When people think of a "dinosaur" they often picture huge reptile-like creatures like Tyrannosaurus rex or the long-necked brachiosaurus. But there were also tiny dinosaurs.
In recent years, palaeontologists have unearthed some of the smallest dinosaurs known. In the late 1990s two tiny species of Theropods were discovered in China and Mongolia. The Theropod group contains carnivorous dinosaurs that walked on two legs, like T. rex and velociraptors. The newly discovered "tiny-osaurs" were both under two feet long and probably weighed less than your Thanksgiving turkey.
In 2002, the smallest North American dinosaur was uncovered in Alberta, Canada. This puny Theropod is also unique because it probably dined on insects. Most other Theropods were meat-eaters.
To be sure these weren't just fossils of baby dinosaurs scientist examined the growth rings in bones. In some bone tissue, layers are created as the bone grows, sort of like the rings of a tree. The bones of older animals grow more slowly, so the rings get closer together. This allows scientists to identify if the bones are from adults or juveniles.
Another way to tell is when several fossils are found together that include adults and juveniles--like the discovery of the smallest Sauropod species in Germany in 2006.
The Sauropod group contains the giant, long-necked, plant-eating dinosaurs that walked on four legs--like the eighty-foot long brachiosaurus. But the new species from Germany are much smaller--about twenty feet long as adults, and some juveniles are only four feet long.