Fossil footprints show dinosaur ancestors learning to walk tall, step by step

Footprints pressed into stone more than 240 million years ago are rewriting a posture change. Researchers led by Lorenzo Marchetti of Berlin's natural history museum compared trackways from the Permian and Triassic periods and found a gradual shift — from sprawling walks to upright stances, longer middle toes and smaller hands — in the relatives of dinosaurs. Those small steps in stone were essential groundwork for the two-legged giants to come.