For more than a century, paleontologists have held the bones of Tyrannosaurus rex in their hands without ever finding the mark its foot left in the earth — until a high school science teacher, walking a North Dakota landscape with students, looked down and saw what no one had seen before. The first documented T. rex trackway in the geological record was not found by a funded expedition but by the kind of attentive curiosity that good teachers carry into the field. Sixty-six million years after the animal walked, its stride length, its weight, its gait — the living facts of its movement — have