Fossils lay about eight meters below the surface. Workers first uncovered them during environmental monitoring tied to the construction project's licensing process. Archaeologists initially mistook the bones for remains of large prehistoric mammals that may have lived alongside ancient humans.

Who recognized the find?

Elver Luiz Mayer, a professor at the Federal University of the São Francisco Valley, became involved in 2021. He typically studies mammals from the much more recent Quaternary period.

"Given its depth of about eight meters, I realized that it was much older. The age of the geological formation was already known from previous research and indicated that it was material from the transition from the Lower to the Upper Cretaceous, about 120 million years ago," Mayer said.

He then assembled a multidisciplinary team to study the specimen. Crews prepared the fossils extensively in the state of Pará before returning them to Maranhão. The bones now reside at the State Center for Natural History and Archaeology Research in São Luís.

What does bone microstructure reveal about its growth?

A separate analysis, led by Tito Aureliano and Aline Ghilardi of the Federal University of Rio Grande do Norte, examined thin sections of the dinosaur's bones under a microscope. The growth pattern mixes features seen in older sauropods with traits typical of titanosaurs, a group closely related to Dasosaurus.

The combined pattern suggests that certain bone remodeling processes may have evolved earlier in the sauropod lineage than scientists previously thought. That could help explain how some members of the group reached truly enormous body sizes.

Why does a construction site matter to paleontology?

Brazil's dense vegetation makes traditional fossil hunting difficult. Large building projects, highways, and quarries often expose rock layers that researchers could not reach on their own.

"Brazil is a tropical country with dense vegetation. Geologists and paleontologists rely heavily on human activity to excavate, expose the rocks, and reveal the fossils," Langer said.

"If we map Brazil's fossil sites, we'll see highways and quarries," he added. "These projects are important for understanding our heritage. But it's obvious that specialized monitoring and artifact recovery are necessary, which doesn't always happen."

Mayer added that closer cooperation between builders and paleontologists would help protect fossil deposits while supporting new discoveries.

What happens next?

The research team is negotiating with the construction company for permission to return to the Davinópolis site. Additional bones could refine the picture of Dasosaurus tocantinensis and the larger dinosaur group to which it belonged.

The species name honors the dense forests of Maranhão, which early Portuguese colonizers called a "maranhão" tangle, and the Tocantins River, whose waters run near the fossil site.

The study received support from the São Paulo Research Foundation (FAPESP) through a doctoral scholarship, a postdoctoral fellowship, and a Young Investigator grant.