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.
Sinocalliopteryx
Like many other theropods of the Yixian Formation, "Sinocalliopteryx" was preserved with "protofeathers," simple filamentous integument (hairlike structures covering the skin), very similar to that found in "Sinosauropteryx". The integument of "Sinocalliopteryx" differ in length across the body, with the longest protofeathers covering the hips, base of the tail, and back of the thighs. These longest protofeathers measured up to ten centimeters (4 in) in length. Protofeathers were also found on the metatarsus (upper part of the foot). While these were not nearly as long or modern as the corresponding feathers of "four-winged" dinosaurs such as "Microraptor" and "Pedopenna", they do indicate that foot-feathers or similar structures first arose in dinosaurs much more basal or "primitive" than previously known.