Three-eyed gecko?

Alex Eben Meyer

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The CT scans of the ancient fossil—originally uncovered at Dinosaur National Monument—had been around for more than a decade. Researchers had long assumed it was an extinct relation of the modern skink. Dalton Meyer ’24PhD, a Yale graduate student in the earth and planetary sciences department, took a closer look. He saw something else.

Along with Chase Brownstein ’23, ’29PhD, a Yale undergraduate at the time, Meyer studied every bone, “each as its own item for analysis,” he says. “When we did that, it became clear that what we were looking at was pretty different.”

The fossil was, in fact, a gecko, which was surprising given the established timeline of lizards. Prior evidence had geckos showing up in North America about 50 million years ago, during the Eocene. This fossil came from sediment dating from the late Jurassic. In other words: it pushed back the arrival of geckos on the continent by at least 100 million years.

Of particular note was what’s known as a pineal opening, or parietal eye—essentially a third eye on the top of the skull. Present in some of today’s lizards, these third eyes have a retina and lens but no iris, so they cannot form complex images. Rather, they sense light, and are believed to track the daylight hours as a way to regulate physiologic processes. Modern geckos, which are nocturnal, no longer have this eye.

As the first to describe the species, Meyer was given naming rights. He landed on Helioscopos dickersonae. Helioscopos means “sun watcher.” Dickersonae is more personal; it honors Helen and Shirley Dickerson, Meyer’s late grandmother and great aunt, respectively.

Meyer hopes these findings shore up the value of fossils at a time when paleontology increasingly leans on DNA to sketch out the tree of life.