Fossils reveal ancient four-eyed lizard species •

For the first time, researchers have identified a jawed vertebrate with four eyes. The discovery that an extinct species of monitor lizard had third and fourth eyes will give scientists new insight into the evolution of eye-like structures on the top of the head known as pineal and parapineal organs. .

The pineal and parapineal organs play an important role in orientation, circadian rhythm and annual cycles. The researchers explained that the photosensitive pineal organ, often called the third eye, is found in many lower vertebrates such as fish.

Krister Smith at the Senckenberg Research Institute in Germany is one of the co-authors of the study.

“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 only retained in lizards among fully terrestrial vertebrates,” said said Smith.

“On the other hand, there was this idea that the lizard’s third eye developed from a different organ, called the parapineal, which is well developed in lampreys. Those two ideas weren’t really consistent.

“By discovering a four-eyed lizard – in which the pineal and parapineal organs formed one eye on the top of the head – we were able to confirm that the third eye of the lizard is truly different from the third eye of other jawed vertebrates,” said explained Smith.

Conflicting reports about the location of the third eye on fossilized lizards have led researchers to investigate. They obtained museum specimens that had been collected nearly 150 years ago at Grizzly Buttes and performed CT scans.

The study found that two different fossilized lizards had space not only for a third eye, but also for a fourth eye.

Research confirms that the pineal and parapineal glands were not a pair of organs like vertebrate eyes are. The result of this investigation also suggests that the third eye of lizards evolved independently from the third eye of other vertebrate groups.

Smith pointed out that these fossils, which had been lying around in a museum for more than a century, had hidden value.

“The fossils that we studied were collected in 1871, and they’re pretty scrappy — really badly weathered,” Smith said. “One would be forgiven for looking at them and thinking they must be useless. Our work shows that even small fragmentary fossils can be extremely useful. »

The study is published in the journal Current biology.

By Chrissy Sexon, Personal editor

Image Credit: Senckenberg Gesellschaft für Naturforschung / Andreas Lachmann /

Comments are closed.