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.
Sinonyx
"Sinonyx" was about 1.5 m (5 ft) long, about the size of a modern grey wolf with a large elongated head, short legs and tiny hooves on all of its toes. It was built for stamina and strength and was well equipped to take care of itself by killing slower-moving prey or scavenging along sea shores. The tooth count was the primitive mammalian number (44) and the teeth were differentiated as are the heterodont teeth of today's mammals. The molars were very narrow shearing teeth, especially in the lower jaw, but possessed multiple cusps. The large skull had an extended occipital bone and large sagittal crest that contained a tiny brain. The large sagittal crest indicates a powerful bite, for these are the bones which anchor muscle to the lower jaw or mandible; with the increased surface area indicating a large muscle mass.