A research team from the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences (NIGPAS) has revealed the secrets of the true coloration of insects from 99 million years ago.
As usual, the fine structural details necessary for color preservation are rarely preserved in the fossil record, which means that most fossil reconstructions are based on the imagination of the artists.
Colors offer many clues about the behavior and ecology of animals. They serve to keep organisms safe from predators, at the right temperature, or attractive to potential mates. So understanding the coloration of long-extinct animals can help us shed light on ecosystems in the deep geological past.
The study, published in ‘Proceedings of the Royal Society B’, offers a new perspective on the lives of insects that are often overlooked, which coexisted alongside dinosaurs in the Cretaceous rain forests.
Investigators gathered a treasure trove of 35 pieces of amber with exquisitely preserved insects from an amber mine in northern Myanmar.
“Amber is from the Middle Cretaceous, approximately 99 million years old, and dates back to the golden age of dinosaurs. It is essentially resin produced by ancient coniferous trees that grew up in a rainforest environment. Animals and plants trapped in the thick resin was preserved, some of them with real fidelity, “highlights Dr. Cai Chenyang, associate professor at the Nanjing Institute of Geology and Paleontology (NIGPAS) in China, who led the study.
The rare set of amber fossils includes Cuckoo wasps with metallic colors of teal, yellowish green, purple blue or green on the head, chest, abdomen and legs. In terms of color, they are almost the same as cuckoo wasps that live today, “says Dr. Cai.
The researchers also discovered samples of blue and purple beetles and a dark green metallic soldier fly. “We have seen thousands of fossils of amber, but the preservation of color in these specimens is extraordinary,” said Professor Huang Diying of NIGPAS, co-author of the study.
“The type of color preserved in amber fossils is called structural color. It is caused by the microscopic structure of the animal’s surface. The surface nanostructure scatters light of specific wavelengths and produces very intense colors. This mechanism is responsible of many of the colors we use. know about our daily life, “explains Professor Pan Yanhong, also from NIGPAS, a specialist in pale-color reconstruction.
To understand how and why color is preserved in some amber fossils but not others, and if the colors seen in the fossils are the same as the insects wore over 99 million years ago, the researchers used diamond blades for exoskeleton cutting of two of the colorful wasps of amber and a sample of normal opaque cuticle.
Using electron microscopy, they were able to demonstrate that the colorful amber fossils have a well-preserved exoskeleton nanostructure that scatters light. The unchanged nanostructure of colored insects suggested that the colors preserved in amber may be the same as those in the Cretaceous. In contrast, in fossils that do not retain color, the cuticular structures are badly damaged, which explains their brown-black appearance.
What kind of information can we learn about the life of ancient insects from their color? Existing cuckoo wasps are, as the name implies, parasites that lay their eggs in the nests of unrelated bees and wasps.
It has been shown that the structural coloration serves as camouflage in insects, so it is likely that the color of the cretaceous cuckoo wasps represented an adaptation to avoid detection. “At the moment, we cannot rule out the possibility of colors playing other roles besides camouflage, such as thermoregulation,” acknowledges Dr. Cai.