Sinosauropteryx
"Sinosauropteryx" was a small theropod with an unusually long tail and short arms. The longest known specimen reaches up to in length, with an estimated weight of It was a close relative of the similar but older genus "Compsognathus", both genera belonging to the family Compsognathidae. Only one species of "Sinosauropteryx" has been named: "S. prima", meaning "first" in reference to its status as the first feathered non-avialian dinosaur species discovered. Three specimens have been described. The third specimen previously assigned to this genus represents either a second, as-yet unnamed species or a distinct, related genus.
Dinosaur size
"Tyrannosaurus" was for many decades the largest theropod and best-known to the general public. Since its discovery, however, a number of other giant carnivorous dinosaurs have been described, including "Spinosaurus", "Carcharodontosaurus", and "Giganotosaurus". These large theropod dinosaurs rivaled or even exceeded "Tyrannosaurus" in size, though more recent studies show some indication that "Tyrannosaurus", although shorter, was the heavier predator. There is still no clear explanation for exactly why these animals grew so much larger than the land predators that came before and after them.