UW News

December 8, 2016

Frequently asked questions: odontoma in a gorgonopsian

A fossilized skull.

A gorgonopsid skull, but not the one in which the odontoma was found.Christian Sidor/University of Washington

Prepared by Christian Sidor and Megan Whitney with the University of Washington and the Burke Museum of Natural History & Culture. University of Washington press release here.

Major findings

Our discovery of odontoma in a gorgonopsian fossil demonstrates that this type of tumor has existed for at least 255 million years and predates mammals.

Frequently Asked Questions

Sketch of an extinct animal.

Sketch of a gorgonopsian head, in side view.CCA 3.0/Dmitry Dogdanov

What are gorgonopsians?

  • Gorgonopsians were a group of carnivorous, land-based vertebrates that lived between about 270 to 252 million years ago during the middle and late Permian Period. Their fossils are known from Africa and Russia.
  • Gorgonopsians are distantly related to living mammals, but they lie “on the mammalian line,” meaning that they are more closely related to humans than to dinosaurs or other reptiles.
  • Gorgonopsians ranged in body size from 2 to 10 feet long, from the length of a bobcat to that of a polar bear.
  • Gorgonopsians are sometimes known as the “saber-tooths of the Permian,” for their enlarged canine teeth.

What is an odontoma?

  • The World Health Organization defines a compound odontoma as: “A malformation in which all the dental tissues are represented in a more orderly pattern than in the complex odontoma, so that the lesion consists of many tooth-like structures. Most of these structures do not morphologically resemble the teeth of the normal dentition, but in each one enamel, dentine, cementum and pulp are arranged as in the normal tooth.”
  • Odontomas are one of the most common odontogenic tumors, constituting approximately 20 percent of odontogenic tumors. Ameloblastoma is the most common with 39.6 percent of odontogenic tumors.
  • Odontomas are not cancer. They are considered benign tumors, though in humans they are often surgically removed.
A fossilized jawbone.

A photograph of a partial gorgonopsid lower jaw, but not the specimen in which the odontoma was discovered.Christian Sidor/University of Washington

Where was this specimen found?

  • The gorgonopsian jaw with the odontoma was found in southern Tanzania in the Ruhuhu Valley in 2007.
  • The specimen is about 255 million years old, based on dating of similar fossils in South Africa.

How did we find this pathology?

  • There were no external indications of a pathology. We were thin-sectioning this specimen for an entirely different project —examining the tissues involved in tooth attachment.
  • UW undergraduate researcher Larry Mose noticed a pathology along the root of the canine only after the specimen had been cut.
An image of a tooth.

A histological thin section of the gorgonopsid lower jaw, taken near the top of the canine root. The dark area on the right is bone. The backward C-shaped structure on the left is the canine root. The cluster of small circles resemble miniature teeth, indicative of compound odontoma.Megan Whitney/Christian Sidor/University of Washington

What is thin-sectioning?

  • We make thin-sections of fossil bones and teeth so that we can study the fine, inner details of their hard tissues. These small details act as storybooks, preserving a lot of information about the biology of these animals while they were alive. As is easy to imagine, studying the biology of animals that lived millions of years ago can be challenging. We use the microstructure of fossil hard tissues to reveal aspects of their biology like growth rate, age and disease that otherwise would be inaccessible for us to study in these ancient animals.

Has an odontoma been found in the fossil record before?

  • This is not the first time an odontoma has been reported in the fossil record. Previous instances include:
    • A Woolly mammoth from the Netherlands from the last glacial age, known as the Weichsel Glacial in Northern Europe, ca. 115,000-10,000 B.C.
    • Fossil red deer from France from 12,200-11,400 B.C.
    • Several recorded instances in archaeological material.
  • All reported instances, however, are relatively recent in the history of life on earth —to within the last 1 million years or so.

Is this the oldest occurrence of tumors in the fossil record?

  • There is a decisive case of cancer reported in a lower Carboniferous fish (300 million years ago), and a possible case of cancer in fossil fish from the Devonian (350 million years ago).
  • But this is the oldest reported case of an odontoma. See above question.

How do teeth form?

  • Teeth are derived from two major tissue layers, the outer epithelial layer that gives rise to enamel and an ectomesenchyme layer that gives rise to dentine and pulp.
  • Odontomas arise when there are developmental anomalies involving both the epithelial and ectomesenchymal tissues. These anomalies give rise to tooth-like structures that have enamel, cementum, dentine and pulp in their normal anatomical relationships.
An image of a tumor made of teeth.

Each odontoma resembles a miniature tooth, with enamel on the periphery, dentine forming the bulk of the tooth and a pulp cavity at its center.Megan Whitney/Christian Sidor/University of Washington

What did we learn? What are the implications?

  • This is the oldest occurrence of odontoma in a mammal relative. Odontoma has remained relatively unchanged for 255 million years.
  • Paleontology can contribute to medicine by shedding light on the history of disease.


  • Laurent Nampunju and Anthony Tibaijuka (Antiquities Division, Ministry of Natural Resources and Tourism) for assistance with fieldwork in Tanzania.
  • Field team for helping to collect the fossil (Ken Angielczyk, Sterling Nesbitt, Roger Smith, Linda Tsuji).
  • Oral Biology group at the University of Washington for helpful discussions.
  • Royal Ontario Museum histology lab for use of thin section and imaging equipment.

Grant support

  • National Geographic Society (NGS 7787-05) to C. Sidor (for fieldwork to collect fossils)
  • National Science Foundation (DBI 0306158) to Ken Angielczyk, Field Museum of Natural History, Chicago (for fieldwork to collect fossils)
  • National Science Foundation (EAR 1337569) to C. Sidor (for research and analysis)

For additional information, contact Christian Sidor at casidor@uw.edu and Megan Whitney at megwhit@uw.edu. University of Washington press release here.