Resource: T. Rex Blood?

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The remains of organisms that have been preserved as fossils offer a glimpse into geological time, but the fossilization process does not typically preserve soft tissues (such as muscles and skin), which contain important biological information. As a result, scientists have only a limited view of the organisms and conditions of the past. However, in 2005, a group of researchers led by paleontologist Dr. Mary Schweitzer announced a surprising discovery that opened up a new window into the past—soft tissue preserved within a 68 million-year-old Tyrannosaurus rex fossil!

For an organism to become part of the fossil record, the time between its death and its burial in sediment needs to be rapid; if not, scavengers, bacteria, and weathering processes will destroy it completely. Once buried, according to the conventional theory of fossil formation, groundwater percolates through the remains and minerals fill the empty spaces in the hard parts of the organism (such as bones and teeth), fossilizing them, while the soft tissues decay.

Scientists usually take great care to preserve the integrity of their fossil finds; however, Dr. Schweitzer saw something interesting within some fragments of a T. rex bone she had been given and decided to employ an unusual method to investigate. To get a closer look at the bone structure, she placed a fragment in a weak acid solution to partially destroy it. When her team removed the fragment from the solution, they were surprised at what they saw. It appeared that the mineral removal process had left behind intact, pliable soft tissue that seemed to contain blood vessels and cells. This was a seemingly impossible discovery. With skepticism and scientific curiosity, they repeated the process with other fragments and duplicated their findings.

When they published their results, the scientific community was fittingly shocked. It was generally accepted that there was no way soft tissue could survive millions of years. It had long been believed that fossils were completely made of minerals—that if left to soak in an acid solution that dissolved minerals, the entire fossil would dissolve. The discovery of soft tissue meant that the theory of fossilization would need to be reconsidered, and it opened up a new area of research that hadn't previously been thought possible.

Since the initial discovery, Dr. Schweitzer has continued to pioneer this emerging area of research that combines paleontology and molecular biology. Collaborating with colleagues with different areas of expertise (for example, a specialist in techniques to analyze protein sequences), she has found further evidence to support the initial findings. Scientific tests identified the existence of collagen protein, which was then sequenced and compared against the protein sequences of other animals. The scientists observed similarities between the structure of dinosaur collagen and the sequences found in chickens, frogs, and newts. However, controversy still exists over whether soft tissue has been found in fossils at all. In 2008, another team of scientists reported evidence that the flexible material found inside fossils was actually biofilm—basically, slime created by bacteria—that was formed in modern times.

To learn more about fossils, check out How a Dinosaur Became a Fossil and Fossils.

To learn more about dinosaurs, check out Fossilized Dinosaur Bones and What Killed the Dinosaurs?.

To learn more about scientific discovery, check out Scientific Processes.

To learn more about the geological timeline, check out Deep Time.

Print Questions for Discussion

• Did Dr. Mary Schweitzer originally set out to look for dinosaur soft tissue? If not, how did she arrive at her discovery?
• What is medullary tissue? Why does it make sense that dinosaur bones share some features with bird bones?
• Why do you think scientists haven't found soft tissue in fossils before?
• Why do you think this finding is important? Why is it controversial?
• Can you think of how you might try to resolve this controversy?