Some orangutans acquire enamel defects at regular intervals, but not according to seasonal cycles

Objectives: Developmental defects of tooth enamel are associated with systemic physiological stress and have been linked to seasonal environmental factors such as rainfall, temperature, and fruit availability. Here, we evaluate whether linear enamel hypoplasia and accentuated perikymata occur with any cyclicity on lower canines and then whether cycles differ between Bornean and Sumatran orangutans.

Materials and Methods: Epoxy casts of lower canines from Pongo abelii (n = 14) and P. pygmaeus (n = 33) were evaluated for perikymata and dental enamel defects. Individual developmental sequences (IDSs) were generated for each canine, tracking the position of each defect in the context of continuous perikymata (time). Autocorrelation, a form of time‐series statistical analysis was run for each canine to identify whether any cyclicity of defect expression was discernable.

Results: Autocorrelation revealed cycles of defect expression within canines, but no common cycle periodicities were identified between individuals of the same species or across species. P. pygmaeus averaged more linear enamel hypoplasia per year than P. abelli, but no other comparisons (number of defects, number of perikymata between defects, and autocorrelation analysis) revealed differences between the species.

Discussion: Although no common patterns of defect expression were identified within or between P. abelli and P. pygmaeus, the potential for autocorrelation analysis is promising for primatological and paleoanthropological studies of seasonal phenomena.