In Burmese- Myanmar, the fossilized lizard found preserved in amber dates back some 99 million years, U.S. scientists have determined, making it the oldest specimen of its kind and a “missing link” for reptile researchers.
The gecko captured in amber was shown to possess adhesive toe pads similar to those found in its modern-day descendants
Now, scientists sifting through museum collections have described a dozen of these pint-sized reptiles all entombed in amber. The hapless lizards were caught in the sticky resin of ancient coniferous trees and remained suspended until the present day—several in exquisite condition with claws, bones, teeth, toe pads and even scales intact. These spectacular fossils give scientists a peek into life of the diminutive denizens of the mid-Cretaceous.
The fossils were actually discovered decades ago in a Burmese mine but remained in private collections until their recent donation to the American Museum of Natural History, which gave scientists access for study. Using CT scanners to image the fossils, the researchers could “digitally dissect” the lizards without harming the amber droplets, says postdoctoral student Edward Stanley, co-author of the new paper.
The gecko was shown to possess adhesive toe pads similar to those found in its modern-day descendants. This suggests the adaptation dates back more than 100 million years. The archaic lizard was not yet formed into the distinctive shape of today’s animals, but was adorned with the distinctive darting tongue seen in contemporary specimens. The chameleon found preserved in the amber revealed that these creatures likely did not get their start in Africa as previously believed.
The set includes creatures similar to modern-day geckos and chameleons, as well as a range of species that sport a mash-up of features from both ancient and modern reptile relatives, according to the study published Friday in Science Advances. These animals help fill in the patchy evolutionary history of pint-sized lizards.
“This diverse lizard assemblage shows that back in the day, the tropics were as lizard-friendly as they are today,” says Stanley.
Such wide variation is not necessarily unexpected, says Kevin de Queiroz, curator of the reptile and amphibian collection at the Smithsonian’s National Museum of Natural History. “There’s a fair amount of diversity in the tropics now,” he says. “So it’s not too surprising that they’ve been diverse in the past.”
Even so, capturing this diversity in the fossil record is less common, says de Queiroz. The fossil record is strongly biased to large animals living in particular environments that can preserve creatures after their death, like deserts or riverbeds. The damp, hot climate in the tropics rarely preserves small and delicate fossils—unless the unfortunate creatures become trapped in tree resin. This ancient group therefore paints a much more complete picture of minute mid-Cretaceous reptiles than scientists have seen before.
One of the reptiles, a dime-sized baby relative of the chameleon, is the oldest discovered representative of that lineage, beating out the previous title-holder by nearly 80 million years.
Chameleons’ closest relative is the agamidae—a group that includes the bearded dragon lizards. Based on genetic evidence, chameleons were thought to have split from these relatives around the mid-Cretaceous period, but fossil evidence from this time had been lacking until now.
Small reptiles have delicate bodies and typically deteriorate quickly, he said. Being encased in solid amber helped to lock the specimen together.
Stanley and other researchers used high-resolution digital X-ray technology to examine the creatures and estimate the age of the amber without breaking it.
the lizards most likely stepped into the amber in its more resinous form, were trapped and eventually covered by the clear goo as it flowed from the trees. Aside from the dozen examples of lizards -both nearly complete and in pieces- the researchers found insects and bits of vegetation. While there are till gaps in the knowledge pool about life in the Cretaceous, this newly mined vein of information gives a clearer picture of the lost world of 99 million yeas ago.