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A set of bones belonging to sauropods, as long-necked dinosaurs are called, found in the municipality of Ibirá in the state of São Paulo, Brazil, reveals that the region was conducive to a bone disease that was fatal to these animals.

The researchers found signs of osteomyelitis, a bone disease that can be caused by bacteria, viruses, fungi, or protozoa, in the fossils of six individuals from the Cretaceous period, approximately 80 million years ago.

The bones show no signs of regeneration, suggesting that the animals died with the disease still active, probably as a result of it. The study was in the journal The Anatomical Record.

"There have been few findings of infectious diseases in sauropods, the first having been published recently. The bones we analyzed are very close to each other in time and from the same paleontological site, which suggests that the region provided conditions for pathogens to infect many individuals during that period," says Tito Aureliano, the first author of the study and a researcher at the Regional University of Cariri (URCA) in Crato, in the Brazilian state of Ceará.

One of the lesions was confined to the marrow. The other bones, which were also found between 2006 and 2023 at the Vaca Morta site, have lesions that extend from the marrow to the outer part. These lesions have a spongy texture, indicating vascularization in the region. This texture differentiates the lesions from other pathologies that can affect bone tissue, such as osteosarcoma and bone neoplasia, two types of cancer.

There were no signs of healing, which is when the bone tissue lost in the lesion is replaced by new tissue. This sign of regeneration is quite common in the fossil record of bones affected by bites from other dinosaurs.

Researchers analyzed the bones using a scanning electron microscope (SEM) and a stereomicroscope. Three previously unknown manifestations of osteomyelitis were identified in the fossils. One set contained small protrusions, bone elevations, or "bumps" in a circular shape.

Other protrusions had a pattern similar to fingerprints and were elliptical in shape. Finally, a third set had round, wide marks that were larger than all the others. "These lesions could connect with muscles and skin and become exposed, oozing blood or pus," explains Aureliano.

It was impossible to determine exactly which bones were analyzed; however, it was known that one was a rib and the rest were from the lower limbs of small and giant species. It was also not possible to identify the cause of the infections.

In a 2021 study published in , researchers described the first case of bone infection caused by a blood parasite resulting in osteomyelitis. The bones in that case were from a small sauropod species, Ibirania parva, which was found in the same location as the fossils analyzed now.

The region, known as the São José do Rio Preto Formation—because it encompasses the municipality of the same name—had an arid climate with shallow, slow-moving rivers and large pools of standing water. In these environments, many dinosaurs became stuck and died, producing fossils.

"This environment probably favored pathogens, which may have been transmitted by mosquitoes or by the water itself that was ingested by the fauna, which included dinosaurs, turtles, and animals similar to today's crocodiles," says Aureliano.

The author also points out that the evidence provided by the study may be useful for future paleontological and archaeological work because it presents different manifestations of the same disease in bones and differentiates it from others.