Rain can be a friend or foe for paleontologists. It can wash away soil or erode rocks, potentially revealing exciting fossils or crumbling already exposed, delicate specimens.

This is currently particularly true in the south of Brazil. In May, devastating floods in the state of Rio Grande do Sul uncovered bone pieces from at least 35 ancient animals, including a 233-million-year-old skeleton that is among the oldest dinosaur fossils in the world. But the rain showers and wet conditions that have occurred since then have prompted researchers to rush to recover other smaller, more vulnerable specimens that are also valuable.

The urgency is heightened by the unprecedented nature of the flooding. Between April 27 and May 27, the state's capital, Porto Alegre, recorded about 66 centimeters of rain - almost half of what it normally receives in a year. Many other cities in the state were also flooded. Some paleontological sites are still under water.

“If paleontologists are not there to collect material when it becomes visible, we risk that some of it will be lost forever,” says Leonardo Kerber, coordinator of the Quarta Colônia Paleontological Research Center (CAPPA) at the Federal University of Santa Maria in São João do Polêsine.

Exceed expectations

Since the May rains, paleontologist Rodrigo Temp Müller and his colleagues at CAPPA have intensified their monitoring of excavation sites near São João do Polêsine, about 280 kilometers west of Porto Alegre.

Eine Nahaufnahme eines Dinosaurierfossils

On May 15, about two weeks after heavy rains caused the banks of the Rio Grande do Sul river system to flood, Müller and the team discovered a 2.5-meter-long fossil of a carnivorous, bipedal dinosaur from the family Herrerasauridae. “We were sure we would find something after the heavy rain,” says Müller, but the specimen still exceeded expectations.

Herrerasaurids appeared and disappeared in the Triassic period (about 250 to 200 million years ago) and were the "first apex predators to appear among dinosaurs," says Aline Ghilardi, a paleontologist at the Federal University of Rio Grande do Norte in Natal, Brazil. They were replaced during the Jurassic period (200 to 145 million years ago) by larger dinosaurs called theropods, which include bipedal, three-toed carnivores such as Tyrannosaurus rex.

Some researchers argue that Herrerasaurids were the first theropods, but this classification is still controversial. “That’s why CAPPA’s discoveries are so important – they can help us clarify open questions like these,” says Ghilardi.

Work against the weather

But it was difficult to celebrate the discovery, says Müller. The floods have affected nearly 2.4 million people in Rio Grande do Sul, including 183 people who have died and 27 who are still missing, according to local authorities. “People living near the excavation site lost their homes,” he added.

Since their fossil discovery, Müller and his colleagues have taken rock and soil layers containing the Herrerasauridae specimen back to their laboratory to carefully extract the bones. So far, they've removed enough material to be cautiously excited: They think it could be the second most complete fossil of its kind ever found.

Eine Luftaufnahme von überfluteten Straßen in Porto Alegre

But the team can't relax yet. As intermittent rain continues, researchers are still rushing to save fossils of many small animals - animals that don't typically make headlines but are important nonetheless. “Everyone likes big dinosaurs,” says Kerber. But “the greatest biodiversity always lies with the smaller animals.” Such fossils help paleontologists reconstruct how species evolved and reveal details about the environments in which they lived.

Even the tiniest bones of animals, large or small, are a concern. They are the first to disappear when rain hits an excavation site, says Juan Cisneros, a paleontologist at the Federal University of Piauí in Teresina, Brazil. “They are rare and hard to find.” Ear bones of small reptiles, for example, can be only millimeters long, but they reveal a lot about an animal's brain and its possible intelligence.

Treasury

About a week ago, CAPPA researchers discovered the skull of a baby rhynchosaur - a parrot-billed, herbivorous reptile that averaged about 1 meter in length and dominated Earth in the Middle to Late Triassic (247 to 200 million years ago). Although these rhynchosaur fossils are numerous, Müller says, “they are important precisely because they are numerous.” In particular, they play a stratigraphic role in research as they mark Triassic sites, he adds. “Where there is a rhynchosaur, there will probably be a herrerasaur.”

The fossil-rich area where the paleontologists work is home to 29 excavation sites, 21 of which the CAPPA team has had access to since the floods, according to Müller and Kerber. Four are still practically completely submerged.

One advantage is that CAPPA is so close. “We don’t have to plan long trips; we can work in the field every week,” says Müller. The next challenge the researchers face is what to do with all the fossils they recover—the center doesn't have a museum. “It would be important to have one, not only to store the fossils we find,” says Kerber, “but also to educate the local population about how rich their region is.”