Answer:
The largest 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
large school buses and the height of a four-story
building).
Fragmentary leg bones and vertebrae of even larger
dinosaur species are known, but these skeletal remains
are too incomplete to determine their exact size.
Several of these (Argentinasaurus and
Amphicoelias) might have been one and a half to two
times larger than Brachiosaurus.
The smallest dinosaurs were just slightly larger
than a chicken; Compsognathus ("pretty jaw") was 1 m
(3 ft) long and probably 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 type that was much larger than
Compsognathus when fully grown.
If birds are advanced dinosaurs, then the
smallest dinosaur would be the hummingbird!
