four-eyed prehistoric lizard
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Credit: Senckenberg Research Institute 

A prehistoric lizard with four eyes actually existed

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Apr 5, 2018

Godzilla may have atomic breath, but he still doesn’t have the extra advantage of a 50-million-year-old monitor lizard that was crawling around during the Eocene era.

Saniwa ensidens had four eyes. Literally. Researchers from Yale University and Senckenberg Research Institute in Germany recently unearthed evidence of pineal and parapineal eyes on this species, which functioned as light sensors, when examining fossils of long-extinct lizards. What may seem bizarre to anyone else is something they long suspected.

Third eyes were not uncommon among prehistoric vertebrates. The pineal gland, an endocrine gland in vertebrate brains that produces melatonin to regulate sleep cycles, is often looked at as a third eye if it has a lens and retina (though it’s nowhere near as obvious as a horror-movie eyeball). While extra eyes vanished from most higher vertebrates as they evolved, they still exist in some species of frogs and fish, like the jawless lamprey, which looks like it emerged from a Guillermo del Toro movie. What hadn’t been proven ever to have existed in a vertebrate with jaws before—until now—was that freaky fourth eye.

“It’s important to recognize that there’s nothing mystical about the pineal and parapineal organs,” said Krister Smith of the Senckenberg Institute, who recently published a study in the journal Current Biology. “They can sense light and play a role in the endocrine system. However, some of the abilities conferred by the pineal are really quite extraordinary. For instance, some lower vertebrates can sense the polarization of light with the third eye and use this to orient themselves geographically.”

skull of a prehistoric four-eyed lizard

Credit: Senckenberg Research Institute

That sounds paranormal enough, but it’s really all biology. Smith believes the fourth eye separates S. ensidens from its three-eyed brethren because the pineal and parapineal glands each formed a parietal eye on top of its head. CT scans allowed the researchers to study fossil fragments of the lizard, which revealed that the pineal and parapineal eyes developed independently instead of double-spawning from just one organ.

“This tells us how easy it is, in terms of evolution, for a complex organ to self-assemble under certain circumstances,” said Yale paleontologist Bhart-Anjan Bhullar, who co-authored the study with Smith and colleagues Gunther Köhler and Jörg Habersetzer. “Eyes are classically conceived of as these remarkably complex structures. In fact, the developing brain is just waiting to make eyes given the right signals.”

When exactly third (and fourth) eyes appeared in lizards is still unknown. More research needs to be done on what scientists call the “lizard shift.” Bhullar noted the eye is an extension of the brain, which has the power to change the development of embryonic skin it comes into contact with, setting off what he calls a “self-sustaining molecular cascade” that will form a lens and retina in that tissue and give a lizard its third eye before it even hatches. The brain of S. ensidens obviously didn’t stop there.

While we don’t know of any four-eyed lepidosaurs creeping around, if you see a weird spot on top of a lizard’s head, you now know what it is.

(via Yale News)

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