Lizard fossils provide snapshots of evolution

Researchers say one of the tropical creatures, apparently a very early chameleon, was caught in the resin of a coniferous tree in present-day Southeast Asia.

The specimen, along with 11 other fossilized lizards, was found preserved in amber in a mine decades ago. However, it was only recently that specialists had the chance to look at them properly.

Scientists say the fossils provide snapshots that reveal "missing links" in the evolutionary history of lizards.

Three of the fossils - of a gecko, an archaic lizard and a chameleon - were particularly well-preserved.

"These fossils tell us a lot about the extraordinary, but previously unknown diversity of lizards in ancient tropical forests," said Edward Stanley, a herpetologist at the Florida Museum of Natural History, and co-author of a #link:http://advances.sciencemag.org/content/2/3/e1501080.full:new study in the journal "Science Advances."#

Stanley's attention was drawn to the fossils after a private collector donated them to the American Museum of Natural History. He hit upon the idea of using computerized tomography - taking a series of cross-sectional X-rays - to study the creatures' remarkably preserved bodies. The researcher gleaned much-needed clues as to how various species of reptiles emerged from common ancestors.

"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," said Stanley.

"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."

The fossils were compared in detail to existing and extinct lizards.

Examining one, Stanley was able to determine it was that of a chameleon that dated back tens of millions of years farther than previous examples. Research on the amber gecko showed it had evolved adhesive toepads far earlier than previously thought. The various species are to be named and described in greater detail in a future study.

According to Stanley, the find demonstrates the value of stable natural habitats, with many of the ancient lizards' ancestors living in the tropics.

"These exquisitely preserved examples of past diversity show us why we should be protecting these areas where their modern relatives live today," Stanley said.

"The tropics often act as a stable refuge where biodiversity tends to accumulate, while other places are more variable in terms of climate and species. However, the tropics are not impervious to human efforts to destroy them."