A collection of Megalodon teeth on display at a museum. Image credit: mattgyver (CC0)
Teeth are among the most diverse and complex organs in the animal kingdom that have evolved over millions of years to accommodate a wide range of diets and habitats. Their shapes vary broadly between and within species, and even among individuals, which often possess multiple tooth types within a single dentition.
Mammals and sharks both exhibit particularly high tooth diversity, having diverged from a common ancestor several hundred million years ago. Comparing their dentitions, therefore, provides a valuable opportunity to investigate how these organs evolved, how they develop, and what they reveal about past ecosystems and animal behaviors.
Although mammalian and shark teeth form through distinct developmental mechanisms, both groups share key principles. For example, in both groups, large-scale features – such as tooth position within the mouth – are established before finer details, such as small cusps or serrations.
Zimm et al. sought to determine which levels of anatomical organization are most informative for understanding how composed functional traits like dentitions evolve and adapt. This question is critical because many biological functions arise from the integration of traits across multiple spatial scales – from fine serrations and cusps to differences between teeth and jaws – and establishing a methodological framework for comparing these levels has remained a major challenge. Moreover, while isolated shark teeth have been studied previously, little is known about how sharks have adapted to different ecological niches.
To address this, Zimm et al. developed a new methodology for comparing dentitions using an online collection of shark teeth combined with genomic data. Their analyses revealed strong statistical differences in types of dental complexity between the two major shark groups and the different environments they inhabit, especially the deep sea and the open ocean. For example, the way neighboring teeth differ from each other is more shaped by their ecological niches rather than by genetic relationships, while the latter explains more details within teeth or dental differences between jaws.
These findings provide new insights into how integrated biological systems adapt and evolve. Because shark dentitions are tightly linked to ecological function, this work may also offer new avenues for studying long-term changes in marine ecosystems. Together, these perspectives could play an important role in developing both general and specific predictions about how the biosphere may evolve in a rapidly changing world.
