In southeast Brazil, scientists studying the fossilized bones of giant dinosaurs have uncovered a deadly secret.
A group of sauropods—huge, long-necked dinosaurs that roamed the Earth about 80 million years ago—appear to have been struck down by a bone disease that likely contributed to their deaths.
The fossils, found in the municipality of Ibirá in São Paulo state, showed clear signs of osteomyelitis, a serious infection of the bone that can be caused by bacteria, viruses, fungi, or protozoa.
Researchers examined six different individuals from the same region and time period, and in each case, the disease appeared active at the time of death.
The bones showed no evidence of healing, meaning the dinosaurs probably died while still battling the infection.
The findings were recently published in The Anatomical Record.
Tito Aureliano, the study’s first author and a researcher at the Regional University of Cariri (URCA) in Ceará, explained why this discovery is so important. “There have been very few cases of infectious disease found in sauropods.
What makes this even more remarkable is that all of these bones come from the same site and time period, suggesting that the region created perfect conditions for pathogens to spread among these animals.”
The fossils analyzed were discovered between 2006 and 2023 at a site known as Vaca Morta. Some of the infected bones were ribs, while others came from the lower limbs of both small and giant sauropods.
Scientists used high-powered microscopes to examine the tissue and identified three previously unknown types of bone lesions linked to osteomyelitis.
Some of the marks looked like circular bumps, others resembled fingerprints, and a third set showed large, wide depressions. These lesions likely connected to the muscles and skin, creating open wounds that may have leaked blood or pus while the dinosaurs were alive.
Unlike injuries from predator bites, which often show signs of bone healing in the fossil record, these lesions offered no evidence of recovery.
The lack of regeneration suggested the disease was overwhelming and fatal. The researchers ruled out other conditions such as cancer, noting that the spongy texture of the infected bones—caused by increased blood vessels in the area—was unique to osteomyelitis.
This isn’t the first time the area has revealed evidence of infection. In 2021, another study reported the first known case of osteomyelitis in a small sauropod species called Ibirania parva. That infection was linked to a blood parasite. The two sets of findings suggest that the São José do Rio Preto Formation, a geological area where the fossils were found, was a hotspot for disease during the Cretaceous period.
At that time, the region had a harsh, arid climate with slow-moving rivers and stagnant pools. These conditions created environments where pathogens could thrive. Dinosaurs, turtles, and crocodile-like creatures all lived in the area, often getting trapped in the muddy waters. Scientists believe that mosquitoes or contaminated water may have carried infections from one animal to another, making it easy for diseases to spread among the population.
According to Aureliano, these new findings not only shed light on how disease may have contributed to the extinction of certain dinosaur groups but also provide valuable information for paleontologists.
By documenting different ways osteomyelitis appears in fossilized bones, scientists will be better able to identify infections in other ancient remains and distinguish them from unrelated conditions.
The study paints a vivid picture of life—and death—in prehistoric Brazil. While these dinosaurs faced many challenges, from predators to changing climates, it seems that even the microscopic world of disease played a deadly role in shaping their fate.
