Scientists discover bonnethead sharks' heads change shape with age

Scientists have overturned a long‑held idea about the head shape of bonnethead sharks. In a new study, researchers from the University of Florida and the Smithsonian Institution showed that both male and female bonnetheads start with pointed heads. As they age, the heads round out, especially in females. The paper appeared in the journal *Marine Biology* last week.

Bonnethead sharks are small, reef‑dwelling sharks found in the Gulf of Mexico and Atlantic. Their head shape has been used to identify males and females and to understand how they hunt and mate. Earlier work suggested that males develop a sharp snout when they reach adulthood, giving them an advantage in fights for mates. That view was based on limited samples and a few observations.

The new research examined 150 sharks of different ages, from juveniles to adults. Researchers measured the length of the snout and the width of the head at the eye. They found that all sharks, regardless of sex, had a relatively long snout when they were young. After about 4–5 years, the snout shortened and the head became broader. Female sharks showed a steeper change. Dr. Jane Smith, a marine biologist not involved in the study, said the findings change how scientists think about sexual selection in this species. The