Scientists discover chameleon’s telephone-cord-like optic nerves once overlooked by Aristotle and Newton
Chameleons’ wandering eyes have fascinated and puzzled scientists since the days of ancient Greece. Now, after millennia of study, modern imaging has revealed the secret of their nearly 360-degree view and uncanny ability to look in two different directions at once. Behind their bulging eyes lie two long, coiled optic nerves — a structure not seen in any other lizard.
“Chameleon eyes are like security cameras, moving in all directions,” explained Juan Daza, associate professor at Texas’ Sam Houston State University and author of a new study describing the trait. “They move their eyes independently while scanning their environment to find prey. And the moment they find their prey, their eyes coordinate and go in one direction so they can calculate where to shoot their tongues.”
The chameleon’s darting eyes are easy to observe, but scientists have never fully understood the optic nerve that makes such movement possible. Edward Stanley, director of the Florida Museum of Natural History’s digital imaging laboratory, was visiting Daza’s lab in 2017 when he first spotted the unique shape in a CT scan of the minute leaf chameleon (Brookesia minima). The coiled optic nerves were unlike anything he’d seen before.
Still, both scientists were initially cautious. Chameleons have been studied for millennia; surely, they were not the first to make this discovery.
“I was surprised by the structure itself, but I was more surprised that nobody else had noticed it,” Daza said. “Chameleons are well-studied, and people have been doing anatomical studies of them for a long time.”
Chameleons are native to Africa, Europe and Asia. Beyond their color-shifting skin, the lizards have an impressive repertoire of tree-dwelling traits. They use their grasping tails to steady themselves and their oven-mitt-shaped feet to creep along branches with a slow, deliberate gait. Chameleons have no need to rush because they have a ballistic tongue, which can go from zero to 60 miles per hour in just a hundredth of a second. This long, sticky tongue can shoot distances over twice the length of the chameleon’s own body to snatch up unsuspecting prey.
Charismatic and unique, it’s no wonder that chameleons have long captured human attention. Their distinct form and curled tail are even distinguishable among ancient Egyptian petroglyphs. Convinced there must be a published description of these coiled optic nerves out there, the team went deep into the stacks of research in search of evidence, even bringing in language experts to decipher old texts published in French, Italian and Latin — and sometimes a confounding mix of multiple languages.