By Dr. Becker
More than 70 million years ago, a group of lizards living in the tropical forest area of what is now Myanmar had their lives cut short. They fell or otherwise crawled into the sticky resin of a coniferous tree and were preserved there, as the resin fossilized into amber, for millions of years.
Fossilization is rare in tropical forests because of the moist environment, but amber is the exception. Researchers have been able to study the rare find, which includes 12 lizards in all, to reveal a glimpse into what types of creatures lived in the "poorly preserved but potentially diverse mid-Cretaceous paleotropics."1
The Oldest Known Lizards Preserved in Amber
A private collector donated the amber samples to the American Museum of Natural History, where Edward Stanley, Ph.D., a researcher in herpetology at the Florida Museum of Natural History, first came across them.
He and colleagues used micro-CT technology to digitally scan images of the creatures without damaging the fossils. Stanley told Phys.org:2
"These fossils tell us a lot about the extraordinary, but previously unknown diversity of lizards in ancient tropical forests …
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."
The fossils revealed lizards that resemble modern-day geckos and chameleons as well as an ancient lizard that may represent an unknown species (you can see some of the CT scans in the video below). Some of the most intriguing findings included:
• A gecko with adhesive toe pads similar to modern-day geckos, which, Stanley told The Christian Science Monitor, suggests "even 100 million years ago geckos apparently already had evolved a well-diversified subset of tools for clinging onto surfaces." 3
• An ancient chameleon with the same projectile tongue found in modern-day chameleons, as evidenced by a long hyoid bone (a bone in the throat used to shoot out the tongue).
• The ancient chameleon-like specimen did not have the same modern body shape and fused toes meant for gripping seen in modern chameleons. Stanley told The Christian Science Monitor:4
"It's this interesting sort of halfway stop between a modern chameleon and the sister group to chameleons, which are the dragon lizards."
How Does Resin Preserve Animals for Millions of Years?
While there are many examples of insects and other small creatures preserved in amber, most samples contain only a part of the specimen, such as a foot. The lizard fossils were especially unique in that they contained many whole specimens, including claws, teeth, toepads and even colored scales.
Resin represents a perfect combination for fossilization, as it contains natural preservatives that enter tissues and sugars that draw moisture out. Tissues are therefore easily preserved within the resin and then hardened as amber forms around them.5
With such effective preservation, might it be possible to extract ancient DNA and recreate ancient species, as was done with dinosaurs in the film Jurassic Park?
Researchers from The University of Manchester, U.K., conducted an experiment to find out. They used an advanced type of DNA sequencing to attempt to extract DNA from ancient bees in copal, which is a resin precursor of amber.6
The samples were comparatively young at an estimated 60 to 10,600 years old, but the researchers were unable to detect any ancient DNA and concluded such DNA extraction was unlikely. They wrote in PLOS ONE:7
"We were therefore unable to obtain any convincing evidence for the preservation of ancient DNA in either of the two copal inclusions that we studied, and conclude that DNA is not preserved in this type of material.
… Our results raise further doubts about claims of DNA extraction from fossil insects in amber, many millions of years older than copal."
6 Other Amazing Amber Fossil Finds
Many other intriguing discoveries have been made courtesy of amber's fossilization potential. Among them:8
- 99 million-year-old ants, which allowed researchers at the American Museum of Natural History to describe 11 new species
- An approximately 20 million-year-old male scorpion, discovered by Mexican farmer in a dirt pit dug by hand; the rare fossil included the entire scorpion and represents a new species9
- A 40 million-year-old tentacle from a carnivorous plant, which resembles the modern Roridulacea plant family, which contain insect-trapping sticky hairs
- An ancient scale insect fossilized in Burmese amber with more than 60 eggs on her back, showing the earliest known evidence of insects caring for their young
- Dinosaur feathers with the colors — gray, red, white and brown — still preserved were discovered in amber from Canada
- A group of 17 Anolis lizards from the Caribbean were preserved in amber and date back up to 20 million years; researchers found many similarities to modern-day lizards in the specimens
The fossil finds are fascinating to learn about, but they also represent an important lesson about protecting the planet's biodiversity.
In the case of tropical forests, for instance, there are species living there that are very similar to those that lived millions of years ago, speaking to the stability of the forest regions and also the extreme losses that could be faced if such habitat is increasingly destroyed. Stanley told Phys.org:10
"These exquisitely preserved examples of past diversity show us why we should be protecting these areas where their modern relatives live today … 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."