Color Explosion Led to Fabulous Dinos 150 M Years Ago
Michael A. Digiorgio
Reconstruction of the small feathered non-avian dinosaur Anchiornis.
Sept. 15, 2011 --
A stunning array of prehistoric feathers, including dinosaur protofeathers, has been discovered in Late Cretaceous amber from Canada. The 78 to 79-million-year-old amber preserved the feathers in vivid detail, including some of their diverse colors. The collection, published in this week's Science, is among the first to reveal all major evolutionary stages of feather development in non-avian dinosaurs and birds. In this slide, an isolated barb from a vaned feather is visible trapped within a tangled mass of spider's web.
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"These specimens were most likely blown into the tacky resin, or were plucked from an animal as it brushed against resin on a tree trunk," lead author Ryan McKellar told Discovery News. "The fact that we have found some specimens trapped within spider webs in the amber would suggest that wind played an important role in bringing the feathers into contact with the resin," added McKellar, a postdoctoral fellow at the University of Alberta's Department of Earth and Atmospheric Sciences. The feather filaments shown here are similar to protofeathers that have been associated with some dinosaur skeletons.
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McKellar and his team made the discovery after screening over 4,000 amber samples from Grassy Lake, Alberta. The amber, collected by the Leuck family, is now housed at the Royal Tyrrell Museum. The researchers ruled out that the inclusions were mammal hairs, plant or fungal remains based on their structure. Some dinosaur fossils retain skin impressions, so the scientists could match dinosaur protofeathers (hair-like projections) to some of the objects within the amber. Here, a feather is visible near a plant bug. The high number of coils in the this feather suggests it could have come from a water-diving bird.
The translucent tree resin provides a window into feather evolution, from non-avian dinosaurs to birds. "Part of what makes this particular set of feathers interesting is that we find the very simple Stage I and II feathers alongside advanced feathers that are very similar to those of modern birds, Stages IV and V," McKellar said. The researchers aren't yet certain why feathers first evolved, but the density of the protofeathers suggests that they helped dinosaurs with regulating temperature. Dinosaurs such as Troodon or Deinonychus may have produced the feathers. The cork-screw shaped structures in this slide are the tightly coiled bases of feather barbules.
As feathers continued to change, they developed tufts, barbs, branching features, little hooks, and more. Some of the most advanced feathers in the collection are comparable to those of modern grebes. They appear to help diving, indicating that some of the prehistoric birds were divers. McKellar suspects the marine birds might have been Hesperornithiformes, a specialized flightless diving bird from the Dinosaur Era. This is a white belly feather of a modern grebe, showing coiled bases comparable to those seen in the Cretaceous specimen.
Some of the feathers appear transparent now, but would have been white in life. A range of colors for the feathers is evident, though, with grays, reds and various shades of brown preserved. This, and prior research, suggests that non-avian dinosaurs and prehistoric birds could be quite flashy. The pigment within this fossilized feather suggests it would have originally been medium- or dark-brown in color.
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In an accompanying "Perspectives" article in Science, Mark Norell points out that the dinosaur Sinosauropteryx is thought to have had a reddish banded tail, while Anchiornis likely possessed a striking black body, banded wings and a reddish head comb. Norell, chair and curator of the American Museum of Natural History's Division of Paleontology, told Discovery News that the newly discovered feathers are "very exciting." Here, a feather barb within Late Cretaceous Canadian amber shows some indication of original coloration.
Some dino aficionados have wondered if DNA could be extracted from the feathers. "Almost anything is possible," Norell said, quickly adding that most DNA-extraction studies have been conducted on much younger amber, dating to around 20-30 million years ago, and even those led to questionable results. "Maybe bits and pieces could be identified, but not the whole genome." Shown are 16 clumped feathers in Late Cretaceous amber.
People with amber objects, such as jewelry, also probably don't have prehistoric feather inclusions, since such items are extremely rare and dealers isolate the best pieces. Nevertheless, McKellar said, "There is some hope that you could have small feather fragments that have been overlooked." An unpigmented feather and a mite in Canadian Late Cretaceous amber.
Dinosaurs went from drab to colorful fab just before 150 million years ago, according to a study published in the latest issue of the journal Nature.
The "Wizard of Oz"-type moment in evolution appears to coincide with the emergence of feathers.
Researchers determined this after studying pigment-containing organelles known as melanosomes. These specialized structures within cells in living organisms contain melanin, which is the most common light-absorbing pigment found in animals.
"Black, brown and grey colors are melanin-based," co-author Julia Clarke told Discovery News. "In birds, melanin-based colors include a slightly larger range of reddish brown, brown, black, grey, black and many forms of iridescence."
Clarke is an associate professor at the University of Texas at Austin's Jackson School of Geosciences. She and her colleagues compared the melanosomes of 181 diverse living animals, including birds, mammals and reptiles, as well as 13 fossil specimens and all previously published data on this subject.
Before it was determined that diversity in the shape and size of melanosomes is associated with the evolution of melanin-based color in non-avian dinosaurs, birds and mammals. This diversity in dinos happened suddenly, just as small, meat-eating maniraptoran dinosaurs were evolving feathers, the study found.
"This shift is not seen close to the origin of dinosaur 'fuzz' or 'protofeathers,' but is only associated with feathers," Clarke said. "The shift seems abrupt and occurs before the origin of anything we would call avian flight."
While she and her team are not sure why dinosaurs experienced such a color explosion, Clarke said the dramatic change could have facilitated mate selection. Just as pretty, colorful birds today catch our eye, colorful exteriors would have probably grabbed the attention of non-flying dinosaurs and literal 'early birds' seeking sexual partners.
In these living specimens, color and the shape of the melanosomes are not linked in such a way that color can be reconstructed from melanosome shape alone. Melanosomes in Sinosauropteryx don't presently tell us if this animal was brown, blackish or grey. However, feathered dinosaurs are similar to birds, and scientists can estimate their color. Clarke et al.
Many of the genes involved in the melanin color system are also tied to basic functions such as food intake, reproductive behaviors, the "fight or flight" process and other things. So the researchers believe that the color explosion in certain dinosaurs might have been linked to larger changes in their anatomy and metabolism.
"What is most exciting is that tracking color could potentially offer insight into dinosaur physiology," Clarke said.
The research could, for example, help to reveal the precise bodily changes that took place just as non-avian dinosaurs were evolving into birds, and why those changes occurred in the first place.
Color for color's sake is also of interest, allowing us to better recreate and envision what long-extinct animals looked like. This has been a challenge for researchers studying rather drab-looking fossils.
"The presence of pigment must not be confused with color, as even with a specific pigment being recognized, there are/were many factors that contribute to an organism's entire color palette," paleontologist Phillip Manning of the University of Manchester told Discovery News.
He continued, "Color is a function of the interaction of light with the surface structure and chemistry of a substrate (whether this be carapace, keratin, feathers, skin, scales or hair). The chemistry can be in part from pigments, but also from substances eaten by an organism, such as the pink of flamingos from their shrimp diet."
"There has possibly been wonderful color throughout the evolution of life on Earth," he concluded, "but whether the species alive could see or perceive it, as we or other species alive do today...that is a tougher question."