Scientists from Canada's Royal Ontario Museum and McMaster University say they have identified malignant bone cancer in a dinosaur for the first time.
The new research was published earlier this week in the journal The Lancet Oncology.
The diagnosis? Osteosarcoma — an aggressive bone cancer — in the fibula, or lower leg bone, of a Centrosaurus apertus, a plant-eating, single-horned dinosaur that lived 76 to 77 million years ago.
The discovery opens up new understanding about other diseases that may have developed in dinosaurs, among other aspects of dinosaur life.
"What this study shows, because we found bone cancer at quite an advanced stage, is that dinosaurs were not only afflicted by bone cancer but probably all sorts of other cancers that we see in invertebrates today," says David Evans, a paleontologist at the Royal Ontario Museum and one of the study's lead researchers.
Though the diagnosis is new, the bone was discovered in 1989. That's when a crew from the Royal Tyrrell Museum in Drumheller, Canada, discovered the fibula in a massive bone bed in Alberta, Canada.
The fibula was badly malformed, but scientists initially assessed it as a healing broken bone, and that the odd shape was a fracture callous.
The bone sat in the museum's collection until 2017, when a team led by Evans and Mark Crowther, a professor of pathology at McMaster University, began to search through the hundreds of injured or partially healed bones on a mission.
"We basically went on a hunt for dinosaur cancer," Evans says.
Evans, Crowther and Snezana Popovic, an osteopathologist at McMasters, combed through hundreds of bones before they found the unusually malformed fibula to investigate for signs of cancer.
They brought in specialists in an array of fields, including pathology, radiology, orthopedic surgery and paleopathology, to examine and diagnose the suspected tumor.
"The approach we took in this case was very similar to how we approach a patient that comes in with a new tumor, and we don't know what kind of tumor it is," says Seper Ekhtiari, an orthopedic surgery resident at McMaster University who worked on the team.
They were able to visualize the progression of cancer through the bone by performing high-resolution CT scans of the fibula and examining thin sections of the bone at the cellular level under a microscope.
The team confirmed the diagnosis of osteosarcoma by comparing the bone to the fibula of a healthy centrosaurus and that of a human with osteosarcoma.
While this is the first identified instance of osteosarcoma in a dinosaur, Ekhtiari says it makes sense that a cancer associated with rapid bone growth would have plagued the dinosaurs.
"One of the ways they got to such massive sizes is that they grew extremely rapidly from the time when they were born," Ekhtiari says. "So finding this in a dinosaur is not surprising." In fact, he says, bone cancer "is probably more common than we think, or more common than we have found so far."
Crowther, the pathologist, adds that their finding suggests that dinosaurs likely suffered from other diseases that affect the bones — like tuberculosis and osteomyelitis.
Even though it points to a potential cause of death for dinosaurs, the cancer discovery also has given insight into how they lived and survived.
Take the diseased centrosaurus. While it would have been severely hobbled by the advanced stage of cancer found in its fibula, it didn't die from the disease, nor was it picked off by a predator like a Tyrannosaurus rex. Its bones were found in a massive bone bed, which scientists believe is the partial remains of a large herd drowned by a flood.
"The cancer was able to progress to the stage that it did because of the safety in numbers of the herd that it lived in," says Evans, the paleontologist.
While the discovery opens up many new doors in paleontology and pathology, one of the biggest impacts of the study might be a shift in the way we perceive dinosaurs.
"We often think of dinosaurs as sort of mythical, powerful creatures, and I think this discovery really underscores that they can be afflicted by diseases that we see around us today, even horrible fatal cancers," Evans says. "I think in an odd way it brings them even more back to life."
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