255-Million-Year-Old Tumor Is Oldest of its Kind

The animal was a distant relative of modern mammals that lived before dinosaurs walked the Earth, and the new discovery shows that these tumors existed long before mammals evolved, according to the researchers who found the tumor. The benign tumor, known as a compound odontoma, is made up of tiny, tooth-like structures, said the researchers, who found it in the gorgonopsian's fossilized jaw.