Low Oxygen Dino Air Trapped in Amber
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.
Amber may not preserve dino DNA, as in Jurassic Park, but the fossilized tree sap did trap clues about the air the extinct beasts breathed. Amber analysis revealed that dinosaurs inhaled air with far less oxygen than the modern atmosphere holds.
Mineralogists recently examined the chemical composition of 538 samples of amber and tree resins dating from the current Quaternary period to as far back as the Triassic period, 220 million years ago, when dinos were first staking their claim on the planet. The Quaternary period is the present stage of the Earth’s development, which includes the Ice Ages and the whole of human history.
Nowadays in the Quaternary, humans fill their lungs with air containing approximately 21 percent oxygen. However, amber from the dinosaurs’ time holds chemical clues that the dinos breathed in only 10 to 15 percent oxygen air.
Previous studies in Nature and the Proceedings of the National Academy of Sciences suggested that high oxygen levels fueled the evolution of giant insects and other lifeforms. However, the new amber study’s results suggest oxygen levels didn’t super-charge dino’s ability to grow to tremendous sizes.
“We do not want to negate the influence of oxygen for the evolution of life in general with our study, but the gigantism of dinosaurs cannot be explained by those theories,” said Ralf Tappert of the University of Innsbruck and lead author of the amber study, published in the journal Geochimica et Cosmochimica Acta, in a press release.
Amber and non-fossilized tree resins trapped a record of changing oxygen levels because sap-oozing trees intake of carbon dioxide changed depending on oxygen concentration. When oxygen levels changed, the trees collected different amounts of a form of carbon, an isotope known as carbon-13.
During the dinosaur era, volcanic activity may have increased the amount of carbon dioxide in the air. This increased the greenhouse effect, which subsequently increased oxidative weathering, or the amount of oxygen bound to other chemicals during the weathering of rocks, according to the study.
IMAGE: Oligocene-era gecko trapped in amber. (PG Palmer, Wikimedia Commons)