Which was the smallest dinosaur?

The smallest dinosaurs were just slightly larger than a chicken. Compsognathus (meaning “pretty jaw”) was 3 feet (1 meter) long and probably weighed about 6.5 pounds (2.5 kilograms). At one time, scientists thought that Mussaurus (meaning “mouse lizard”) was the smallest dinosaur, but it is now known to be the hatchling of a dinosaur type that was much larger than Compsognathus when fully grown.

If birds are advanced dinosaurs, as some scientists believe, then the smallest dinosaur would be the hummingbird!