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The 68-million-year-old T.rex femur that has yielded the oldest proteins ever recovered from a fossil. Credit: Science SYDNEY: Protein has been extracted from a 68-million-year-old Tyrannosaurus rex fossil. U.S. researchers behind the find argue that its sequence is the first direct evidence for a genetic link between dinosaurs and modern birds. The team recovered intact collagen, the major soft-tissue component of bone, in minute concentrations from the leg bones of that fossil – a feat that has never been achieved before. In addition, they teased protein sequences linking dinosaurs to modern birds from the ancient molecules. "Most people believe that birds evolved from dinosaurs, but that's based on the architecture of the bones," said John Asara, of Harvard Medical School in Boston, Massachusetts. This allows us to confirm "they really are related because their sequences are related," he said. Asara is lead author of one of two papers reporting the find in the U.S. journal Science today. Back in 2005, palaeontologist Mary Schweitzer at North Carolina State University, in Raleigh, reported that her team had found soft tissues – blood vessels, cells, and possibly proteins – still intact in the fossil, discovered in the sandstone of eastern Montana. This was a remarkable discovery as most soft tissues, protein and DNA dcayed rapidly after death. Theories of fossilisation had held that in most fossils, especially specimens as old as this, all organic components would long since have degraded. Schweitzer, lead author of the other study published in Science today, decided to examine the fossil further using powerful microscopes and antibody tests. "We looked for collagen because it's plentiful, it's durable, and it has been recovered from other fossil materials – although none as old as this," she said. Microscope images showed structures usually associated with collagen, and extracts from the fossil reacted in a similar way to collagen in tests. But the only way to make certain that the substance really was collagen was to decipher its genetic code. To that end, Asara and his colleagues at Harvard used mass spectrometry, a highly sensitive technique, to determine the chemical composition and genetic sequence of the fossil sample. His group first successfully tested the method on collagen from a modern ostrich and a fossilised mastodon - a relative of the modern elephant - that was up to 600,000 years old. They then anlysed fragments of the T.rex collagen and found that it has changed relatively little over millions of years - some sequences exactly matched modern-day frogs, newts and particularly chickens. "These are two very interesting papers," commented Merrill Rowley, of Monash University in Victoria, Australia, who has herself analysed collagen from more recent fossils. A common problem when working with ancient molecular samples, said Rowley, is that they are susceptible to contamination from animals like humans after being unearthed. However, she said, the T. rex sequences appear genuine because they contain several features that seem unlikely to have come from humans. Schweitzer agreed, saying that the sequence data from the T. rex more closely matches sequences from birds like chickens than any other animals whose genes have been sequenced. "The similarity to chicken is definitely what we would expect given the relationship between modern birds and dinosaurs," she said. "This data will help us learn more about dinosaurs' evolutionary relationships, about how preservation happens, and about how molecules degrade over time - which could also have some important medical implications for treating disease." More information: Analyses of Soft Tissue from Tyrannosaurus rex Suggest the Presence of Protein - Science 
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