What was the biggest dinosaur? What was the smallest?

The biggest complete dinosaur we know of was Brachiosaurus (arm lizard); it reached 23 m in length and 12 m in height (about the length of two big school buses and the height of a four-story building). Fragmentary leg bones and vertebrae of even bigger dinosaur species are known, but these skeletal ruins are too incomplete to determine their precise size. Numerous of these (Argentinasaurus and Amphicoelias) might have been one and a half to two times larger than Brachiosaurus.

The smallest dinosaurs were just faintly larger than a chicken; Compsognathus (pretty jaw) was 1 m (3 ft) long and possibly weighed about 2.5 kg (about 6.5 lb). These three dinosaur types all lived during the Jurassic Period. Mussaurus (mouse lizard) was claimed as the smallest dinosaur, but it is now known to be the hatchling of a dinosaur category that was much larger than Compsognathus when completely grown. If birds are advanced dinosaurs, then the minimum dinosaur would be the hummingbird!