New method sheds light on the diet of the earliest primates

Around 75 million years ago, the euprimates emerged. They were the first true primates and the ancestors of all living primates today.

Some researchers have argued that insects were a central part of the diet for these early euprimates. However, new research suggests that plant foods may already have played an important role when the first euprimates appeared.

That is the conclusion of an international team of researchers whose findings have been published in the journal Nature Communications (link: https://www.nature.com/articles/s41467-026-73688-8). The study was led by researchers from Duke University in the United States, while Associate Professor Shan Shan from SDU’s Centre for Quantum Mathematics contributed to the analytical work.

Plant food was important for early pimates

In the study, the researchers analysed 500 molars from both living and extinct species belonging to the group Euarchonta. This group includes primates, such as apes, monkeys and lemurs, but also tree shrews, colugos and a number of extinct species closely related to primates. These latter, the tree shrews, colugos and extinct primate relatives, were used as a comparison group.

The analysis relied on a suite of computational tools for comparing 3D shapes, developed over roughly a decade by mathematicians at Duke University, including Shan Shan, then at Duke. With them, the researchers were able to divide tooth crowns into corresponding regions, measure the curvature of each, and investigate how these specific regions changed over the course of primate evolution.

According to the researchers, the analyses indicate that plant foods played an important role in the earliest primates. More specifically, they found evidence of a progressive reshaping of the molars. In particular, the front part of the lower molars changed: a pointed dental structure known as the paraconid was reduced and later disappeared independently several times in different primate lineages.

Suitable for crushing and grinding food

At the same time, the upper molars developed broader surfaces that are better suited to crushing and grinding food. The researchers interpret these changes as signs that primates were moving away from a strong dietary specialisation on insects and towards greater use of plant-based foods such as fruits, seeds and, later, leaves.

For centuries, palaeontologists have studied teeth in an effort to understand what our ancestors preferred to eat.

Traditionally, such studies have involved a degree of subjective judgement, since individual researchers had to decide whether a particular dental feature should be classified, for example, as “reduced” or “absent”.

The computational tools used in the study, make it possible to analyse teeth in a more objective and interpretable way.

Shan Shan concludes:

“What makes this kind of study possible is a whole team's effort over the past ten years — anthropologists and palaeontologists who collected, scanned and cleaned the data, and mathematicians who developed methods for automatically aligning shapes, finding corresponding regions across hundreds of different teeth, and measuring curvature robustly. Together we turn a question like 'how has the shape of teeth evolved over millions of years?' into something we can quantify, measure and interpret.”