Incredible specimens preserved in amber for 99 million years have revealed the amazing technicolor of insects that were alive when dinosaurs were still roaming the Earth. A new study published in Proceedings of the Royal Society B demonstrates in stunning technicolor what some insects from the mid-Cretaceous looked like, shedding new light on the behavior and ecology of insects in the deep geological past.
It’s unusual for fine structural detail to be preserved in the fossil record, meaning the coloration of most prehistoric animals involves extensive analysis combined with some artistic license. However, a treasure trove of 35 amber specimens lifted from a mine in northern Myanmar were found to have preserved the delicate morphology of insect species that coexisted with the dinosaurs.
"The amber is mid-Cretaceous, approximately 99 million years old, dating back to the golden age of dinosaurs,” said Dr CAI Chenyang, associate professor at Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences (NIGPAS), in a statement. “It is essentially resin produced by ancient coniferous trees that grew in a tropical rainforest environment. Animals and plants trapped in the thick resin got preserved, some with life-like fidelity.”
The incredible collection of resin easter eggs contained a diverse range of insect life, from cuckoo wasps still sporting metallic blue, green, and yellow that CAI says are similar in color to today's cuckoo wasps, to a beetle species steeped in blue and purple. "We have seen thousands of amber fossils but the preservation of color in these specimens is extraordinary," said co-author Professor Huang Diying from NIGPAS.
Colour preserved in this way is called structural color and caused by tiny structures on the surface of the insect's exoskeleton scattering wavelengths of light to produce intense, iridescent colors. Structural color is the same phenomenon that makes the feathers of Cassowary birds so shiny.
The researchers wanted to understand why the color in these specimens was so well preserved when this isn’t the case for other amber specimens. To find out, they cut through their colorful fossils with diamond knife blades (essentially a knife with a diamond tip, very sharp and very cool) and compared the structures to those in dull, brown-black specimens using electron microscopy.
They found that the insects’ nanostructures were unaltered, meaning they retained their color whereas the dull samples were badly damaged. This indicates that the perfectly preserved insects were as colorful in the Cretaceous as they appear today.
Knowing this, scientists can use color cues from the insects to inform how they lived. For example, extant colorful cuckoo wasps use structural coloration to camouflage so it’s possible these ancient specimens shared this behavior. Alternatively, the insect’s surface structure could play a role in thermoregulation, so further research is needed to draw probable conclusions, but with such perfectly preserved specimens as these scientists can begin to paint a much clearer, more colorful picture of entomology in the Cretaceous.
What kind of information can we learn about the lives of ancient insects from their color? Extant cuckoo wasps are, as their name suggests, parasites that lay their eggs into the nests of unrelated bees and wasps. Structural coloration has been shown to serve as camouflage in insects, and so it is probable that the color of Cretaceous cuckoo wasps represented an adaptation to avoid detection. "At the moment we also cannot rule out the possibility that the colors played other roles besides camouflage, such as thermoregulation," said Dr CAI.