Tooth decay is not only common among humans. Researchers have now shown that the small primate species Microsyops latidens suffered from this bacterial dental disease as early as 54 million years ago. The fossil teeth of this animal discovered in the USA show the typical caries tooth holes. The reason for this was probably a high-sugar diet with sweet fruits and vegetable juices. The analyzes also provide information on how the diet of these primates has changed over the millennia.
When paleontologists want to study the diet of extinct animal species, they often analyze how the jaws and teeth of the fossils are shaped. However, changes in diet can only be found on very large time scales, because it takes many generations for the shape of the teeth to adapt to a new diet. On the other hand, more short-term information can be provided by the wear and tear on the teeth, for example tiny scratches indicating what the animal last ate.
Largest and oldest collection
The anthropologists Keegan Selig and Mary Silcox from the University of Toronto Scarborough in Canada have now chosen a third method: They analyzed prehistoric teeth for traces of tooth decay. “Tooth decay sheds light on important aspects of an individual’s life, such as diet and health, so past patterns of tooth decay rates may shed light on the ecology of extinct animals,” they write. “Since an increased sugar content in food causes tooth decay almost immediately, dental caries can also serve as a guide for changes in diet – faster than the shape of the teeth and somewhat more long-term than a wear analysis. In this way, the analysis of dental caries fills a gap in the timescale that can be investigated. “
For their study, Selig and Silcox analyzed the teeth of 1,030 individuals of the early primate species Microsyops latidens, which lived in North America during the Eocene around 54 million years ago. The teeth were collected during a nearly 50 year long field project in the southern Bighorn Basin, Wyoming, USA, and represent the largest and earliest collection to date to have been examined for tooth decay. The teeth came from different sedimentary layers and represent a period of over 500,000 years in the early Eocene.
More tooth decay than contemporaries
Because the teeth were completely dark in color due to their age, the researchers were unable to identify tooth decay using dark spots, as is common with younger specimens. Instead, they paid attention to typically shaped holes in the teeth, which they made visible with the help of micro-computed tomography. The result: “In our sample of 1030 individuals, we found tooth decay in 77 of these individuals, that is 7.48 percent of the sample,” the researchers report.
Compared to other extinct primates, this caries percentage is very high. “Our results most closely match the frequencies observed in tamarins living in the wild today, which are known to consume a lot of sugary foods such as fruits and vegetable juices,” said Selig and Silcox. They therefore adopt a similar form of nutrition for M. latidens. When the researchers compared teeth from different sediment layers, i.e. from different times, they noticed noticeable changes over time: the oldest and youngest teeth were less affected by tooth decay than the rest of the sample. In one of the middle sediment layers, five out of 29 individuals were affected by tooth decay, i.e. 17.24 percent.
Climate fluctuations as a possible cause
In an earlier study in which Selig and Silcox examined the shape of the teeth of M. latidens, they concluded that the diet of the small primates probably changed little over time. Only for a short period in between did the shape of the teeth suggest that the primates were increasingly eating fruits during this period. The current study confirms this by showing that the caries rate increased shortly before. The time lag can be explained by the fact that the changed diet immediately caused more tooth decay, but only led to an adapted shape of the teeth after generations. The researchers were thus able to confirm that analyzes of the frequency of caries can complement and refine other methods.
According to the researchers, a cause for the changed diet of M. latidens could have been a local climate change. “Microsyops latidens may have resorted to more sugary and therefore more caries-causing food sources in times of climate change because the competition for limited food sources increased or the available food sources changed,” they write. Further evidence from the same period could help to support this thesis.
Source: Keegan Selig and Mary Silcox (University of Toronto Scarborough, Canada), Scientific Reports, doi: 10.1038 / s41598-021-95330-x