Psittacosaurus is a psittacosaurid ceratopsian marginocephalian dinosaur from the Early Cretaceous of Mongolia, Russia, and China. It was named in 1923 by Henry Fairfield Osborn. It is perhaps the most species-rich dinosaur genus in science; as well as this, it is one of the most extensively-studied ceratopsians, even being studied to the point where we know its color.
Psittacosaurus was a bipedal marginocephalian with a barrel-shaped body, moderately long legs with a flap of skin stretching from the creature's ankles to the base of its thick, moderately long tail, moderately long arms. Perhaps the most defining trait of this dinosaur is its round head with large jugal (cheek) horns and a small, finch-like beak in the front of its mouth; how long or round the head was varied within every species. Its body would have been covered in scaly skin, with a row of quills running down the base of its tail; one species, Psittacosaurus lujiatunensis, would have been brown in color, with a tan underside, a black face, black specks on its shoulders, and a black cloaca (excretory and reproductive organ similar to the penis of a theriiform mammal).
Psittacosaurus was an herbivore, feeding on nuts, seeds, and leaves. Its short, blunt beak was used to crack the shells of hard nuts, while the many teeth in the back of its mouth were used for shearing soft leaves.
Psittacosaurus was equipped with good olfactory senses, and its (likely) large eyes meant that it would have had acute vision; however, seeing as it was a small herbivore, these sharp senses may have evolved to help it avoid predators like Yutyrannus or Sinornithosaurus rather than to locate prey. Although there is no direct evidence for parental care in Psittacosaurus, its EQ (Encephalization Quotient, determines the possible intelligence or cognition of an animal) was shown to be a relatively high 0.31 (only slightly lower than the 0.36 of most birds, and marginally higher than the Tyrannosaurus's 0.30), and so, it is very likely that Psittacosaurus was able to build nests and care for its young; in terms of how different babies and adults were in their lifestyle, babies moved around on all fours (due to their long forelimbs), while adults were fully bipedal (due to how short their arms were, as well as their limited range of motion). As well as this, one species of Psittacosaurus, the aforementioned P.lujiatunensis, had intricate color patterns on its scales, and each distinct color brought a potential benefit for the animal; its darker-colored back and its lighter-colored underside is a great case of countershading (a method of camouflage that animals evolve in order to sneak up on prey or hide from predators more effectively), its black face may have been used for display, and the patch of black on its cloaca may have served an antimicrobial (preventing microorganisms from growing) function. A comparison of its sclerotic rings to those of modern reptiles and birds indicates that it was cathemeral.