Diversity of lizards in Cretaceous amber fossils. Image: Courtesy of David Grimaldi, additional photos by Kristen Grace, Florida Museum of Natural History
Some 99 million years ago, a rich diversity of lizard species foraged in the tropical forests of what is now Myanmar. The vast majority vanished without a trace; their fragile remains rapidly recycled by an opportunistic environment. But occasionally, these arboreal creatures were subsumed by floods of resin, exchanging their lives for preservation in the fossil record’s eerie amber snapshots of bygone ecosystems.
Now, scientists have been granted access to twelve of these sepia-toned Cretaceous tableaus, which had been hitherto cloistered away in private collections. The specimens were recently donated to the American Museum of Natural History (AMNH), and reveal many “missing links” in lizard evolution according to Edward Stanley, a postdoctoral researcher in herpetology and co-author of a study on the specimens published Friday in Science Advances.
"These fossils tell us a lot about the extraordinary, but previously unknown diversity of lizards in ancient tropical forests,” said Stanley in a statement.
“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.”
This is especially true given the extraordinary condition of the fossils. Fine details like scales, skin pigments, and soft tissue are frozen in these amber coffins, providing an unprecedented glimpse of a bygone ecosystem.
“Usually we have a foot or other small part preserved in amber, but these are whole specimens—claws, toe pads, teeth, even perfectly intact colored scales,” Stanley said.
Even in cases of bodily decay, Stanley and his colleagues were able to digitally reconstruct the anatomies of the lizards using micro-CT scanners and 3D-printing printers. This approach yielded a host of new insights about the evolutionary origins and trajectories of multiple lizard groups.
For instance, the specimens include the oldest chameleon ever found, beating out the previous contender by a whopping 75 million years. The intricate remains of adhesive gecko toe pads reveal that this animal’s climbing abilities took hold way back in the evolutionary timeline, earlier than previously assumed.
But more broadly, the specimens demonstrate that the tropical forests of the Cretaceous were as rich in lizard diversity as modern equatorial jungles. Not only does that provide perspective on the origins and past evolution of lizards, it also spotlights their future on the planet, which is increasingly at risk due to human activity.
“[T]he tropics are not impervious to human efforts to destroy them,” Stanley concluded. “These exquisitely preserved examples of past diversity show us why we should be protecting these areas where their modern relatives live today.”