Friday, April 6, 2018

Fourth Eye Discovered Behind Third Eye

Senckenberg scientists 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 is published today in the journal "Current Biology".

It is present in many lizards and the New Zealand bridle lizard: the crown eye, also known as the "third eye" or parietal organ. "An eyelid was regularly formed in the Paleozoic vertebrates more than 250 million years ago," explains Dr. Krister Smith from the Senckenberg Research Institute in Frankfurt and head of the study.

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.

A fourth eye was discovered on the fossil waran. 
Photo: A. Lachmann / Senckenberg Society for Nature Research /

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 the lizard 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, "explains Smith.In their study, the researchers therefore 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 were to get teeth again," adds Smith.

The particular development of the laryngeal organs also has consequences for future research. Smith says: "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. "Contact

Contacts and sources:
Dr. Krister T. Smith
Senckenberg Research Institute and Nature Museum Frankfurt

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