Scientists have found that an ancient species was a proud owner of two sets of eyes - an extinct monitor lizard. This is the first time that a terrestrial animal has been found to have such a number of eyes.

Today only the jawless lampreys have four eyes.

Jawed Vertebrates

A study published in Current Biology shows that the second pair of eye-like organs were found on a fossil from the 19th century.

The eyes found on the ancient monitor lizard are not really eyes in the conventional sense of the word. They are called pineal and parapineal organs. They are eye-like photosensory organs found at the top of the head. These organs are responsible for helping with orientation, and with circadian and annual cycles. Pineal organs can also still be found in frogs and fishes.

This ancient monitor lizard lived in what is now Wyoming and Scientists have named it Saniwa ensidens.

The discovery was made by reexamining Saniwa ensidens fossils that were found in Wyoming in 1871. To find these new organs, scientists used detailed x-ray scans using computerized tomography. This revealed two holes at the top of its skull.

These findings could show that the lizards developed their pineal organ differently than other animals which have the presence of a pineal organ.

Figuring Out The Third Eye

Researchers just chanced upon this discovery. At first, the reexamining of the fossil had nothing to do with finding the other set of eyes on the monitor lizard. There was debate among researchers of where the third eye of the lizard was located. Then the researchers realized that there may actually be a fourth eye which had been sparking debate about the location of the pineal organ.

Scientists explored the idea of the lizard having the fourth eye but didn't expect to find another organ. They found the third and fourth holes for the pineal and parapineal organ in two separate fossils discovered in Wyoming almost 150 years ago.

These findings show scientists that the organs were not like standard eyes, and this evidence shows that pineal organs in lizards evolved independently of other animals. Pineal organs allow animals to sense the polarization of light to orient themselves.

Animals such as turtles, lizards, and fishes have pineal organs. Jawless lampreys are the only living vertebrate with four eyes, and Saniwa ensidens is the only other vertebrate known to have four eyes.