Scientists discover 99-million-year-old lizards preserved in amber.
By Eva Botkin-Kowacki, MARCH 5, 2016
A lizard preserved in amber from Myanmar forests.
Courtesy of David Grimaldi
Amber fossils give scientists clues into lizard evolution.
Some 99 million years ago, 12 unsuspecting lizards stepped
or fell into sticky tree resin and couldn't tear themselves loose
in the forests of what is now Myanmar. Over time that resin
fossilized into amber, preserving the little lizards for scientists
to study later.
Now, researchers are looking to these prehistoric golden
chunks to better understand how lizards have evolved.
There was a diverse population of lizards living in the region
at the time, the scientists report in a new paper published Friday
in the journal Science Advances. And they run the gamut, with some
quite similar to modern lizards – like geckos, wall lizards, and
dragon lizards – and others like nothing known today.
Chameleon preserved in mid-Cretaceous amber.
Courtesy of David Grimaldi
"The assemblage is cool because it has some examples which are
really, really modern and then others which are really, really old,
and then others in between," study co-author Edward Stanley, a herpetology
researcher at the Florida Museum of Natural History, tells The Christian
"In the amber we have things that are clearly gecko," says Dr. Stanley.
The gecko-like prehistoric specimens have toe pads. Modern geckos use their
toe pads to scale walls and perform other sticky-footed feats, but these
prehistoric toe pads appear somewhat different.
Other amber-preserved lizard specimens had been found with toe pads more
similar to those on living geckos, which suggests that "even 100 million years
ago geckos apparently already had evolved a well-diversified subset of tools
for clinging onto surfaces," Stanley says.
Lizards preserved in mid-Cretaceous amber.
Courtesy of Daza et al. Sci. Adv. 2016; 2 : e1501080
Another block of amber could show "some kind of animal that was on the road
to becoming a chameleon," Stanley says. And that specimen, at less than half an
inch long, had probably just hatched before it met its demise.
A CT scan of the itty-bitty specimen revealed a skeleton similar to those of
modern chameleons but also with features more like other lizards. "It's this
interesting sort of halfway stop between a modern chameleon and the sister
group to chameleons, which are the dragon lizards," Stanley says.
This specimen doesn't have the fused digits that today's chameleons have to
help them live in trees. But, like a chameleon, it has a shorter spine with
fewer vertebrae than its cousin lizards. It also has a characteristically long
hyoid bone, the long bone in chameleon's throats that they use to shoot their
sticky tongues out at top speeds to capture unsuspecting prey.
These fossils can also offer other clues into the lizards' lives. Amber, because
it is produced from tree resin, can only form in forested regions, so the animals
must have been spending a lot of time around trees.
Amber can also preserve things when other processes cannot. The Myanmar forest amber is a good
example because it's warm and moist in a tropical forest so things decompose quickly, Stanley
explains. But something trapped in resin is not affected in the same way.
Amber is also good at preserving small things, like bits of plants, insects and other small
animals, that might otherwise get lost in the fossil record. And it can preserve more of the
organism, as it freezes it in place almost exactly how it lived, tissue and all.
How does it work?
"It's a process of natural fixatives in the resin," George Poinar, an entomologist at
Oregon State University known for his research on amber fossils who was not part of this
study, tells the Monitor. "[The resin] contains preservatives that enter into the tissue,
" he explains. "At the same time, the sugars in the resin withdraw moisture from the specimen."
Those two processes preserve the tissue of the organism as the amber hardens around it.
Dr. Poinar, who admits to having a "fertile imagination," was intrigued by the fact that
although there were many different types of lizards frozen in time, many of the specimens
were incomplete. He proposes that perhaps the lizards were stuck in the resin in a mad dash
to escape a carnivorous dinosaur looking for a tasty morsel.
In Poinar's scenario, vicious, agile, clawed dinosaurs chased the lizards up a tree. When
the lizards became ensnared in resin, the hungry dinosaur would have snacked on them,
leaving behind the parts that would mean also eating the sticky goop.
"This is just speculation on my part," Poinar says. But, he adds, it could explain why
so many of these lizards appear to be tree-dwellers while many of them live on the ground today.
The Christian Science Monitor.