Bonnethead sharks, known for their uniquely shaped heads, are part of the hammerhead shark family. For years, there was thought to be only one species, Sphyrna tiburo, with two subspecies. One is found in the western Atlantic, including the waters off the US, Mexico, and the Bahamas, and the second is found in the eastern Pacific. However, new findings suggest a more complex picture.

Two distinctly different species

The study, which analysed 23 bonnethead sharks from the US and Belize, focused on their physical characteristics and genetic makeup. Researchers found significant differences in the number of vertebrae: sharks from Belize had 80 to 83 vertebrae, while those from the US had only 71 to 74 vertebrae. These differences were not only seen in the vertebrae, but also in the shape of the sharks’ distinctive heads. Sharks from Belize had a more pointed, shovel-shaped head compared to the US sharks, which had a broader, more rounded shape.

DNA confirmation

In addition to the physical differences, DNA analysis confirmed that these sharks are genetically distinct from one another. Researchers used both mitochondrial DNA and nuclear microsatellite markers, which further separated the two populations.

A new species!

As a result of these findings, the study proposes that the two groups should be recognised as separate species. The new species, named Sphyrna alleni (after Paul G. Allen, a key contributor to the research), is distinguished by its distinctive head shape, vertebral count, and genetic markers. The study also suggests that more research is needed to clarify the status of the bonnethead sharks found in the eastern Pacific.

This discovery highlights the importance of genetic and morphological studies in understanding biodiversity and may lead to a re-evaluation of how we classify sharks across the globe.