Study overturns theory on bonnethead shark head shape development

September 5, 2026 at 03:33 AM2 min

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A University of Miami study found bonnethead shark heads become more rounded with age, especially in females, overturning the theory that males develop pointed snouts at sexual maturity. The research tracked 144 sharks across Biscayne Bay and Tampa Bay from May 2022 to May 2023. Diet and foraging differences did not explain the sex-based head shape variation.

Key Facts

The study sampled 105 bonnethead sharks in Biscayne Bay and 39 in the Tampa Bay region between May 2022 and May 2023.
Lead author Kathy Liu conducted the research while earning her master's degree at the University of Miami Rosenstiel School.
Co-author Catherine Macdonald directs the Shark Research and Conservation Program at the Rosenstiel School.
Bonnetheads are the only shark species known to show clear sex-based differences in head shape.

Head Shape Development

Researchers from the University of Miami Rosenstiel School and collaborating institutions found that bonnethead sharks' shovel-shaped heads become more rounded as both males and females grow older, with the change especially pronounced in females. Earlier research had suggested that males developed their more pointed snouts when they reached sexual maturity. Kathy Liu, lead author of the study, stated that younger males and females both had more pointed heads, but the head became rounder as the sharks matured, with the change much greater in females. The research is the first detailed investigation of both head shape and diet in bonnethead sharks from Biscayne Bay, and included sharks from Tampa Bay to compare developmental patterns across Florida.

Diet and Foraging

The researchers tested whether males and females might develop different head shapes because they eat different foods or forage in different ways. Results showed that bonnetheads in Biscayne Bay and Tampa Bay occupied distinct food webs and experienced dietary changes as they grew. However, males and females living within the same bay depended on many of the same local food sources. Liu said the findings provided no evidence that differences in diet or foraging were driving the development of the sharks' sex-specific head shapes.

Implications

Catherine Macdonald, a co-author of the study and associate professor in the Department of Environmental Science and Policy, said the study helps narrow the drivers of a biological trait that has puzzled scientists. By examining body shape and diet in the same animals, the team was able to assess whether diet and morphological changes co-occur. Macdonald stated that the results suggest there is another cause behind the differences in head shape between male and female bonnetheads.