Image of not-to-scale renderings of the skulls of various primate species
Image of not-to-scale renderings of the skulls of various primate species

Surface Area of Tooth Roots Predicts Primate Body Size

Researchers determine that a primate’s tooth root, and not just its crown, can yield reliable information about body size, but the relationship between root surface area and diet isn’t as clear.

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Maddie Bender

Maddie Bender is a Boston-based science and health writer. She holds bachelor’s degrees in evolutionary biology and Classics, and a public health master’s degree in microbial disease epidemiology from Yale.

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May 2, 2022

ABOVE: Not-to-scale renderings of the skulls of various primate species, including the crowned lemur (Eulemur coronatus, center), with the analyzed teeth shown in blue Ashley Deutsch and Adam Hartstone-Rose

EDITOR’S CHOICE IN PHYSIOLOGY

Animals’ remains are often incomplete, but even a handful of teeth can reveal key traits, including an organism’s size and diet. Typically, a tooth’s crown (the portion above the gum) is used to extrapolate these details, but North Carolina State University biologist Adam Hartstone-Rose and colleagues recently explored whether tooth roots, which are less likely to chip or crack than crowns, might provide useful information too.

Hartstone-Rose’s group mapped the tooth root surface area (TRSA) of 75 rear teeth—those behind the canines—from the lower jaws of 73 extant primate species and compared their measurements to estimates of body size for each individual. The team also categorized each specimen by its diet—whether it ate insects, fruits, leaves, or hard foods such as bones or seeds—and plotted the variation in TRSA for each category. The team found a strong, positive correlation between root surface area and body size, but the relationship between TRSA and diet varied across lineages.

The researchers plan to look at other types of teeth, including those in the upper jaw, to determine whether they have a closer relationship to diet, says biologist Ashley Deutsch, a PhD student in Hartstone-Rose’s lab who completed the work for her dissertation. Meanwhile, the team has added TRSA to its toolkit for analyzing tricky specimens. “Just knowing how big [an animal] is tells you enormous amounts about how it interacts with the environment,” says Hartstone-Rose. 

Peter Ungar, an anthropologist at the University of Arkansas who was not involved in the research, calls the study an example of “good science,” but adds that establishing a clearer link to diet would be even more useful, especially if the metric was used to study extinct species about which far less is known. “There would have been a much bigger splash if you found an entirely new way of reconstructing diet in the past.”

A.R. Deutsch et al., “Primate body mass and dietary correlates of tooth root surface area,” Am J Biol Anthropol, 177:4–26, 2022.

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