Walking in the garden, we will be surrounded by the colorful colors of nature. There are green leaves, grass, and beautiful flowers everywhere. Among the flowers, there are colorful butterflies dancing; on the leaves, there will be green or blue scarabs and jerky beetles. If you are lucky, you can also enjoy the light-yellow fireflies dancing in the midsummer evening. In fact, these types of colors represent the three types of colors that people observe in nature.
The green of leaves and the colorfulness of flowers are typical pigment colors. The production of such colors requires the participation of pigment molecules, so they are also called chemical colors; It is formed by the optical interaction between the ultra-microstructure on the surface of the organism or the superficial outer skin and natural light, and it is also the purest and most intense color in nature. In addition, there is a relatively special form of color production in nature-bioluminescence, which is formed by chemical substances synthesized by cells. Under the action of luminescent enzymes, chemical energy is converted into light energy. Fireflies and some deep-sea fishes , and some glowing mushrooms, all fall into this category.
Today’s nature is full of colors, but what did the colors of ancient creatures look like? Can Paleontological Fossils Preserve Their Original Colors? Based on the preservation of the skin and feathers of ancient creatures by fossils, paleontologists began to try to start from the ultrastructure of skin and feathers, looking for pigment cells or chromophores involved in color formation, so as to reconstruct the original colors of ancient animals.
The color of ancient animals no longer depends on imagination
In the autumn of 2006, when a Danish boy named Jakob Vinther was doing research on the specific burial of cuttlefish and their ink sacs, he observed that the cuttlefish-like graphite sacs were preserved in the form of solid organic clumps, and these clumps were composed of The composition of melanin in the ink is the same as that of modern cuttlefish. From this observation, he boldly speculated that the chemical properties of fossil melanin seem to be very stable and can be stored stably for hundreds of millions of years. Then he thought, since melanin can be preserved in cuttlefish, can it also be preserved in other ancient organisms? If so, it might be possible to restore the colors of feathered dinosaurs.
After having an idea, Jakob borrowed a feathered bird fossil from the Danish Museum for research, and made an amazing discovery with the help of a scanning electron microscope—a large number of regularly arranged, sausage-shaped melanosomes were found on the fossil bird feathers. Not long after, he and his supervisor studied in detail the early Cretaceous bird feather fossils from Brazil. Using a scanning electron microscope to observe that the feather had black and white horizontal stripes, it was found that there were a large number of sausage-like structures in the black spots, but there were no white spots. , proving that these sausage-like structures should be melanosomes containing eumelanin. Jakob then studied bird feathers found in the Messer oil shale in Germany and found structural colors on such feathers. After a series of research results were published, paleontologists are eager to try to find melanosomes on the feathers of birds or furry dinosaurs in specific buried biota, and then reconstruct the original colors of ancient birds and dinosaurs.
In January 2010, Chinese and British scientists led by Zhou Zhonghe, academician of the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, and Mike Benton, fellow of the University of Bristol, reported in the journal Nature that several species of dinosaur feathers were preserved. There are melanosomes. It is found that the tail of Sinosauropteryx can be divided into dark and light-colored zones. Through the observation of the size, shape and arrangement of the melanosomes in the feather traces, and the comparison with the melanosomes in the feathers of modern birds According to the comparative study, it is speculated that the color represented by the feather melanosomes in life is chestnut or reddish brown.
In March 2010, a Chinese and American team led by Jakob reported in Science that they had completely restored the whole body of a small theropod dinosaur, Anchiornis hermitii, using almost the same principles and methods. feather color. Once the results were published, it caused a huge sensation in the academic circles, setting off an upsurge of research on the reconstruction of melanosomes and colors of ancient animals, and the colors of some ancient animals such as dinosaurs, ichthyosaurs, and snakes were quickly reconstructed.
Recently, Academician Zhou Zhonghe and Pan Yanhong, a researcher at the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, used a variety of chemical and molecular analysis methods, including immunoelectron microscopy and ultra-high resolution elemental energy spectrum analysis, to prove that the 130 million-year-old bird fossil The preservation of β-keratin in feathers also verifies that the nano-scale microstructure in feather fossils is wrapped by β-keratin, which is indeed the melanosome of feathers. Since then, the color reconstruction of ancient animals is no longer an artist’s imagination, but an inference with certain scientific basis.
Reconstruction of oldest insect structural color
Ancient vertebrates, including dinosaurs, have always been the stars of paleontological research. Paleontologists, led by a wave of reconstructions of the colors of dinosaurs and ancient birds, have since turned to some of the most biodiverse insects on Earth.
Maria McNamara, a scholar in the same laboratory as Jakob, reported in late 2011 a 47-million-year-old moth found in the Messer oil shale in Germany. By observing the ultrastructure of the small scales on their wings, they found that these scales contain a multi-layer reflective film structure. When light is reflected at different levels of this structure at the same angle, it can produce a single visible light and It is speculated that the color on the wings can help moths hide from possible predators (such as bats) and avoid being eaten. The study demonstrates an “arms race” between predators and prey going back 47 million years.
A year later, Maria’s team reported another batch of beetle fossils from 47 million to 15 million years ago. Through scanning electron microscope observations, it was found that this original metallic luster was due to the multi-layered skin located on the insect’s outer skin. Nanostructures on the reflective film, which form a typical structural color. The existence of this structure is the reason why metallic luster colors can be preserved for a long time in geological history. However, their simulations found that the beetle fossils were slightly redder (at a longer wavelength) than they should have been. So the fossilized beetles didn’t quite preserve their original colors.
In April 2018, the team of Wang Bo, a researcher at the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, reported Jurassic moth specimens from the United Kingdom, Germany, Kazakhstan and China, as well as Mesoptera (the distant ancestor of butterflies and moths) in Burmese amber from the Cretaceous Period. insect. Using a variety of microscopic imaging techniques, three-dimensional optical modeling and other technical methods, the microstructure and possible structural color of the scales in this batch of fossils were analyzed. The study found that the Jurassic moth scales have evolved a fishbone-like nano-optical structure, forming a diffraction grating, similar to the living small winged moth. Structural colors of fossil caddis moths were calculated by combining topographical data of the scales and model simulations, which can produce silver or golden yellow. The discovery represents the oldest known structural coloration of insects and advances the record by at least 130 million years.
The study found that the Jurassic moth scales have evolved a fishbone-like nano-optical structure, forming a diffraction grating, similar to the living small winged moth. Structural colors of fossil caddis moths were calculated by combining topographical data of the scales and model simulations, which can produce silver or golden yellow. The discovery represents the oldest known structural coloration of insects and advances the record by at least 130 million years.
The “time capsule” has a big mystery
Most of the insects preserved in the form of imprinted fossils cannot preserve the original color of the insects. Amber, also known as “time capsule”, vividly preserves small life hundreds of millions of years ago in a special way. However, most insect fossils in amber do not preserve obvious structural colors, and insects with metallic colors are rarely reported, mainly found in Eocene Baltic amber, Miocene Mexican amber and Colombian copal. At that time, scholars only paid attention to the morphology and classification of insects, and did not study the preservation, formation mechanism and ecological significance of colors in depth.
In recent years, the author’s research team has systematically studied a large number of metallic-colored insects in Burmese amber from the Cretaceous period about 100 million years ago, and found that pure and intense colors can be directly preserved on the surface of various insects. The research team used ultra-thin sections of amber, scanning electron microscopy, and transmission electron microscopy to prove that the blue-green color of the green bee’s chest is formed by multiple layers of repeated nanoscale structures, which is a typical and common structural color. Type, that is, the multi-layer reflective film structure (it can be simply understood as the superposition of multiple layers of soap bubbles).
In addition, through the optical theoretical model, it is proved that its reflection wavelength is close to the wavelength of the insect color observed by the naked eye, indicating that the color displayed by the amber insect body may be the original color, and it proves that the ultra-fine and nano-scale optical structure can be used in geological history. The stable preservation in Mesozoic fossils negates the previous view that insect metallic colors cannot be preserved in Mesozoic fossils.
Our team focused on the study of 35 exquisitely preserved Cretaceous insect fossils with metallic luster, including Hymenoptera, Coleoptera and Diptera, a total of 3 orders, most of which belonged to the Hymenoptera Chrysalis family, and a few Belongs to Coleoptera Paedopteridae, Ceratophyllidae and Paedopteridae, and Diptera Soldier Flyidae. All or part of the body structure of most insect species is metallic green, blue, turquoise, yellow-green, or bluish-purple. Through taxonomic and comparative studies, it is found that the living genera corresponding to these fossil insects also have similar metallic luster colors, which directly proves that the bright structural colors of Mesozoic insects can be preserved. Moreover, through the ultramicro analysis of one of the specimens of the fossil green bee, it is confirmed that the multilayer reflective film is the direct cause of the structural color.
At the same time, we also found an interesting phenomenon: the structural color that seemed to be preserved forever in amber 100 million years ago did not remain unchanged. If any small part of the structure of amber insects is damaged during the previous processing (such as cutting, grinding and polishing, etc.), and it is exposed to air or moisture, its color will change in a short period of time (days or weeks). into pure silver, but the metallic luster remains, and this change is irreversible. The discovery of this phenomenon explains the formation of silver insects in Burmese amber and even other ambers, and has reference significance for the correct description of the morphological characteristics of amber insects.
What is the use of structural colors in amber insects? It is generally believed that the more common green color is likely to be the camouflage color of insects in dense forest environments, which helps insects hide themselves and avoid predators. In addition, structural color can also participate in the thermal regulation of insects. Therefore, the structural colors of different hues found in different species of insects partly indicate that complex ecological relationships already existed in mid-Cretaceous forests.
The reconstruction of the feather color of ancient vertebrates represented by dinosaurs is a hot spot in paleontology research, but the research on the color of ancient invertebrates is not deep and extensive enough. As a very special form of fossil preservation, amber provides a unique window into the original structural colors of ancient insects. With the discovery of more beautifully preserved fossils and the application of new technologies and methods in the study of amber fossils, it is believed that more mysteries of ancient animal colors will be revealed.