Dinosaurs come in all sizes. The lumbering Argentinosaurus probably reached 115 feet, the winged Microraptor less than 4 feet. And today, the sole surviving lineage of dinosaurs – modern birds – includes both miniscule hummingbirds and leggy ostriches. (Learn more about why birds are actually a type of dinosaur here.) Scientists have long been interested in how non-bird dinosaurs, which include the largest land-dwelling animals that ever lived, came to have such different body sizes. The answer, of course, is through evolution, but what evolutionary changes were involved? New research helps answer that question.