we have realized that the story of Gondwana's mammals is more complex than we thought."
Finding triggers speculating on the origins of Xenarthrans
This could lead to new hypotheses and new lines of investigation. Who knows, for example, whether future research inspired by the discovery of Brasilestes will reveal the origins of a typical South American group, Xenarthrans, armadillo, anteater and sloth? Castro's main research interest is the evolutionary history of xenarthrans.
"An interesting feature of the Brazilestes premolar is its only 20 microns thick, super-thin enamel." The Brasilestes enamel is the thinnest of all Cretaceous mammals. Most Mesozoic mammals have enamel in the range of 100 to 300 microns, "said Castro.
"Ten known species of xenarthrans are now alive, hundreds are extinct, only three have enamel." The microstructure of Brasilestes "The premolar enamel is very similar to that of the nine-band armadillo," said the FAPESP -supported researchers.
According to Castro, "molecular clock evidence suggests that the xenarthran line began at least 85 million years ago, although the oldest armadillo fossil found in Rio de Janeiro is about 50 million years old."  While it's fascinating to think of Brasilestes as an ancient xenarthran, it's too early for such confirmation.
"The age and origin of Brasilestes are consistent with the molecular hypotheses for the origin of xenarthrans, but it would be premature to deduce taxonomic affinity for the morphological differences between the Brasilestes tooth and the armadilloid teeth," says Langer.
"We have only one Brasilestes fossil, which is far from enough to draw conclusions from the fossil," he said.
The fact that no Mesozoic mammalian fossils were found in Brazil off Brazil could mean that such fossils are rare or too fragile. "Who knows, maybe one day we'll find new Brasilestes fossils to help us better understand his story – it could take decades," Langer said.
Utah fossil indicates global exodus of mammalian close relatives to the major continents
Mariela C. Castro et al., A Late Circular Mammal from Brazil and the First Age of Radioisotopia for the Bauru Group, Royal Society Open Science (2018). DOI: 10.1098 / rsos.180482