Email Print Share

News Release 16-150

Scientists discover fossil tumor in 255 million-year-old mammal forerunner

Ancient tumor was hidden inside fossil from Tanzania

A thin-section image zooms in on the fossil odontomas. Each looks like a miniature tooth.

A thin-section image zooms in on the fossil odontomas. Each looks like a miniature tooth.

December 8, 2016

This material is available primarily for archival purposes. Telephone numbers or other contact information may be out of date; please see current contact information at media contacts.

When paleontologists cut into the fossilized jaw of an ancient creature, they got more than they bargained for: a toothy tumor.

As the scientists report in a paper published today in the Journal of the American Medical Association Oncology, they discovered evidence that the specimen harbored a benign tumor made up of miniature, tooth-like structures. This type of tumor, known as a "compound odontoma," is common to mammals today. But this animal lived 255 million years ago -- before mammals existed.

"We think this is by far the oldest known instance of a compound odontoma," said paper author Christian Sidor, a vertebrate paleontologist at the University of Washington. "It would indicate that this is an ancient type of tumor."

Before this discovery, the earliest evidence of odontomas came from ice age-era fossils.

"Until now, the oldest known occurrence of this tumor was about 1 million years ago in fossil mammals," said Judy Skog, program director in the National Science Foundation (NSF) Division of Earth Sciences, which funded the research. "These researchers have found an example in the ancestors of mammals that lived 255 million years ago. The discovery suggests that the suspected cause of an odontoma isn't tied solely to traits in modern species, as had been thought."

Skog added that the research demonstrates that paleontology can contribute to medical research. "This finding shows that the fossil record can play an important role in understanding how diseases evolve."

Mass of small "toothlets"

In humans and other mammals, a compound odontoma is a mass of small "toothlets" combined with tooth tissues like dentin and enamel. This type of tumor grows in the gums or other soft tissues of the jaw. It can cause pain and swelling and disrupt the positions of teeth.

Doctors consider odontomas benign tumors because they do not metastasize and spread throughout the body. But given the disruptions they cause, surgeons often opt to remove them.

The creature studied by the team didn't have the option of surgery. It was a gorgonopsian, a distant relative of mammals and the apex predator during its pre-dinosaur era, about 255 million years ago. Gorgonopsians are part of a larger group of animals called synapsids, which includes modern mammals as its only living member.

Some synapsids are called "mammal-like reptiles" because they possess some, but not all, the features of mammals. The first mammals evolved more than 100 million years ago.

"Most synapsids are extinct, and we -- that is, mammals -- are their only living descendants," said paper author Megan Whitney of the University of Washington. "To understand when and how our mammalian features evolved, we have to study fossils of synapsids like the gorgonopsians."

Slicing into a fossil

Paleontologists have categorized many "mammal-like" features of gorgonopsians. For example, like us, they have teeth differentiated for specialized purposes. But the researchers started studying gorgonopsian teeth to see if they had a different mammalian feature.

"Most reptiles alive today fuse their teeth directly to the jawbone," said Whitney. "But mammals do not. We use tough, but flexible, string-like tissues to hold teeth in their sockets. We wanted to know if the same was true for gorgonopsians."

A purely external examination of gorgonopsian fossils wouldn't answer that question. The scientists had to take the risky approach of slicing into a fossilized gorgonopsian jaw. By looking at thin sections of jaw and tooth under a microscope, they could see how a tooth was nestled within its socket.

Since this technique would damage the fossil, Whitney and Larry Mose, also of the University of Washington, used an "orphan" gorgonopsian lower jaw -- one that wasn't matched to a more complete fossil -- that Sidor had collected in southern Tanzania.

Mose prepared multiple thin slices from the gorgonopsian jaw, each only about as thick as a sheet of notebook paper, and mounted them onto slides. He and Whitney immediately noticed something unexpected within the jaw. Embedded next to the root of the canine were irregular clusters of up to eight tiny, round objects.

At higher magnification under a microscope, Whitney discovered that the objects in each cluster resembled small, poorly differentiated teeth, or toothlets. The toothlets harbored distinct layers of dentin and enamel.

"At first we didn't know what to make of it," said Whitney. "But after some investigation we realized that this gorgonopsian had what looked like a textbook compound odontoma."

Oldest odontoma

This is by far the oldest reported evidence for an odontoma, the scientists say, and possibly the first case in a non-mammal.

According to Sidor, odontomas have been reported in archaeological specimens, as well as in fossilized mammoths and deer. But those cases all date to within the last million years or so.

Since this synapsid had an odontoma, it would indicate that this condition existed well before the first mammals evolved.

"This discovery demonstrates that the fossil record can tell us a lot about our present-day lives, even the diseases or pathologies that are part of our mammalian heritage," Sidor said. "From the outside, you could never tell that this creature had this."

A University of Washington Mary Gates Research Fellowship also funded the study.


Media Contacts
Cheryl Dybas, NSF, (703) 292-7734, email:
James Urton, University of Washington, (206) 543-2580, email:

The U.S. National Science Foundation propels the nation forward by advancing fundamental research in all fields of science and engineering. NSF supports research and people by providing facilities, instruments and funding to support their ingenuity and sustain the U.S. as a global leader in research and innovation. With a fiscal year 2023 budget of $9.5 billion, NSF funds reach all 50 states through grants to nearly 2,000 colleges, universities and institutions. Each year, NSF receives more than 40,000 competitive proposals and makes about 11,000 new awards. Those awards include support for cooperative research with industry, Arctic and Antarctic research and operations, and U.S. participation in international scientific efforts.

mail icon Get News Updates by Email 

Connect with us online
NSF website:
NSF News:
For News Media:
Awards database:

Follow us on social