Scientists have discovered the tell-tale signs of a variety of dinosaur diseases – and discovered that they are strikingly similar to those that affect animals today.
A certain horned dinosaur was having a bad day on a rainy, stormy day 77 million years ago in what is now south-eastern Alberta, Canada.
The adult Centrosaurus apertus, a medium-sized plant-eating cousin of Tyrannosaurus, had advanced malignant bone cancer in its shin. The cancer may have spread to other parts of the body, and it is thought to be terminal.
But this Centrosaurus probably didn’t die from bone cancer because, before it could, it and the thousands of other Centrosaurus in its herd were wiped out by a catastrophic flood caused by a tropical storm. The bonebed preserved after this mass death event helped provide important evidence that these dinosaurs moved in massive herds millions of years later. However, the diagnosis of this dinosaur’s osteosarcoma – a rare, malignant bone cancer more commonly found in children and diagnosed in approximately 25,000 people worldwide each year – did not come until 2020. It was the first time a dinosaur had been diagnosed with a malignant cancer, and it took a multidisciplinary team of scientists to confirm the case.
For decades, palaeontologists and palaeopathologists – scientists who study ancient diseases and injuries using fossils – have suggested the presence of cancer in dinosaurs, despite the fact that the tumours were previously thought to be benign. However, the 2020 osteosarcoma study is part of a rapidly expanding field of research aimed at diagnosing dinosaur diseases with expertise and equipment similar to that used to diagnose ailments in humans and animals today. The only difference is that they only have fossils to guide them.
“The field began as a speculative venture...
However, it is now a scientific endeavour, and we can scientifically test hypotheses and develop criteria “says Bruce Rothschild, a vertebrate palaeontology research associate at the Carnegie Museum of Natural History in Pennsylvania. “It turns out that the diseases that afflicted dinosaurs resemble those that affect humans or other animals.”
These investigations are revealing previously unknown details about dinosaur life and death. Some argue that they could also provide medical experts with new insights into diseases that are still affecting us today.
A rare find
When David Evans, a palaeontologist at the University of Toronto and curator at the Royal Ontario Museum in Canada, met Mark Crowther, a human haematologist and chair of the faculty of medicine at McMaster University in Canada, the search for a definitive diagnosis for a dinosaur with bone cancer began. They realised they could use their combined knowledge to look for an osteosarcoma.
Finding a potential case, however, was not an easy task. Pathologies on fossil specimens are frequently noted, but they are not curated – that is, organised according to this characteristic – according to Evans. Instead, diseased bones are typically dispersed throughout collections.
Snezana Popovich and others sifted through hundreds of bones at the Royal Tyrrell Museum in Drumheller, Canada. A bone pathologist at McMaster University identified potential signs of bone cancer on the shin bone of Centrosaurus apertus. “I’ll remember Snezana picking this bone up and saying, ‘I think this is bone cancer,'” Evans says.
The bone had a lump on the end of it that was labelled as a fracture callus, but it had several tell-tale signs of bone cancer even at first glance: it was visibly malformed and had large, unnatural foramina (open holes) around the lump.
The team, which had grown to include eight medical experts, including modern cancer specialists, and four palaeontologists, used every available method to confirm a diagnosis in their 77-million-year-old patient. They compared the bone to a normal Centrosaurus shin bone and a human calf bone with osteosarcoma. However, they also used X-rays, high-quality computed tomography (CT) scans, 3D reconstruction tools, and histology (thin sectioning of the bone) to create biopsies, allowing them to study it at the cellular level.
“That enabled us to make a positive cancer diagnosis that is comparable to what the doctors on my team suggested [they would make] in a human patient,” Evans says. We actually started serial sectioning the bone… We were able to follow the cancerous tumor’s path through the bone from the knee to the ankle.”
According to Penélope Cruzado-Caballero, a palaeontologist at the Universidad de La Laguna in Tenerife, Spain, the study demonstrates the importance of approaching pathologies in this multidisciplinary manner, including histology, which is a relatively new analysis.
A wide search
It’s becoming more common in palaeopathology to use modern techniques to make a medical diagnosis in this manner, rather than simply visually comparing dinosaur ailments to other examples of diseases in a “card-matching game,” according to Cary Woodruff, curator of vertebrate palaeontology at the Phillip and Patricia Frost Museum of Science in Miami, Florida. “Just because they appear similar does not imply that they are.”
Cruzado-Caballero recently reported another possible osteosarcoma case. This time it was on the toe of Bonapartesaurus rionegrensis, a 70-million-year-old duck-billed herbivore discovered in Patagonia, Argentina. To diagnose a tumour, her team used imaging data, microscopic analysis, and descriptions of the visible shapes.
“Our research assists us in understanding when diseases emerge throughout the history of life on Earth,” she claims.
Osteosarcoma has been traced back to the Late Cretaceous period. Although they did not use as many different techniques as Evans’ team, palaeontologists Yara Haridy and Rothschild used micro-CT scans to diagnose it in a 240-million-year-old Triassic stem-turtle.
Scientists are also investigating dinosaur diseases in the context of other archosaurs, a group of reptilian animals that includes crocodiles and birds today. According to Jennifer Anné, lead palaeontologist at The Children’s Museum of Indianapolis, the approach helps palaeontologists understand how dinosaurs fit into the overall tree of life.
Anné frequently works with veterinary scientists to compare the conditions found in living birds and crocodilians to those found in dinosaurs. “It’s almost like being a palaeozoologist,” she says. “Like saying, ‘Alright, this is an animal, how do I study it as an animal?'”.
This was the approach that led Anné and two colleagues to the first ever diagnosis of septic arthritis in a dinosaur in 2016 – a condition that can occur when microbes get into a joint, often after an injury.