Dental cavities or caries is a common disease among modern humans, affecting almost every adult. New research shows that Microsyops latidens, a species of stem primate from the Early Eocene epoch, had a high prevalence of dental caries (7.48% of individuals), with notable variation through time, reaching 17.24% of individuals from a particular interval.
Archicebus achilles, a tree-dwelling primate from the Eocene of China. Image credit: Xijun Ni / Chinese Academy of Sciences.
Microsyops latidens lived in what is now the United States some 54 million years ago (Early Eocene epoch).
It is one of the best-known species in the family Microsyopidae and is represented by thousands of specimens.
Microsyops latidens likely weighed about 670 g on average based on body mass estimates derived from teeth size.
However, the ancient animal was likely arboreal, sharing similarities with arboreal primates and colugos.
In terms of its diet, Microsyops latidens was likely an omnivore, relying on a combination of fruits and possibly leaves.
“The etiology of caries has been studied in great depth in humans, and to some degree in non-human primates,” said Dr. Keegan Selig and Dr. Mary Silcox from the Department of Anthropology at the University of Toronto Scarborough.
“Studies have also examined caries in a handful of fossil mammals from the Mid-Miocene to the Late Pleistocene, including studies on fossil primates, bears, and artiodactyls.”
“However, these incidences are rare, with only small samples of individuals showing caries.”
“Very little is known about caries in older fossil mammals, or about how caries frequency may vary over time within a single species.”
In their new study, the authors examined 1,030 individual dental fossils (teeth and jaw sections) of Microsyops latidens.
The specimens were collected over the course of an almost fifty-year field project from the Willwood Formation of the Southern Bighorn Basin of Wyoming, an area that has produced the largest sample of stratigraphically controlled mammalian specimens in the world.
Of 1,030 Microsyops latidens fossils, 77 (7.48%) displayed dental caries.
“The sample represents the earliest known incidences of caries among fossil mammals and the largest known collection of carious individuals for any fossil vertebrate taxon,” the researchers said.
They also 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.
“Fluctuating climates during the Early Eocene may have impacted vegetation growth and food availability,” they noted.
They 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,” they said.
The findings were published in the journal Scientific Reports.
K.R. Selig & M.T. Silcox. 2021. The largest and earliest known sample of dental caries in an extinct mammal (Mammalia, Euarchonta, Microsyops latidens) and its ecological implications. Sci Rep 11, 15920; doi: 10.1038/s41598-021-95330-x