How is it possible for soft tissue to survive in dinosaur fossils?

When you picture dinosaur fossils, bones are likely the first thing that comes to mind, along with the scientific puzzle of reconstructing them to understand what happened to the soft parts. Finding dinosaur blood buried in your backyard would be quite the surprise. And if you were to immerse a dinosaur bone in acid, you wouldn’t expect it to dissolve into soft tissue.

But could it?

In 2005, a paper titled 'Soft tissues are preserved within hindlimb elements of Tyrannosaurus rex' sparked a heated debate, published by a team of paleontologists from North Carolina State University in the journal Science.

Mary Schweitzer and her research team submerged a fossilized T. rex bone fragment in an acidic demineralizing solution to examine its components. If the fossil had been pure rock, the solution would have completely dissolved it. However, it preserved soft tissue, which, upon closer inspection, was identified as blood vessels, bone matrix, and osteocytes (cells that form bone) from a dinosaur that lived 68 million years ago. For more on the study and the controversy it sparked, read How did scientists find soft tissue in dinosaur fossils?

While many theories exist about how soft tissue could survive for 68 million years, Schweitzer suggested that the bone's dense mineralization might have shielded the inner tissue. In some instances, however, dinosaur soft tissue fossilized alongside the bones. For example, in 2000, paleontologists uncovered a 77-million-year-old Brachylophosaurus canadensis, and found its skin, scales, muscle, footpads, and even stomach contents preserved as fossils.

Soft tissue fossilization is exceedingly rare due to decomposition and scavenging. Most often, dinosaur flesh was consumed by other animals or decayed under the sun. Occasionally, however, sediment would cover the remains, allowing the slow process of fossilization to begin.

Soft tissue fossilization is more common in creatures that lived in sediment, such as trilobites, a type of seafloor arthropod. In contrast, large terrestrial animals like dinosaurs would require a rare, catastrophic event, like being buried by a landslide, to be fossilized in such a way.

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