T. Rex soft tissue found in fossil likely contains DNA

T. Rex soft tissue found in fossil likely contains DNA



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Raleigh, N.C. — Two decades ago, paleontologist Mary Schweitzer made a shocking discovery: what appeared to be soft tissue, preserved in the fossilized bones of a Tyrannosaurus rex. The suspicion was a controversial one — it has long been thought that soft tissue disappears from a body in the years following death — but a recent analysis confirmed the presence of cells.

Schweitzer discovered in 1991 what she thought was a cluster of blood vessels in bone fragments from a 67-million-year-old T. rex. She made a similar discover in bone fragments from a T. rex discovered in Montana in 2000.

Part of the dinosaur had been encased in plaster to protect it during the 2001 move, but the resulting package was so heavy it had to be split in two. During the process, the dinosaur's leg was broken, leaving Schweitzer with bone fragments perfect for her research.

Upon examining the dinosaur, nicknamed "Bob" after Bob Harmon, the man who discovered it, Schweitzer found the dinosaur was actually a female, and had been pregnant at the time of its death.

T.rex (B), B. canadensis (E) and ostrich osteocytes (H) showing positive response to propidium iodide, a DNA intercalating dye.
T.rex (B), B. canadensis (E) and ostrich osteocytes (H) showing positive response to propidium iodide, a DNA intercalating dye. (Photo: North Carolina State University)

Schweitzer told the Smithsonian she had found bone fragments on the inside surface of the dinosaur's femur, which would have functioned in a manner similar to how birds create eggshells during breeding season.

Schweitzer determined her hypothesis was correct upon comparing the bone to those of emus and ostriches, and published a paper on the find in the June 2005 issue of the journal Science.

Further testing led to the discovery of what was once thought impossible: a fragment of soft tissue left behind when the fossilized bone around it was dissolved in a weak acid. The question that remained was whether DNA was hiding somewhere in the tissue.

Some argued that what Schweitzer had found was the result of sample contamination, but recently completed research found ruled out the possibility of contamination and made a case for the existence of DNA in the sample.

Schweitzer first determined that the sample was indeed collagen. She and colleagues then demonstrated that the structures found within the tissue were bone cells by showing that they reacted to specific antibodies.

Upon showing that the sample contained bone cells, the research team looked for the presence of DNA by testing for an antibody that binds only to the "backbone" of DNA. The results of the test "strongly suggest that the DNA is original, but without sequence data, it is impossible to confirm that the DNA is dinosaurian," according to Tracey Peake with North Carolina State University.

"The data thus far seem to support the theory that these structures can be preserved over time," Schweitzer said of the find. "Hopefully these findings will give us greater insight into the processes of evolutionary change."

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Stephanie Grimes

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