Tens of millions of years after the largest Tyrannosaurus rex ever discovered drew its last breath, science has finally learned why: a broken rib, revealed through a rare convergence of preserved soft tissue and neutron imaging technology. The fossil, already remarkable for its sheer scale, now offers something far rarer than size — a glimpse into the specific, mortal vulnerability of a creature that ruled its world. In the long story of life on Earth, even the mightiest are undone not by their smallness, but by a single fracture in the architecture that held them together.