Multi-cusped postcanine teeth are associated with zooplankton feeding in phocid seals.

The morphology of an animal's teeth often reflects its diet. A well-known example of a mammal that feeds in the water is the crabeater seal (Lobodon carcinophaga), which consumes large amounts of zooplankton. Crabeater seals have complex, jagged teeth, which are believed to function as a sieve to retain krill in their mouths and filter it from seawater. Furthermore, recent studies have shown that the Baikal seal (Pusa sibirica) also preys on large quantities of zooplankton and possesses distinctive jagged teeth. Thus, while behavioral observations and tooth morphology studies suggest a connection between tooth structure and zooplankton predation, no studies have quantitatively demonstrated this link or revealed a consistent pattern across seal species.

In this study, we quantified tooth morphology, including jaggedness, using skeletal specimens (Fig. 1) of 13 species of seals from the collection of the National Museum of Nature and Science, focusing mainly on Baikal seals and their relatives. We examined the relationship between tooth morphology and zooplankton prey consumption. Baikal seals, known to consume large amounts of zooplankton, exhibited a unique tooth morphology compared to closely related species (see Fig. 2). Furthermore, our findings suggest that the degree of jaggedness in teeth correlates with the amount of zooplankton preyed upon, a trend observed across the entire seal family (see Fig. 3). These results indicate that the functional role of jagged teeth as a sieve is not exclusive to crabeater seals but is common among many seals that feed on zooplankton.

In the future, we aim to investigate how this tooth morphology influences mouth movements and overall body movements, and whether predation efficiency differs between fish-eating and zooplankton-eating seals with jagged teeth.

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