When paleontologists find fossilized dinosaur bones during a dig, they usually do everything in their power to protect them, using tools like toothbrushes to carefully unearth the bones without inflicting any damage. However, when scientists found a massive Tyrannosaurus rex thigh bone in a remote region of Montana a few months ago, they were forced to break the bone in two in order to fit it into the transport helicopter. This act of necessity revealed a startling surprise: soft tissue that had seemingly resisted fossilization still existed inside the bone. This tissue, including blood vessels, bone cells, and perhaps even...