Dental fossils belonging to a species of prehistoric primate, Microsyops latidens, which date to the Early Eocene (around 54 million years ago) display the earliest known evidence ​of dental caries in mammals, according to a study published in Scientific Reports. Of 1,030 individual dental fossils (teeth and jaw sections) discovered in the Southern Bighorn Basin (Wyoming, United States), 77 (7.48%) displayed dental caries, likely caused by a high fruit diet or other sugar-rich foods. Changes in the prevalence of caries over time indicate that the primates’ diet fluctuated between foods with higher and lower sugar content. 

Keegan Selig and Mary Silcox compared the position of fossils in strata of sediment from the Southern Bighorn Basin to determine their age. Fossils could be dated based on the geological age of sediment in which they were found. The authors found that the earliest and latest occurring specimens had fewer caries compared to the rest of their sample, which may indicate that the primates’ diet fluctuated between foods with higher and lower sugar content. Selig and Silcox argue that fluctuating climates during the Early Eocene may have impacted vegetation growth and food availability.

The authors also found that there was a higher prevalence of caries in the fossils of Microsyops latidens compared to the frequencies reported in studies of primates alive today. Only the genera Cebus (such as capuchins) and Saguinus (such as tamarins) had a higher prevalence of caries than Microsyops latidens.