Tumor Discovered In A 225-Million-Year-Old Fossil

The 225 million year old tumor

The tumor is located at the base of another fully developed tooth. Christian Sidor/Megan Whitney

Researchers found evidence of a tumor nestled in the jaw of a creature that lived over 200 million years ago. The fossil in which it was found originally belonged to a gorgonopsian, or “gorgon-faced” animal, that would have been one of the dominant predators of its day.

The scientists first noticed the apparent tumor when examining the teeth of the fossil. They realized that at the base of one tooth there was a little cluster of other tooth-like structures, with clearly defined layers of dentin and enamel. Identifying it as a type of benign tumor known as a compound odontoma, they are commonly found in mammals alive today. Except this specimen walked the Earth 225 million years ago, before mammals had even evolved.


This makes it the oldest ever example of an odontoma, and potentially the first ever identified in an animal that is not a mammal. Gorgonopsians tend to be referred to as “mammal-like reptiles”, as despite showing some mammalian features, they came before mammals truly evolved. The creatures were active predators during the Permian period, and were one of the most fearsome animals during the Middle Permian.

Gorgonopsians were a diverse group, such as this Arctops watsoni from South Africa. Nobu Tamura/Wikimedia Commons

One of the defining differences between reptiles and mammals is how their teeth develop, and it was this aspect of the gorgonopsian fossil that the researchers were initially investigating. “Most reptiles alive today fuse their teeth directly to the jawbone,” explains Megan Whitney, who co-authored the study published in JAMA Oncology, in a statement. “But mammals do not: We use tough, but flexible, string-like tissues to hold teeth in their sockets. And I wanted to know if the same was true for gorgonopsians.”

To do this, she had to take a gorgonopsian fossil and slice it into sections to see how the teeth are set into the jaw bone. It was whilst doing this that Whitney discovered the toothlets. “At first we didn't know what to make of it,” says Whitney. “But after some investigation we realized this gorgonopsian had what looks like a textbook compound odontoma.”


The amazing discovery gives an insight into the illnesses that animals over 200 million years ago were facing, while also showing us the deep origins of some of our own diseases.

Detail of the odontoma, showing the distinct layers in the toothlets. Christian Sidor/Megan Whitney


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