The old idiom "eyes in the back of your head" holds somewhat true for scalloped hammerhead and bonnethead sharks, according to new research that found these sharks possess a 360 degree field of vision. Virtually nothing can escape their view.
(Credit: Commander John Bortniak, NOAA)
"Everyone wants to understand why they have this strange
head shape," says Michelle McComb from Florida Atlantic University, who worked on the study. "Perhaps their visual field has
been enhanced by their weird head shape."
With colleagues Stephen Kajiura and Timothy Tricas, she fished
for juvenile scalloped hammerheads off Hawaii and looked for bonnethead sharks in
the waters around Florida. The sharks were quickly transported back to the lab so McComb's team could test the catch's field of vision.
Like optometrists, the researchers swept light in front of each shark's eyes. But as they did so, they recorded the eye's electrical activity. When compared to other sharks with odd-shaped heads, the scalloped hammerhead turned out to have the highest measurements. Here's the list of super see-ers, in order based on their visual skills:
#1. Scalloped hammerhead
#3. Lemon shark
Other tests revealed the scalloped hammerheads and bonnetheads also possess stereo rear-view vision and incredible depth perception. Part of this is due to their head shapes. It's a given that we humans have the brain and other matter located behind our eyes. For hammerheads, it's as though their rotating eyes are stuck on either side of a horizontal pole with nothing to block their sight.
"When we first started the project we
didn't think that the hammerhead would have binocular vision at all. We
thought no way; we were out there to dispel the myth," says McComb, who added that she heard about such "myths" on TV shows. Probably at Discovery.
You can watch a teaser video from a Shark Week program about hammerheads here. I believe it's leading to information about the shark's electric sensors, also located in the head.