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Fossil Pigments Reveal the True Colors of Dinosaurs
Long thought impossible, preservation of fossil pigments is allowing scientists to reconstruct extinct organisms with unprecedented accuracy—a feat that is yielding surprising insights into the lives they led
By Jakob Vinther on March 1, 2017
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When we applied our method to the melanosomes of Anchiornis, the results were striking. Our statistical predictions indicated that the feathers that covered much of the creature’s body were mostly gray. The long feathers on the animal’s arms and legs, in contrast, were unpigmented by melanosomes and thus white, except for the melanosome-laden tips, which we predicted were black. (Modern birds often have black-tipped wing feathers. The melanin, in addition to coloring the feathers, also fortifies them against battering winds. Perhaps Anchiornis benefited from this strengthening property of melanin, too.) Most surprising, the feathers on the crown of the head contained impressions of round melanosomes—the “meatballs”—that would have given Anchiornis a ruddy crest. All told, this combination of colors made for a spectacularly flamboyant creature.
At around the same time we published our Anchiornis study, Fucheng Zhang, then at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, Michael J. Benton of the University of Bristol and their colleagues reported that they had found fossil melanosomes in a range of birds and dinosaurs recovered from 130-million-year-old rocks in China. The pattern of meatball melanosomes in one fuzz-covered dinosaur, Sinosauropteryx, implied that it had sported a reddish coat and a tiger-striped tail, making it the first known ginger dinosaur.
Since those early days our feather data set has grown to comprise hundreds of samples, including ones that allow us to accurately predict iridescence, the metallic sheen seen in the plumage of hummingbirds and peacocks, among other birds. Melanosomes responsible for this effect tend to be longer than typical ones, and they may even be hollow or flattened. The iridescence arises from the packing of the melanosomes within the feather. Certain configurations refract light in ways that create different colors, depending on the angle at which the animal is viewed or illuminated.
Amazingly, in 2009 we found evidence of iridescence in a 49-million-year-old fossil feather from Messel, Germany. The fossil, kept at the Senckenberg Museum in Frankfurt, preserves the original arrangement of melanosomes that generated the iridescence. They were packed into a dense, smooth layer found in the finest branches of the feather fossil, the barbules. There the melanosomes occurred strictly on the farthest edge of the feather and on the top surface, the only part that was not obscured by other, overlapping feathers. We deduced that the tips were iridescent because that arrangement of melanosomes is known to produce what is called thin-film interference, the kind that occurs when gasoline floats on water and creates a vivid rainbow of colors.
It was not long before we discovered evidence of iridescence in an actual dinosaur—a crow-size creature from China with wings on all four limbs. Dubbed Microraptor, it was a primitive cousin to Jurassic Park’s Velociraptor. The movie depicted Velociraptor with scaly skin, but scientists now know that both these dinosaurs were, in fact, covered in feathers. In Microraptor, the preserved feathers contain long, sausage-shaped melanosomes arranged to bend light in eye-catching ways. Its plumage thus would have been black, with the same shiny sheen as a crow’s. Microraptor is not the only extinct creature now known to have had that rainbow shimmer. Jennifer Peteya of Oberlin College and Ghent’s Shawkey have described shimmering iridescence in an enantiornithine bird, called Bohaiornis, and a Jurassic theropod with a big, fan-shaped tail, named Caihong.
More Than Skin Deep
Beyond allowing paleontologists and artists to reconstruct extinct organisms more accurately, fossil pigments are revealing previously unknown facets of the daily lives of both dinosaurs and other long-gone creatures. For instance, experts had presumed that Microraptor was nocturnal, based on the large size of its eye sockets. But our discovery that it possessed iridescent plumage suggests otherwise because in modern birds such coloration is typically found in species that are active in the daytime. The bold coloring of Anchiornis, for its part, probably helped to attract mates or served as some other kind of display, as occurs in flashily dressed modern birds. Thus, color patterns may provide a way to test behavioral hypotheses about a species using a different line of evidence than usual.
Fossil pigments in one species can also illuminate aspects of the other species with which it interacted. Among insects, most color patterns evolved not to help the creatures attract mates but rather as a tactic to avoid getting eaten. Their pigments can thus provide clues to their predators. Fossils of insects called lacewings offer a fascinating example. Between 170 million and 150 million years ago certain distinctive color patterns made their evolutionary debut in insects. Perhaps the most dramatic pattern to emerge during this time was the eyespot, a marking that resembles the eye of a different kind of animal and serves to startle predators approaching their prey at speed from a distance. Lacewings are among the first creatures known to have had eyespots. What kind of predator were they defending themselves against? Most color patterns of modern insects have evolved as a defense against birds, which are their main predators nowadays. But the lacewings’ eyespots predate the origin of birds as we know them. Their predators were instead most likely a small group of dinosaurs called the paravians, which are known to have lived at the same time as these lacewings and are thought to have given rise to birds. Although the fossil record of paravians themselves has not allowed us to unequivocally pinpoint when flight evolved in this group, the appearance of these eyespots in the lacewings hints that some paravian dinosaurs had taken wing by this point and were exerting birdlike predation pressure on the insects.
Other fossil melanosome discoveries have enabled my collaborators and me to reverse engineer the environment in which extinct organisms lived. Our first foray into this realm of investigation began with a particularly splendid fossil of a small, plant-eating dinosaur called Psittacosaurus, a relative of Triceratops. These dinosaurs’ skeletons are quite common in northeastern China and are often complete. This specimen stood out even in that good company, however. A thin film drapes its body—the remains of the skin, including delicate scales. And its tail displays long, filamentous bristles that may be precursors to feathers. Previous discoveries of dinosaur feathers have all come from the mostly carnivorous theropod group of dinosaurs. The bristles on Psittacosaurus, a distantly related member of the plant-eating ceratopsian group, hint that plumage might have been far more widespread among the dinosaurs than previously thought.
When I first encountered the specimen in 2009, a year after we had announced the discovery of melanosomes in fossil birds, I saw right away that it preserved evidence of beautiful color patterns all over the body. The patterns were subtle, with fine veining, dots and stripes. And I could see that the animal had a dark back that gave way to a pale belly. That kind of dark-to-light color gradient from back to belly counteracts the light-to-dark gradient created by illumination from the sun. This pattern, known as countershading, is common among modern animals ranging from dolphins to deer, helping both predators and prey blend in with their surroundings and thereby elude detection.
I eventually showed the Psittacosaurus pattern to Innes Cuthill, who is part of a group that studies camouflage at the University of Bristol. It was then that we realized we had the opportunity not only to study countershading in a dinosaur but also to deduce from the fossil alone what kind of environment the creature lived in. To reconstruct an animal’s habitat, scientists usually gather clues from fossils of other animals and plants found nearby. This kind of approach is problematic, however, because oftentimes the site where a fossil is discovered is not where the organism lived. The Chinese psittacosaur, for example, was recovered from sediments of an ancient lake. The creature was clearly not aquatic, so its remains must have been transported to the lake from the surrounding terrestrial environment, perhaps by moving water. Our study might be able to provide clues about that setting—specifically, the light conditions under which this dinosaur evolved its camouflage.
Cuthill and his collaborators had recently studied countershading in modern ungulates, the group that includes horses, antelope, camels, pigs and rhinoceroses. Although countershading by definition involves darker coloration on the back and lighter coloration on the underside (except in some animals, such as caterpillars, that live their lives upside down), the intensity of those shades and the nature of the transition from dark to pale differ from species to species. Cuthill’s team wanted to investigate how well that variation correlates to variation in the lighting conditions found in different environments. Because sunlight varies depending on the latitude at which an animal lives, as well as the density of vegetation in its habitat, the researchers had theorized that ungulate countershading, too, should differ according to latitude and habitat. Their findings bore out that notion. Broadly speaking, if an animal lives in open habitats, the direct sunlight will create a shadow high on the body, with a very sharp transition to the illuminated areas. These animals usually exhibit countershading that matches this pattern, with dark backs that almost immediately give way to pale bellies and little intermediate coloration in between. Pronghorn antelope offer a great example of this kind of countershading. In closed habitats, in contrast, the diffuse light that filters down through the vegetation scatters in all angles, producing a shadow that hangs farther down the body and transitions to the illuminated area gradually. White- and black-tailed deer, common in North American forestlands, exhibit this pattern.
We knew from our visual inspection of the Psittacosaurus fossil that it had countershading of some sort. We therefore carefully projected the pigment pattern onto an accurate, life-size model of the dinosaur, which we accomplished by enlisting the help of British paleoartist Bob Nicholls. Through this work we determined that the transition from dark to light occurred low on the belly and tail in Psittacosaurus.
To test the function of the dinosaur’s color pattern, we painted a second copy of the full-scale model gray. Next we photographed this model in a range of daylight conditions, from gloriously sunny to oppressively cloudy, as well as in open land and underneath conifer trees to capture the shadows cast on it. Next we inverted the dark and light shades in the photographs, effectively creating the ideal countershading patterns for concealing the animal in each of the lighting conditions. By comparing our reconstruction of the actual countershading pattern of the Psittacosaurus with the idealized countershading patterns, we determined that the animal’s coloring would have best camouflaged it in a habitat with diffuse light, such as that seen in a canopy forest.
Our work on Psittacosaurus didn’t end there. In 2021 we reconstructed its cloaca—the multipurpose orifice for defecation and breeding—in great detail. We could show that while the rest of Psittacosaurus‘s body was camouflaged, the flaring lips defining the cloacal opening were heavily pigmented and must have been used for signaling of some sort, most likely for mating.
Subsequent studies on countershading found that the tiger-striped Sinosauropteryx was adapted to live in open environments with bright sunshine from above and that it carried a striped tail and a bandit mask of pigmented feathers over its eyes. Psittacosaurus and Sinosauropteryx are found in the same fossil beds, but their countershading tells us that they came from different environments.
A nearly six-meter-long ankylosaur, Borealopelta, was found in the approximately 112-million-year-old marine oil sand beds in northern Alberta, Canada. It was colored with reddish-brown pheomelanin and was countershaded. Living land animals of such size are not countershaded, because there are no predators big enough to threaten them. In other words, for such a big creature to maintain its countershading from generation to generation, the Cretaceous predators must have been vicious enough to have threatened it. Perhaps that doesn’t come as a big surprise considering the spine-chilling Herculean dimensions of the theropod predators back then. But now we have rock-solid proof in fossil color pattern of their gruesomeness.
A Vivid Future
Scientists still have much to learn about paleocolor. Our ability to see broad categories of color in fossils—those that stem from the shape and arrangement of melanosomes—is already a massive leap forward from what we knew about ancient hues 15 years ago. But there are other pigments to look for in fossils, including carotenoids, which produce bright reds and yellows, and porphyrins, which produce such hues as green, red and blue. These pigments have turned up in the fossil record on occasion. Researchers have identified carotenoid pigments derived from fossil bacteria dating back several billion years; porphyrins are preserved in a blood-engorged mosquito from 46 million years ago and in the eggs of a 66-million-year-old dinosaur known as an oviraptorosaur. Pigments not known from modern organisms have come to light, too, including some from fossil sea lilies and algae dating to between 300 million and 150 million years ago.
We will probably encounter limitations to the detail with which we can reconstruct paleocolors; over millions of years some information is bound to be lost forever. In addition, because exceptional fossils with organic preservation are rare and precious, we must restrict destructive chemical sampling of them. As techniques advance, however, the new discoveries they afford will undoubtedly change our understanding of the past faster than ever before. Each one will bring us that much closer to seeing dinosaurs and other prehistoric creatures as they really were, in full Technicolor glory.
This article was originally published with the title “The True Colors of Dinosaurs” in Scientific American 316, 3, 50-57 (March 2017)
MORE TO EXPLORE
The Colour of Fossil Feathers. Jakob Vinther et al. in Biology Letters, Vol. 4, No. 5, pages 522-525; October 23, 2008.
3D Camouflage in an Ornithischian Dinosaur. Jakob Vinther et al. in Current Biology, Vol. 26, No. 18, pages 2456-2462; September 26, 2016.
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ABOUT THE AUTHOR(S)
Jakob Vinther thought he was going to become a botanist until he found his first fossils at age 11 while attending summer camp in his home country of Denmark. Today he is an associate professor of macroevolution at the University of Bristol in England. His research focuses on pigments and other molecules preserved in the fossil record. Credit: Nick Higgins
