About 240 million years ago in what is now Germany, a turtle that hadn’t yet evolved a shell developed something much less fortuitous: a kind of bone tumor that afflicted one of its hind legs.
The fossilized tumor, described today in the journal JAMA Oncology, shows that even in the Triassic period, at around the time the first dinosaurs appeared, animals could be plagued with mutations in their DNA that led to cancer.
The find is exciting, because “cancer is ridiculously rare in the fossil record,” says study leader Yara Haridy, a paleontologist at Berlin’s Museum of Natural History. “Most cancers are in soft tissues, and although we can see sometimes evidence of soft tissue pathologies on [fossil] bone, cancer would be really hard to diagnose that way.” (Today, for example, a virus is causing sea turtles to suffer from life-threatening tissue tumors.)
The study team determined that the ancient growth was a kind of bone cancer called a periosteal osteosarcoma—one that “looks almost exactly like osteosarcoma in humans,” says coauthor Patrick Asbach, a medical doctor and radiologist at Berlin’s Charité University of Medicine. This specific type of bone cancer afflicts about 800 to 900 of the 3,450 or so people who are diagnosed with skeletal cancers each year in the U.S. today.
“It is interesting to see that the diseases we know quite well also appeared in extinct animals, and that we as humans are not the only ones who struggle with it,” Asbach says.
Missing link in turtle evolution
The shell-less turtle relative sporting the tumor, Pappochelys rosinae, was first revealed to the world in 2015. At the time, the Chihuahua-size species was hailed as the final piece in the puzzle showing how turtle shells evolved from flattened ribs and belly bones into the armored body boxes they are today.
Around 20 specimens of Pappochelys were discovered in 2008 at a limestone quarry near the town of Velberg, about 50 miles northeast of Stuttgart, Germany. The fossils have since been held at the State Museum of Natural History Stuttgart.
Among them was a thighbone with a puzzling growth that came to Haridy’s attention last summer. She then recruited Asbach to help conduct a micro-CT scan to look inside the fossil bone and see its internal structure, which allowed the team to determine the type of cancer involved.
While it’s impossible to know for sure if the cancer this turtle suffered from led to its demise, in human cases of osteosarcoma, it often spreads to the lungs.
“If it did spread to the lungs, it may have made the turtle less efficient in escaping or feeding, which could have ultimately caused its death,” Haridy speculates.
While it is relatively common to see pathologies in fossil bones, the majority are the result of traumatic injuries such as bites and breaks, says Steve Salisbury, a paleontologist at the University of Queensland in Australia who has researched infectious disease in T. rex fossils.
“Only rarely are we able to link pathologies in fossil vertebrates to known diseases,” adds Salisbury, who was not one of the study authors. “It would be interesting to compare the fossil bone with examples of similar cancers in modern turtles, assuming the ones that afflicted them in the Triassic still do today.” (Also see a fossil toe that holds the earliest known case of cancer in humans.)
Cancer’s very ancient origins
Scientists have found several other very ancient cancers in fossil fish and an amphibian, and a non-cancerous tumour in a slightly older mammal relative called a gorgonopsid. However, this new find is the earliest cancer ever discovered in an amniote, the group that includes reptiles, birds, and mammals.
A young woman exhales cigarette smoke in Shanghai, China. The People's Republic of China is both the world's largest producer and largest consumer of tobacco, which has led to an impending cancer epidemic in the most populous country on Earth.
The discovery of an osteosarcoma helps dispel a belief held by some experts that diseases change so much over time that “current disease manifestations cannot be used to recognize past afflictions,” says coauthor Bruce Rothschild, a professor of medicine at the University of Kansas and a research associate at the Carnegie Museum who has studied cancer in dinosaurs.
“Not only could cancer be recognized and the diagnosis confirmed, but it could even be diagnosed down to a specific variety.”
And while it is true that modern cancer-causing agents such as nicotine and alcohol can increase our chances of developing cancer, the discovery of a tumor from the Triassic adds to evidence that many of the cancers we have today and their associated genes are likely to have very ancient origins, the experts argue.
“We are not very different,” Rothschild says, “from all those with whom we share and have shared this planet.”