This Field Museum Press Release link is a little old, but still very interesting.  What caused the holes in the back of SUE’s jaw?

SUE the T. rex is one of the most complete, best-preserved Tyrannosaurus rex specimens ever found. That level of preservation helps reveal details about SUE’s life. For instance, SUE lived to a ripe old age of about thirty-three, and in those years, suffered their fair share of injuries. SUE’s most mysterious ailment might be the holes in their jawbone. These holes, some the diameter of a golf ball, dot the back half of the left lower jaw. It’s not clear what caused them, but similar injuries have been found in other T. rex fossils. In a new study published in Cretaceous Research, scientists showed that one of the popular theories– that SUE had suffered an infection from a protozoan parasite– couldn’t be true.

“These holes in SUE’s jaw have been a mystery for decades,” says Jingmai O’Connor, the associate curator of fossil reptiles at Chicago’s Field Museum and a co-author of the study. “Nobody knows how they formed, and there have been lots of guesses.”