The world's oldest known tropical chameleon has been discovered in a piece of amber from Myanmar in Southeast Asia. The fossil, about 100 million years old, dates back to the middle of the Cretaceous period, when massive dinosaurs roamed the Earth. Researchers say that it is about 78 million years older than the previous oldest chameleon on record.
This dime-sized chameleon was found among 11 other ancient fossil lizards from collections at the American Museum of Natural History. As tropical forest-dwellers, this tiny lizard may have been scurrying away from large predators or hunting for arthropods when it crawled into the sticky resin of a coniferous tree, which has fossilized into amber over time.
Previously, not much was known about small tropical lizards, as they have fragile bones that do not preserve well when buried in sediment like the bones of dinosaurs. Researchers say that the new collection may include the ancestors of geckos and chameleons and, therefore, shed light on the evolutionary history of lizards.
"These fossils tell us a lot about the extraordinary, but previously unknown diversity of lizards in ancient tropical forests," co-author Edward Stanley, a University of Florida postdoctoral student in herpetology at the Florida Museum of Natural History, said in a news release. "The fossil record is sparse because the delicate skin and fragile bones of small lizards do not usually preserve, especially in the tropics, which makes the new amber fossils an incredibly rare and unique window into a critical period of diversification."
Using a micro-CT scanner, researchers carefully analyzed the amber fossils and pieced together the tiny bones and soft tissues. Of the 12 lizard specimens, three -- a gecko, an archaic lizard and the chameleon -- were particularly well preserved. However, they have yet to be named.
"It was mind-blowing," Stanley said about seeing the fossils for the first time. "Usually we have a foot or other small part preserved in amber, but these are whole specimens-claws, toepads, teeth, even perfectly intact colored scales. I was familiar with CT technology, so I realized this was an opportunity to look more closely and put the lizards into evolutionary perspective."
Discovering the 100 million-year-old chameleon challenges the view that these animals first evolved in Africa. It also helps researchers pinpoint the evolutionary order of some of the lizard's most distinctive features.
For example, the amber-trapped lizard has the iconic projectile tongue of modern chameleons, but it had not yet evolved the unique body shape and fused toes adapted for gripping.
The ancient lizards have modern counterparts living in the same region, suggesting that the Cretaceous tropics were as diverse and lizard-friendly as they are today and have remained fairly stable without the impacts of human activity.
"These exquisitely preserved examples of past diversity show us why we should be protecting these areas where their modern relatives live today," Stanley added.
Their findings were published in the March 4 issue of the journal Science Advances.
