Phenomenal sensory organ Fossil lizard had four eyes

Researchers discover lizard with four eyes

It has been known for a long time that there are lizards with three eyes. In the bridge lizard, the additional sense organ sits centrally on the skull plate and serves to perceive brightness differences. A very long time ago there was even a lizard with four eyes, as researchers have now found out.

Extraordinary sensory achievements in the animal kingdom

The sense organs provide services that often seem unimaginable. For example, the human nose perceives over a trillion odors. In the animal kingdom, the senses are often much sharper. For example, dogs can not only hear much better than humans, but also smell much better. Other animals can see very well. For example, the outstanding visual achievements of birds of prey with the proverbial "eagle eye" have found their way into the general consciousness. At least as impressive is what frogs are capable of: they can even see colors in the dark. And the bridge lizard has a third eye that serves to perceive brightness differences. A very long time ago, there was a lizard that even had four eyes. Researchers at the Senckenberg Research Institute have now discovered this.

An international research team has provided evidence for a four-eyed lizard. They were able to show that the extinct waran in his lifetime had behind the so-called "third eye" another sense organ. (Photo: Senckenberg Gesellschaft für Naturforschung)

First evidence for a four-eyed higher vertebrate

As the Senckenberg Gesellschaft für Naturforschung reports in a communication, scientists from the Senckenberg Research Institute have provided evidence for a four-eyed lizard with an international team.

Based on the extinct species Saniwa ensidens, they show that the waran had another sensory organ behind the so-called "third eye" during his lifetime. They thus provide the first evidence of a four-eyed higher vertebrate.

The study was published in the journal "Current Biology".

Regressed in the course of evolution

Many lizards and the New Zealand bridle lizard have it: the crown eye, also known as the "third eye" or parietal organ.

"A crown-eye was regularly formed in the vertebrates of the Paleozoic over 250 million years ago," explains study lead dr. Krister Smith from the Senckenberg Research Institute in Frankfurt.

He goes on to say: "The history of the apex seems to have been quite simple so far: we assumed that this organ has regressed in the course of evolution in all higher vertebrates except the lizards."

This regression was accompanied by a change of function to the pineal gland. However, according to the latest findings of the US-American-German team around Smith, this does not seem to have been the case: the fossil Waranart Saniwa ensidens they examined even had another crude fourth eye organ behind the third eye.

About 49 million years old

The Eocene Waran fossil of North America is about 49 million years old and up to 1.30 meters long.

On its head are the two additional sensory organs in a midline position one behind the other on the skull. The position of both eyes contradicts the classical, paired model of the pineal gland.

"We therefore assume that the usual 'third eye' of lizards has nothing to do with the pineal gland. The pineal gland, from which the fourth eye developed, is still present in lizards, but is inside the skull, as in mammals, "said Smith.

Lizards occupy a special position

In their study, the researchers therefore also speak of a "re-evolution": An occurrence of already disappeared features after a very long time.

"It would be a similar process, for example, if our birds today had teeth again," adds Smith. The special development of the eyes in lizards also has consequences for the upcoming research.

"It turns out that the evolution of these two organs - the pineal gland and the eyeball - is more complex than previously thought. We think that lizards have a special place in the development of the eyes and therefore should not - as before - serve as model organisms for other vertebrates, "said Smith. (Ad)