Dinosaurs became giants — so why did they never become tiny?

The absence of tiny dinosaurs may be just as interesting as the existence of giant ones. "If we want to understand how today's biodiversity evolved, we need to understand why tiny dinosaurs appear to have been missing." Instead, the fossil evidence indicates that genuinely tiny dinosaurs outside the bird lineage were either extremely uncommon or may not have existed at all. Birds evolved from dinosaurs, but modern birds can reach sizes far below those known for dinosaurs outside the bird lineage. The living descendants of dinosaurs -- birds -- they can be tiny.