Ancient protein dating back 80 million years to the Cretaceous geologic period has been preserved in bone fragments and soft tissues of a hadrosaur, or duck-billed dinosaur, according to a study in the May 1 issue of Science. Led by scientists at Beth Israel Deaconess Medical Center (BIDMC) and North Carolina State University (NCSU), the new findings support earlier results from analyses suggesting that collagen protein survived in the bones of a well preserved Tyrannosaurus rex, and offer robust new evidence supporting previous conclusions that birds and dinosaurs are evolutionarily related.
In April 2007 John Asara, PhD, Director of the Mass Spectrometry Core at BIDMC, together with NCSU paleontologist Mary Schweitzer, PhD, published two papers in Science describing their discovery that collagen extracted from bone fragments of a 68-million-year-old T. rex closely matched the amino acid sequences of modern day chickens. Not surprisingly, the widely publicized findings created a great deal of controversy.
"With this new paper, we hoped to show that our T. rex discovery was not a unique occurrence," notes Asara, who is also an Instructor in Pathology at Harvard Medical School. "This is the second dinosaur species we've examined and helps verify that our first discovery was not just a one-hit wonder. Our current study was the collaborative effort of a number of independent laboratories, whose findings collectively add up to a robust conclusion."
At the heart of the controversy is the idea that ancient protein can exist at all. When an animal dies, protein immediately begins to degrade and, in the case of fossils, is slowly replaced by mineral, a substitution process assumed to be complete by 1 million years. But with this latest evidence, it appears that some proteins do indeed have real staying power.
"We wound up identifying nearly double the number of amino acids we recovered in the T. rex study," says Asara. "The sequences displayed high spectral quality and the interpretations were of high confidence."
The two scientists had decided to collaborate again after Schweitzer and paleontologist Jack Horner of Montana State University's Museum of the Rockies recovered the 80-million-year-old Brachylophosaurus canadensis femur bone in the summer of 2007 and observed that it appeared to be even better preserved than the original T. rex fossil.
Schweitzer's initial laboratory analyses confirmed this observation: After being subjected to demineralization, the B. canadensis bone fragments showed marked preservation of original tissues and molecules, with microstructures resembling soft, transparent vessels, cells and fibrous matrix – even though the fossil was much older than the T. rex sample.
"Deep burial in sandstone seems to favor exceptional preservation," notes Schweitzer, explaining that this fossil was found under approximately seven meters of sandstone in the Judith River Formation, in parts of what is now Eastern Montana.
Chemical extractions of bone and vessel were subsequently sent to the laboratories of BIDMC scientists Lewis Cantley, PhD, and Raghu Kalluri, PhD, where immunoblots and immunochemistry analyses were conducted to determine the presence of collagen protein in the samples.
"Having been a part of the T. rex study, I was curious to be part of this investigation as well," explains Cantley, Chief of the Division of Signal Transduction at BIDMC. "In view of the skepticism about the original findings, it was important to demonstrate that our findings in T. rex could be verified in another dinosaur and in other laboratories."
The results confirmed the existence of protein. "Because I am a collagen biochemist, our lab was contacted to perform an independent analysis of this new bone find," explains Kalluri, who is Chief of the Division of Matrix Biology at BIDMC. "We isolated the proteins – collagen, laminin and elastin – from the bone, and also extracted bone cells and blood vessels from this sample. Our findings demonstrated that it did contain basement membrane matrix."
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