How hammerheads grow their hammers

How hammerheads grow their hammers

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Researchers provide a unique glimpse into the development of the hammerhead sharks' iconic skulls, shedding some light on these oceanic marvels.

Baby hammerhead during development with a nascent hammerhead snout.
Baby hammerhead during development with a nascent hammerhead snout.

In an unprecedented study, scientists from the University of Florida (UF) have delved into the development of hammerhead sharks' skulls, uncovering the process behind their iconic hammer-like shape at the embryonic stage.

Led by UF professor Gareth Fraser, the study focussed on bonnetheads, the smallest among the hammerhead shark species. The species’ abundance in the Gulf of Mexico and the Atlantic Ocean, along with their near-shore presence, made them ideal subjects for the study.

Dramatic emergence

Using a series of images, the study chronicles the astounding transformation that occurs approximately halfway through the gestation of two-inch-long bonnethead shark embryos.

During this pivotal stage, their skulls undergo a dramatic expansion, pushing their still-developing eyes into unnatural positions. In subsequent weeks, the front of the hammerhead gradually rounds out, shifting backward towards the gills, ultimately giving rise to the distinctive shovel-like shape.

The findings of the study were published in the journal Developmental Dynamics.

Challenges faced

Studying hammerhead sharks is a challenge. They give birth to live young, hence it is difficult to observe the development of their embryos. In addition, many hammerhead species are endangered, so the harvesting of sharks for the purpose of studying their young is prohibited.

For this study, the researchers collaborated with partners and gained access to embryos preserved from bonnetheads caught in other biological studies. 

Due to the difficulty of studying hammerhead sharks, the scientists said that such an opportunity to study hammerhead sharks may never arise again.

“This is an insight into the development of a wonder of nature that we haven’t seen before and may not be able to see again.”
University of Florida Professor of Biology Gareth Fraser

The future

This study sets the stage for future experiments aimed at unraveling the mechanisms behind the hammerhead's control over their head shape and the evolutionary significance of their distinctive features. These features are believed to enhance their field of vision and their ability to detect the electrical movements of prey.

University of Florida