“Aline, could this be a microfossil?”

The question popped up on Aline Ghilardi’s phone via a text from her husband, fellow paleontologist Tito Aureliano, while she was studying for a test that would make her a professor at the Federal University of Rio Grande do Norte in Brazil.

It was 2018, and Aureliano was examining the fossilized leg bone of a small dinosaur from the titanosaur family discovered by Ghilardi 12 years earlier. An expert in fossilized dinosaur tissue, Aureliano had been tasked with looking more closely at the spongey lumps on the bone’s surface.

The pair of paleontologists had already made a fascinating discovery—that the dinosaur, which lived more than 80 million years ago during the Cretaceous period, had an acute bone infection called osteomyelitis. But Aureliano prepared thin slices of the fossilized bone to allow for a more detailed study of the infection, which still affects animals and humans today.

What he found when he looked through his microscope were microfossils, fossilized microorganisms generally less than a millimeter in size. Although microfossils can be plants or animals, this time they were parasites. The discovery left him so shocked that he knew he had to send a photo of the discovery to his wife right away.

“When I looked at the photo my chin dropped all the way to the ground,” says Ghilardi. “I said, ‘Tito, nobody has ever found anything like this before. I don’t even know what to do. I don’t even know what to say. We need to call in more people.’”

The team of experts they assembled confirmed what Aureliano suspected: There were microfossils in the bone. The discovery was exceptional; it was indeed the first time fossilized parasites had been found in a dinosaur bone. The paleontologists published their findings in Cretaceous Research in October.

Both the dinosaur—a small, long-necked titanosaur sauropod about sixteen feet from nose to tail—and the 70 blood parasites found within the vascular channels of its bone are newly discovered species that have yet to be named or described.

Ghilardi had unearthed the bone in 2006 at a dig site in the state of São Paulo, and as soon as she saw the lesions on its surface, she knew she wanted to investigate further. None of the other fossils found there had this type of damage, and initially she thought it might have been caused by one of the forms of bone cancer being investigated by other paleontologists.

Usually, pre-historic illnesses are diagnosed in fossils by the naked eye or simple x-rays. The high costs of using microscopic equipment like CT scans puts the more detailed picture they would provide out of reach for most research teams. That’s why Ghilardi and Aureliano turned to colleagues at the University of São Paulo’s School of Medicine for help. There, they were able to do a CT scan of the bone. It was the first time a 3-D model had ever been created of a fossil with this type of pathology.

With the image, the researchers were able to diagnose the mystery lesions not as cancer, but as osteomyelitis. They could also see that the infection extended from deep within the bone all the way to its surface, likely causing the elderly dinosaur a lot of pain and creating inflammation on its bones and open sores on its skin. Due to the gruesome nature of the injuries, the team nicknamed the creature “Zombie Dino.”

As they prepared their article , Ghilardi and Aureliano noticed a lack of histological data on osteomyelitis, even in research related to modern medicine. The infection is most commonly caused by severe trauma where both the bone and the skin break, allowing bacteria to enter the bone more easily. Osteomyelitis is a frequent concern during orthopedic surgery on humans.

“We saw in the scientific literature that this [decision to extract tissue samples] had only been done with one dinosaur before,” says Aureliano. “And we also saw that there was a really big demand in the world of science to understand how this [osteomyelitis] happens. So, we wanted to know how, at the microscopic level, the tissue was being remodeled because of the infection.”

Aureliano thought preparing thin tissue samples could help others further study osteomyelitis for purposes beyond just paleontology.

“The body’s mechanisms of defense are still not 100 percent understood,” says Marcus Vinícius Guimarães de Lacerda, an infectologist at the Dr. Heitor Vieira Dourado Tropical Medicine Foundation who was not involved in the research. “This [study] could help us understand the inflammation’s mechanisms over time and how these mechanisms evolved.”

It was when they cut into the fossil to prepare the samples that Aureliano and colleague Fresia Ricardi Branco, a geologist and professor of paleontology at Campinas State University in Brazil, saw the microfossils, originally a set of ten, for the first time. Stunned, they then called on paleoparasitologist Carolina Nascimento, of São Carlos Federal University, to take a closer look.

Nascimento was able to identify dozens more, over 70 in total, of the preserved microorganisms, which ended up being blood parasites. Before that moment, fossilized parasites had only ever been found in amber or fossilized feces.

But one thing the team has yet to figure out is whether the parasites caused the osteomyelitis, or whether the infection created an ideal environment that allowed the parasites to take advantage of the dinosaur, enter its bones and thrive. With no signs of a break or a bite in the bone, the researchers have been left stumped as to how the infection started.

Now, Ghilardi and Nascimento are looking more closely at the parasites to try to find answers. They know the only reason they were able to understand the discoveries they already made was teamwork across paleontological specialties, including pathology, histology and parasitology. They hope continuing to work together will lead to results that show their research can help with the advancement of other areas, like medicine, too.

Understanding the evolutionary paths of disease Ghilardi says, is crucial, particularly when it involves parasites. Knowing how osteomyelitis affected pre-historic animals, like dinosaurs, and how it changed before infecting animals and humans today, could be the key to finding a way to combat it now.

“It could give us a clue,” she says, “as to where to look for a cure.”