How did scientists find soft tissue in dinosaur fossils?

By: Tracy V. Wilson

These pieces of petrified wood, found in Petrified Forest National Park, used to be trees. Now they're rocks -- good for paperweights but bad for paper. See more dinosaur pictures.
iStockphoto/Tom Marvin

­­­Fossilization is a real-world Medusa -- it turns living things to stone. Take petrified wood as an example. If a tree dies and is buried in sediment, the sediment protects the wood while mineral-laden groundwater seeps through it. The minerals gradually r­eplace the wood, leaving a rocky facsimile behind.

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The same thing happens when more complex organisms, like animals, become fossils. Anything that's stretchy, squishy, watery or rubbery decays while minerals reinforce the bones, turning them to stone. Even in the case of "mummified" fossil finds, the preserved skin and other organs aren't soft anymore. In fossils like these, the body was protected from decay long enough for minerals to replace the soft tissues faster than they could decay. The soft tissues themselves are completely gone, and only stone remains.

­At least, that's the conventional wisdom. But in 2005, a paper appeared in the journal Science that challenged the basic principles of fossilization from­ its very first sentence: "Soft tissues are preserved within hindlimb elements of Tyrannosaurus rex" [source: Schweitzer, 3/25/2005]. The paper goes on to describe blood vessels, bone matrix and elastic tissues, all found somewhere they shouldn't be.

According to the long-held view of fossilization, the presence of those types of tissue in a fossil is impossible. The paper's primary author, Mary Higby Schweitzer, had come to this unconventional conclusion by approaching her research in an unconventional way. In addition to sparking controversy in the scientific community, her find had implications for some religious communities.

So how did she find stretchy tissue in a rocky bone, and what do ostriches have to do with it? What kind of analysis supports her assertion that she's found 65-million-year-old soft tissue? Next, we'll take a look at how Schweitzer unveiled her samples and what happenstance had to do with this groundbreaking find.