Living during the Early Cretaceous (~126-101 mya) in Mongolia, Siberia, and China, Psittacosaurus (meaning “parrot lizard”) represents an early specialized offshoot of the ceratopsians – it wasn’t directly ancestral to any of the later forms, instead being more of an evolutionary cousin.
It’s one of the most well-studied of all non-avian dinosaurs, represented by hundreds of fossils at all ages from hatchlings to adults. A large number of species have been named within the genus, although there’s disagreement about how many are actually valid, and even some of the best-preserved specimens still haven’t been given an official species classification.
Growing up to about 2m long (6′6″), it had sideways-flaring cheek horns and little-to-no frill, and only four fingers on its hands instead of the five seen in all other ceratopsians. One fossil preserves an amazing level of soft-tissue detail, showing the outline of the body, a row of long bristles, skin membranes running from its ankles to the base of its tail, and even evidence of the countershaded color pattern the animal had in life.
While adults were fully bipedal, hatchlings and juveniles seem to have moved around on all fours – suggesting that some of their direct ancestors may have evolved to be quadrupedal before secondarily re-acquiring two-legged locomotion.