Earlier DNA studies indicated anolis lizards began colonising the Caribbean about 40 million years ago, quickly diversifying into different niches such as the forest canopy, tree branches, main trucks, leaf litter on the forest floor, or grasslands.
As different groups began occupying different niches, their body shapes, leg length, and the little scales on their toe pads that help them climb like geckos, changed accordingly to suit each niche.
Using x-ray microcomputer tomography to produce three dimensional reconstructions of the fossils inside their amber cocoons, the researchers showed that the diversity of lizards that resulted 20 million years ago is the same seen today.
"Given we see the same range of morphological features this means the community of lizards has remained unchanged all this time," says Sherratt.
Sherratt says it is "very striking" that the lizards don't seem to have changed at all during this long period, during, over which all the main animal types evolved.
"Evidence of anolis lizards living unchanged in different niches for 20 million years, indicates these niches have been stable for that period of time," she says.
"That's quite surprising because these lizards have gone to other islands and over to the Florida mainland where they seem to evolve very rapidly. So it's not that they don't have the propensity to change, it's just that the structure of the environment has been stable enough that they haven't needed to change in 20 million years."
Available evidence suggests that ecological communities change rapidly over the short term, says Sherratt.
However, she says, the findings are among the first to look at long term stability of ecological communities, and show that niches and the communities they support can remain stable over millions of years.