How Fish Evolution Is Limited by a Trade-Off Between Tooth Size and Jaw Mobility

A trade-off between tooth size and jaw mobility has restricted fish evolution, according to a study by Nick Peoples and colleagues at the University of California Davis, US. Ray-finned fish, representing 99% of living fish species, have evolved two key adaptations: large teeth and extendable jaws.

Researchers found that fish with larger teeth can access a wider range of food sources, while those with the ability to rapidly extend their upper jaw can hunt fast-swimming prey using suction forces. However, these two traits are rarely seen together in the same fish species.

By analyzing the feeding behavior of 161 ray-finned fish species through high-speed videos, the study revealed that small-toothed fish use various methods to capture prey, including jaw extension for suction. On the other hand, fish with larger teeth tend to rely on rapid bursts of swimming to catch their prey, with the largest teeth exclusively using this strategy.

The research suggests that large teeth and a highly extendable upper jaw are incompatible adaptations, leading to a trade-off in fish feeding behavior evolution. Most ray-finned fish grow replacement teeth inside the jawbone, which may limit tooth size. The study proposes that slender, mobile jaws are better suited for rapid extension, explaining why fish using jaw extension for prey capture have relatively small teeth.

Peoples highlighted that species with exceptionally large teeth often have unique dental system modifications, such as the beak of parrotfish. The study emphasizes the importance of considering the interactions between different feeding traits in fish evolution.

Peoples also noted the value of high-speed videography in understanding fish feeding behavior, revealing subtle movements and behaviors that may go unnoticed. Despite the challenges of observing natural feeding behaviors in the lab, working with live fish remains a rewarding experience for researchers.

For more information, refer to the study titled 'Incompatibility between two major innovations shaped the diversification of fish feeding mechanisms' published in PLOS Biology (2025).