Scientists have discovered fragments of protein inside a 195-million-year-old dinosaur bone, by far the oldest such traces of soft tissue ever detected.
The find – a technical tour de force that did not require destroying the bone to analyze its contents – is another indication of the potential for new laboratory methods to reveal details about long-extinct species that were previously thought inaccessible.
"In future, this is information that could be harnessed for evolutionary studies, for connecting species that are related to one another and for understanding their biology," said Robert Reisz, a paleontologist at the University of Toronto and the senior member of the team behind the find.
The bone that yielded the discovery was the rib of a Lufengosaurus, a long-necked plant-eating dinosaur that roamed what is now southwestern China in the early part of the Jurassic period. The results were published Tuesday in the journal Nature.
This image shows a thin section of the Lufengosaurus's rib, cut along the length to reveal a tiny vascular canal. Inside the canal are dark particles made of the mineral hematite, probably derived from the living dinosaur's iron-rich blood cells. (Courtesy of Robert Reisz)
Dr. Reisz and his colleagues from Taiwan and Changchun, China, cut open the bone to reveal tiny vascular channels that once held blood vessels. By probing one of the channels with infrared light and analyzing how different wavelengths are absorbed by the sample, researchers were able to tease out the chemical signature of type I collagen, a protein that is commonly found in the structural tissues of animals, including in the walls of blood vessels.
In previous studies, scientists have used collagen found in more recent fossils to identify and distinguish between different kinds of ancient mammals. In this case, the amount of collagen found in the dinosaur rib was far too little to yield such specifics.
"We can identify that there's collagen there but there isn't enough for us to characterize it," Dr. Reisz said. The significance of the find is that the team was able to find any sign at all of organic material in such an old specimen. Until now, the oldest-known dinosaur collagen is from an 80-million-year-old fossil investigated by researchers at North Carolina State University.
The Taiwanese researchers Dr. Reisz worked with developed a method that does not require destroying the part of the bone that is analyzed and permits detection of very small amounts of collagen. It lays the groundwork for microscopic explorations of fossils that may be able to extract valuable insights from proteins locked in tiny, protected pockets deep within bones.
"Evidence has been accumulating that fossil bone is much more than a piece of rock," said Martin Sander, a paleontologist at the University of Bonn, Germany, who was not involved in the find. "Right now we know that a lot more organic material remains preserved in bone than what was believed possible, and the ultimate goal would be to use these preserved molecules to detect [evolutionary] relationships in dinosaurs."
Dr. Sander added that prospects for discovering preserved dinosaur DNA, a far more fragile molecule than collagen, "remains unlikely."
One of the intriguing details in the finding is that the vascular channel also contained grains of the iron-rich mineral hematite. Dr. Reisz said that he suspect the iron in the mineral many have originally come from the dinosaur's blood. The hematite may have anti-bacterial properties that helped to preserve the collagen over geologic time.
Dr, Reisz is set to travel to northern China next month to look at another group of fossils, some of which he said could yield additional traces of organics.
"What we want to do is to push the boundary further and see whether we can get that collagen signal in even older material," he said.