Cancer in the tree of life is an archaic natural phenomenon, found in dinosaur fossils, Egyptian mummies, and now the oldest known stem-turtle from the Triassic period. The study of such deadly diseases in antiquity has important implications for the way we understand the evolution of pathogens and the environment around us.
“Generally, paleopathologies are rare in fossils, particularly malignant cancers which are almost unheard of in the fossil record, making this a rare find indeed,” said co-author Patrick Asbach, radiologist at the Charité Hospital Universitätsmedizin Berlin, in a statement.
Through the years, we’ve found some animals have a high propensity for cancer while others seem less susceptible to its ruinous abilities. Unfortunately, it seems the stem-turtle – the name for extinct relatives of modern turtles – may have been on the wrong side of biology. Paleontologists and physicians from three countries used morphological inspection and micro-CT scans to diagnose the 240-million-year-old stem-turtle (Pappochelys rosinae) with bone cancer.
The turtle, which physically appears more similar to an iguana, was first collected in 2013 in a region that was once an ancient lake in southwestern Germany. Upon its discovery, it was described as a possible “missing link” in turtle evolution, a species that had yet to grow a shell like the ones we see on turtles nowadays.
For the current research, published in JAMA Oncology, the team inspected the creature’s femur, which first piqued their curiosity when they spotted a mysterious growth on it. Further investigation diagnosed it as periosteal osteosarcoma, a malignant form of bone cancer.
The study suggests uncontrolled cell growth “occurred as early as the Triassic period and that cancer is not a modern physiological defect but rather a vulnerability that is rooted deep in vertebrate evolutionary history.”
Whether this species experienced other types of cancer is unknown, primarily because soft tissue doesn’t preserve well in the fossil record, which means paleontologists are limited to the hard remains that linger millions of years later.
Dedicating time to fossil pathologies helps scientists determine when certain traits appeared in history. In this case, a cell growth gene “has likely been mutated causing a malfunction, in humans these are called tumor suppressor genes and they are a hot topic of medical research,” said co-author Nadia Fröbisch from the Museum für Naturkunde Berlin.
However, the team can't say whether this Triassic turtle had the same kind of cancer-causing genes as humans or whether it died of its disease.
“Our finding provides further evidence that cancer is not restricted to the modern human physiology. Instead, the susceptibility to this disease roots far back in the evolutionary history of vertebrates, hundreds of millions of years before the origin of humans,” said lead author Yara Haridy.