Giant turtle fossil found in the state of Acre, Brazil

On its first expedition, a project funded by the Amazon+10 Initiative reveals clues about the Amazon millions of years ago.

By Bruna Bopp  |  Agência FAPESP – A rare and surprisingly well-preserved fossil of a giant turtle that lived between 10.8 and 8.5 million years ago, during the Miocene epoch, was found in the Boca dos Patos region of the municipality of Assis Brasil in the state of Acre, in the Brazilian Amazon.

The discovery was made by a research group led by professors and paleontologists Carlos D’Apolito Júnior from the Federal University of Acre (UFAC) and Annie Schmaltz Hsiou from the University of São Paulo (USP). They are the coordinators of the project “New Frontiers in the Fossil Record of the Southwestern Amazon”, which was funded through the Scientific Expeditions call for proposals. This call is part of the Amazon+10 Initiative, a program of the National Council of State Research Support Foundations (CONFAP). Funding came from the National Council for Scientific and Technological Development (CNPq), FAPESP, and the Acre State Research Support Foundation (FAPAC).

“We found the shell of the largest freshwater turtle that ever existed, Stupendemys geographicus,” says Hsiou, who has been studying the region for almost 20 years. The shell found was incomplete from the waist down and was very large, at about 1.70 meters wide. “We estimate that this shell, specifically, would have been almost 3 meters long. The shell is among the best preserved ever found of this species – a spectacular record of this super turtle that lived during the Miocene in the Brazilian Amazon.”

The diversity of fossils in the southwestern Amazon region has been known for over a century and a half, and the area has well-established fossil sites along the banks and ravines of its major rivers, especially in the state of Acre. “The problem is that we generally find very fragmented fossils,” explains D’Apolito Jr. “It’s common to find pieces of carapace, bone remains that are never or rarely found together, and mainly from smaller animals, which are easier to keep articulated. Finding large animals like this, well preserved, was a surprise. Now it’ll be possible to compare them with records from other places, such as Venezuela, which has more complete material from this species. We’ll finally be able to decipher whether it’s the same species or if there was a different one.”

The researcher compares the discovery to other large reptiles found in the region, such as Amazonian alligators. “It’s not exactly the same, of course, but in 1986, a complete skull of Purussaurus brasiliensis, a giant alligator, the largest that ever existed, was discovered. Based on this fossil, several studies were conducted to describe it, estimate its size, and determine its bite force. I consider it an excellent comparison, precisely because they’re reptiles that lived in the same region at the same time – a very different environmental period, warmer, with much more water available, where you’d find gigantic lakes and rivers.”

The Miocene epoch, which occurred between 23 and 5 million years ago, is known for its diverse aquatic and terrestrial fauna, and it was the origin of several Amazonian lineages. “Therefore, the deeper we delve into this geological interval, the more we’ll understand how biodiversity formed in the Amazon and how climate change caused extinctions and transformations in the region,” explains Hsiou.

Boca dos Patos Expedition

The fieldwork required significant logistical efforts. The team of 16 people, including ten researchers, five boatmen, and a cook, spent a full day traveling up and down the river to reach the excavation site. “The dry river is the main difficulty. We had to stop a lot to push the boat until we found a deeper spot and could navigate,” recalls D’Apolito Jr. The expedition was projected to last up to six days, because the return journey would be rendered even more difficult in case the waters dropped too low. “We were really lucky because this fossil was found on the first day,” celebrates the researcher.

Collecting the material took four days, including excavation, preparing the plaster jacket to preserve the shell, removal, and transporting it by boat to the city of Assis Brasil, which is about seven hours away – then on to the UFAC campus in Rio Branco, the state capital. “If we hadn’t found it in time, the material would have been lost for sure. When it rains and the dry riverbed floods, the water carries everything away. Nothing would have been left, much less in the preserved state in which we found the shell,” predicts the researcher.

The turtle was transported on a makeshift wooden base cut by the boatmen, who are primarily river dwellers and residents of Assis Brasil. Engaging with local communities is one of the project’s core principles. “The partnership with them is essential for us to discover new fossils and new species that have never been described before – or that only traditional and indigenous communities knew about. Now we can shed light on what really happened in proto-Amazonia and also understand the relationship between these peoples and fossils,” says Hsiou.

One of the project’s goals is precisely to connect with residents who have knowledge of fossil sites and have acted as sources, giving them and their communities recognition, as well as training on preserving regional paleontological heritage. “We already have some knowledge about the Upper Juruá River indigenous people’s understanding of fossils,” says the researcher. “We know how much respect they have for the fossils they find on the riverbanks. There’s a certain devotion to this material. Our intention is to further deepen environmental education and awareness of the importance of preserving both current and past biodiversity. They’re the guardians of these sites.”

During the expedition to the Boca dos Patos region, there was also contact with the local indigenous community of Aldeia dos Patos, the Manchineri people. “We went to ask for permission and show that we were there. We didn’t work on the indigenous land itself, but they went there to accompany our excavation work,” says D’Apolito Jr.

Next steps

The Stupendemys geographicus fossil was transported to UFAC in Rio Branco, where it will undergo scientific analysis and then become part of the university’s fossil collection. One of the guidelines of the Scientific Expeditions program, which funds the “New Frontiers in the Fossil Record of the Southwestern Amazon” project, is that material collected in the field be cataloged and registered with Amazonian institutions as a means of preserving local heritage.

“The UFAC collection has almost 10,000 fossils, and the vast majority were discovered nearby. By going to more remote places, we increase the chance of finding materials that don’t yet exist in the collection or that, although already known, are better preserved and provide more taxonomic information. This will give us a better understanding of what the Amazon was like in the past, how the fauna and flora evolved and adapted to climate change,” comments D’Apolito Jr.

The project aims to continue exploring other rivers in Acre and southern Amazonas, one of the main geological units within the Solimões Formation. “After this super turtle, we’re very hopeful we’ll find even more interesting fossils in these inhospitable and little-explored places,” says Hsiou.

She also highlights the importance of cooperation between institutions. “I’ve a strong partnership with researchers at UFAC. All of my projects funded by FAPESP, since my first Young Researcher [Research Grant], have focused on fossils from the Solimões Formation in the southwestern Brazilian Amazon or the Western Amazon,” she says. “We’ve already produced numerous scientific articles together and are very focused on training human resources, sharing research and materials, and also promoting exchanges between students from USP and UFAC,” celebrates the researcher.