New Haven Register (Sunday) (New Haven, CT)
Three-eyed gecko fossil ancestor unearthed by Yale paleontologists
Yale University paleontologists have discovered a previously unknown three-eyed gecko ancestor in fossil remains unearthed in Utah.
This is the oldest gecko fossil ever found on the continent, as the discovery places the arrival of geckos in North America much farther back than previously understood — roughly 163-145 million years ago.
The research team named the Jurassic period gecko after the lead researcher’s grandmother and great-aunt, but not because of the third eye.
The find was unusual for a number of reasons, lead study author Dalton Meyer, a Ph.D student at Yale said. But primarily this ancient gecko was uniquely different for having a parietal eye, a “third eye” on top of its skull that was used to sense light and darkness. Modern geckos don’t have that, in large part because they’re nocturnal.
“This new fossil specimen shows that there was more diversity in lifestyle in the early geckos or their relatives that we didn’t know about previously,” said Matthew Heinicke, a herpetologist at the University of Michigan Dearborn who studies gecko evolution.
Meyer named the new species Helioscopos dickersonae. The genus Helioscopos translates to “sun watchers.” Meyer chose the species name, dickersonae, to honor his grandmother Helen Dickerson, great aunt Shirley Dickerson, and Mary Dickerson (no relation) who was the first curator of herpetology of the American Museum of Natural History in New York City.
Helioscopos is not the direct ancestor of American gecko species. Meyer said that it’s likely what he discovered was a “ghost lineage.” The geckos we see today in America came from a separate migration event after the Jurassic period.
Meyer said the finding shows that the climate and geography of the Jurassic age were such that a tiny lizard group like geckos could spread all over the world. Small, non-flying animals tend to have a hard time migrating because they can’t move as far on their own. The presence of geckos in America and Europe at the same time in the Jurassic points to both land connections between the two continents, and large swathes of stable, similar habitat.
“Working on this fossil has really illuminated to me that not only are geckos a really ancient group, but from their earliest onset they were probably a pretty widespread group,” said Meyer.
The gecko skull had been unearthed with others as part of an earlier study in the Utah section of Dinosaur National Monument, which is run by the National Park Service and crosses over into Colorado. Originally it was thought to be a skull of a skink reptile. But because of its small size and extreme fragility it was never fully separated from the ancient sediment it was interred within.
As a result, the paleontologists had to get creative in order to study them. Using portable scanners they were able to create 3-D models of the entrapped skulls. Meyer and his colleagues then reconstructed the skulls digitally. One of the skulls was a skink, but the other one was the earliest gecko known to North America.
“We were able to examine these fossils in more detail than had ever been previously possible,” Meyer said of the process. “These fossils are so small you really can’t get them out of the rock, at some point the rock becomes necessary to keep things stable.”
Geckos are found on every continent except for Antarctica. They live in warm environments and typically eat insects. In many tropical areas, house geckos are willing, semiwild roommates of humans, feasting on mosquitos and other insect pests. Many geckos are nocturnal and prodigious climbers. DNA analysis indicates that the gecko toe has evolved and re-evolved 11 separate times across all gecko groups.
Environmentalists call them “charismatic” because of their adorable looks, and many species of gecko are sold on the international pet market.
Not much is known about the early evolutionary history of geckos. They’re thought to be one of the oldest groups of lizards, diverging from their lizard cousins sometime in the Jurassic, the middle period of the Age of Dinosaurs. Their fossils first appear in Jurassic-aged rocks, and they are thought to have first appeared somewhere in Asia.
But the fossil record is not kind to geckos. As tiny lizards, they don’t readily fossilize. After death their bones are much more likely to break down than those of larger animals, crushed to dust or dissolved in acidic water.
“Because of the paucity of the fossil record it is difficult to pin down the exact places where they lived in the distant past,” Heinicke said.
For a gecko to fossilize, very special conditions need to be in place. Gecko feet, complete with sticky toepads, have been found preserved in Cretaceous Era amber. Some of the most complete gecko fossils come from the same islands off the coast of Germany that held the feather fossils of bird ancestor, archeopteryx. Other ancient gecko specimens have been found in the Gobi Desert.
After reconstructing the Utah fossil, Meyer and his co-authors found that the skull had a lot of features of modern geckos, despite its third eye, and a lot of similarities to fossilized European geckos.
“At the time, 150 million years ago, North America and Europe were very closely linked,” said Heinicke. “The North Atlantic Ocean hadn’t really opened up yet, so this matches the pattern that has been observed in other reptiles, like dinosaurs … it fits the puzzle of geographic patterns pushing way back into the past.”