Tumor in a 255-million-year-old mammal forerunner

The study of the evolution of life is not just a mere attempt to put the species on the evolutionary tree or to understand how populations develop particular traits. It’s far more than that. Let’s consider diseases, for instance. The research concerning the origin of diseases is among the most intriguing branches of the evolutionary studies as it helps to understand where they come from and what causes them.

Most of such studies are conducted on the species living today as it’s possible to test their reactions to particular changes in their organisms. And naturally, it’s also because we need to handle the diseases here and now.

Nevertheless, if we want to study the history of certain diseases, we should look at the paleontological data.

A new study by a team led by Megan R. Whitney from the University of Washington describes the oldest known occurrence of odontoma in the fossil record. Odontoma is a non-cancerous tumor associated with tooth development. The tumor is composed of dental tissues (enamel, dentin, and cementum) that grow irregularly. There are two main types of odontoma – the compound and complex odontoma, differing in the development of the tumor. When the first – compound – type occurs, the tumor is composed of visibly differentiated dental tissues. In the second type (the complex odontoma), the tissue is not differentiated.

The new study was based on the right lower jaw of a gorgonopsian. Gorgonopsia was a large clade of early synapsids that existed during the Permian. The best known representatives of the group include, for example, Gorgonops, Inostrancevia, and Rubidgea. Although being extremely popular and among the most iconic of all Permian vertebrates, the knowledge of the evolution of the group is rather poor. Still, they can be a great source of fascinating information.

Whitney and her team prepared histological sections of the jaw bone and identified a structure resembling the composed odontoma. A few fossil mammals having the odontoma have been described to date but all of them were just up to a few million years old. The new find, however, is approximately 255 million years old, thus suggesting that the members of the mammal branch of amniotes suffered from the disease long before the origin of the first mammals.

As the authors state, it’s clear that “the fossil record has the potential to provide an evolutionary context for modern pathologic features”.

Featured image © Jonathan Blair, National Geographic.

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