Four-eyed lizard roamed the Earth 49 million years ago, researchers say

When it comes to this ancient monitor lizard, the nickname "four eyes" is all too accurate. Scientists recently took a closer look at fossils of the reptile and discovered it had two extra eyes on top of its head.

The lizard, known as "Saniwa ensidens," was unearthed nearly 150 years ago in the Bridger Basin in southwestern Wyoming. But it wasn't until recently that scientists found -- using a computed tomography (CT) scanner -- that the ancient creature is the only known jawed vertibrate to roam the Earth with four eyes, according to a study published Monday in the journal "Current Biology."

“This tells us how easy it is, in terms of evolution, to self-assemble a complex organ under certain circumstances,” Yale paleontologist Bhart-Anjan Bhullar and co-author of the study told YaleNews. “Eyes are classically thought of as these remarkably complex structures. In fact, the brain is just waiting to make eyes at all times.”

Researchers from Yale and Germany's Senckenberg Research Institute teamed up to prove that the fourth eye suggests lizards may have evolved differently than other vertebrates, such as frogs and fish.

"Eyes are classically thought of as these remarkably complex structures. In fact, the brain is just waiting to make eyes at all times."

— Bhart-Anjan Bhullar, paleontologist

"This fourth eye confirms that the third eye in lizards is a parapineal derivative," the study explains. "The evolution of the pineal shows not only parallel reductions but also elaboration."

Most jawed vertebrates have a pineal organ, which researchers refer to as a "third eye" that acts as an internal clock. But many believe the lizard's third eye developed from another organ known as the parapineal -- and researchers are pointing to this study as proof.

“By discovering a four-eyed lizard, in which both the pineal and parapineal formed an eye on the top of the head, we could show that the lizard third eye really is different from the third eye of other vertebrates,” lead author Krister Smith, who works for the Senckenberg Research Institute, told YaleNews.

Using a CT scanner, researchers were able to more closely examine 1870s samples of the creature, which is approximately 49 million years old, and create 3D images to help them get a better look at their third and fourth eyes on top of the head.

"The CT scans showed that the ancient monitor lizard ... had spaces in its skull where a fourth eye would have sat," LiveScience reports.

The tests helped support researchers' theory that "pineal and parapineal eyes were not a pair of organs," YaleNews reports. However, more research needs to be done to determine how and when the lizard's third eye developed, researchers say -- and they plan to do just that.

“It’s important to recognize that there’s nothing mystical about the pineal and parapineal organs,” Smith said. “They can sense light and play a role in the endocrine system. However, some of the abilities conferred by the pineal are really quite extraordinary. For instance, some lower vertebrates can sense the polarization of light with the third eye and use this to orient themselves geographically.”