Body mass is a fundamental factor in determining how much food an animal requires, how it moves and grows, and what role it plays in its ecosystem. Measuring modern animals is often a straightforward matter of putting them on a scale, but it’s no easy feat for paleontologists interested in extinct creatures like dinosaurs, since many of these animals’ weighty parts — their organs, muscles and skin, for example — are long gone. Frequent claims of “the heaviest dinosaur of all time,” for example, as in the case of the recently named Patagotitan, are fraught with uncertainty. Recent research, however, is offering a novel approach to estimating dinosaur body masses by examining the footprints they left behind.