TULSA, Okla. (AP) — Lately, museums all over the U.S. and Canada have sent pieces of their T. rex skeletons to Dr. Holly Ballard's lab at Oklahoma State University's Health Sciences Center in Tulsa.

When Ballard returns the fossils, they're missing small sections, which she slices out of the bone to mount on microscope slides, then replaces with plastic casts. But the fossils go home with stories to tell, because from those thin slices of bone, Ballard learns how old each dinosaur was when it died, how quickly it grew, and maybe even a few tidbits about its health — exactly the kind of things...