Odontoma in a 255-Million-Year-Old Mammalian Forebear

Abstract

This study describes cancer in a 255-million-year-old mammalian forebear and comments on the implications for establishing the phylogenetic and physiologic conditions under which such pathologic conditions first arose.

Figure 1.. Family Tree Showing the Relationship of Gorgonopsians and Mammals to Other Synapsids

The mammalian and reptilian lines diverged approximately 320 million years ago, with the group that included extant mammals appearing approximately 165 million years ago. Gorgonopsians (in blue) lacked many canonical mammalian features, such as large brain size, diphyodonty, distinct thoracic and lumbar vertebrae, and 3 middle ear ossicles, which evolved later along the lineage marked 1. Odontomas have been recognized in the groups indicated by stars (gorgonopsians, humans, horses, mammoths, and deer).

Figure 2.. Histologic Evidence for Odontoma in a 255-Million-Year-Old Gorgonopsian

A, Computed tomogram of a gorgonopsian anterior dentary (red) with dentition (blue) highlighted (National Museum of Tanzania specimen RB382), indicating approximate positions of thin sections where the pathologic features are visible (National Museum of Tanzania specimen RB404). Successive slides representing the cervical (B) and midroot (C) portions of the functional root with odontomes. D, Clustering of odontomes at the apical end of the tooth root. All histologic images were taken under cross-polarized light. ca indicates root of canine; d, dentine; e, enamel; i, root of incisor; od, odontome; and pc, root of postcanine.