‘ Extinct monitor lizard had 4 eyes’

Berlin, April 3: An extinct species of monitor lizard had four eyes, a first among known jawed vertebrates, a fossil study has found.

Today, only the jawless lampreys have four eyes, according to researchers at Senckenberg Research Institute in Germany.

The third and fourth eyes refer to pineal and parapineal organs, eyelike photosensory structures on the top of the head that play key roles in orientation and in circadian and annual cycles. The findings elucidate the evolutionary history.

The photosensitive pineal organ is found in a number of lower vertebrates such as fishes and frogs, they said.

It is often referred to as the “third eye” and was widespread in primitive vertebrates.

“On the one hand, there was this idea that the third eye was simply reduced independently in many different vertebrate groups such as mammals and birds and is retained only in lizards,” said Krister Smith from the Senckenberg Research Institute.

“On the other hand, there was this idea that the lizard third eye developed from a different organ, called the parapineal, which is well developed in lampreys ,” Smith said.

By discovering a foureyed lizard — in which both pineal and parapineal organs formed an eye on the top of the head — the researchers confirmed that the lizard third eye really is different from the third eye of other jawed vertebrates.

Smith and his colleagues got the idea that the fossilised lizards might have a fourth eye after other experts came to contradictory conclusions about where the lizard’s third eye was located.