We forgive anyone doing a double-double-take at Saniwa ensidens, a fossil monitor lizard excavated over a century ago that now appears to have had four peepers. Jeepers!

Four-Eyed Lizard, Saniwa ensidens

Forty-nine million years ago, an otherwise unremarkable monitor lizard shuffled off this mortal coil in what is now Fossil Butte National Monument in southwestern Wyoming. One hundred and forty-nine years ago, dinosaur hunters digging in the Green River Formation unearthed the creature's remarkably preserved bones, dubbed it “Saniwa ensidens,” and unceremoniously consigned the remains to obscurity in a museum drawer.

That's where the story would have ended, if not for some curious researchers who fortuitously decided to take another look at not one, but two specimens of this roughly four-foot-long lizard. Their advantage over the 1871 diggers lies in their tools: detailed x-ray scans generated through computerized tomography.        

Four-Eyed Lizard, Saniwa ensidens

What they discovered will shock- er, sorry for almost employing an irritating internet clickbait cue. Instead, we'll quote the title of their report published in Current Biology: “The Only Known Jawed Vertebrate with Four Eyes and the Bauplan of the Pineal Complex”. Shocking, huh?

Well, kinda... the title's last seven words dim the luster of the first eight. To be more exact, those extra eyes aren't duplicates of the critter's “normal” pair of peepers. Instead, they're what's called pineal and parapineal organs. Some modern turtles, lizards and fish have a third such “eye” on top of their heads, thought to be a sense organ for their inner biological clocks. Give Saniwa ensidens its due, however: with a pair of para-optic organs at work, its biological clock must have run like a well-snake-oiled machine. (via ScienceMag, image via opacity)

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