WORLD NEWS
Bonnethead shark heads round with age rather than males growing a point
Bonnethead sharks were thought to develop a sharper male head point at maturity, but a new analysis found that heads of both sexes became rounder as they grew. The change was stronger in females sampled from Biscayne Bay and Tampa Bay, Florida.
The study does not establish a universal growth rule or explain the head’s function. Young sharks were underrepresented, only two regions were sampled, and the researchers found no evidence that diet caused the shape change.
How were sharks compared?
Researchers measured front-edge curvature, length, sex and maturity with a minimally invasive catch-and-release method in two bays. Bonnetheads are small hammerhead relatives averaging roughly 70–85 cm in South Florida.
What changed from the old idea?
A 2005 hypothesis treated the male point as a maturity-linked sexual trait. Younger sharks of both sexes were sharper in the new data, with females rounding more as adults.
Was diet the cause?
Bonnetheads unusually digest seagrass as well as animal prey. Stable-isotope analysis did not link dietary niche to head shape, though limited sampling cannot rule it out.
Why does shape matter?
The cephalofoil may affect sensing, lift, turning and foraging. Age and sex may need to be included in future swimming and population comparisons.
What comes next?
More newborns, populations at other latitudes and embryonic development must be studied, along with direct tests of swimming and sensory performance.