Ancient Lizard Had Four Eyes

An Ancient Lizard Had Four Eyes But We Don't Know Why

And no, it wasn't just wearing dorky glasses.

By David Grossman
SENCKENBERG GESELLSCHAFT FÜR NATURFORSCHUNG / ANDREAS LACHMANN / DIGIMORPH.ORG

Researchers have discovered a new ancient lizard with a remarkable adaptation: four eyes. It's the first known jawed vertebrae to have the distinct feature.

The extinct Saniwa ensidens, a monitor lizard, lived around 34 million years ago. It had two eyes where lizards normally have eyes, but on the top of its head rested structures known as a pineal organ and a parapineal organ which likely helped it keep tabs on the changing seasons and its own orientation. These aren't eyes as we know them. They don't blink and mainly signal the existence of light.


No jawed lizard has ever been discovered to have both pineal and a parapineal eye. "In order most easily to redevelop into a lens-bearing eye in Saniwa ensidens," the researchers from the Senckenberg Research Institute and Yale say in their paper discussing the creature, "the ancestral pineal organ must have had some latent photoreceptive capability or a structural predisposition to photoreceptivity."


The lizard’s skull. Its pineal and parapineal eyes would be in the greyed-out areas in A.
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What purpose the fourth eye served in addition to pineal eye is hard to say. The organs aren't a working duo like eyes typically function, they acted independently of each other. Researchers are still trying to figure out why most lizards have lost their third eye in the evolutionary process, it's possible that the Saniwa ensidens fourth eye plays a role in that story.

“We only know that the ancestors of major land-vertebrate groups all had a third eye,” Krister Smith of Senckenberg and lead author of the paper, tells Gizmodo. “If we want to understand the course of its evolution, then we need to know when the parapineal assumed its present role, as in lizards.”

Source: Gizmodo