Psittacosaurus lujiatunensis, named in 2006 by Chinese paleontologist Zhou Chang-Fu and 3 Chinese colleagues, is one of the oldest known species, based on four skulls from the lower beds of Yixian Formation of Liaoning Province, near the village of Lujiatun. This bed has been dated differently by different authors, from 128 Ma in the Barremian stage, to 125 Ma in the earliest Aptian. P. lujiatunensis was contemporaneous with another psittacosaurid species, Hongshanosaurus houi, which was found in the same beds. It is potentially synonymous with H. houi; Sereno (2010), who proposed that Hongshanosaurus is a synonym of Psittacosaurus, opted to leave P. lujiatunensis and H. houi separate species due to the inadequacies of the latter's type specimen.
The type skull of P. lujiatunensis measures 19 cm (7.5 in) in length, while the largest known skull is 20.5 centimeters (8 in) long, so this species was similar in size to P. mongoliensis and P. sibiricus. There is a fossa in front of the eye, as in P. mongoliensis. The jugal bones flare outwards widely, making the skull wider than it is long, as seen in P. sinensis. Widely flared jugals are also found in P. sibiricus and P. major. P. lujiatunensis lacks the postorbital horns seen in P. sinensis or P. major. Overall, this species is thought to exhibit several primitive characteristics compared to other species of Psittacosaurus, which is consistent with its greater geological age.
Read more about this topic: List Of Psittacosaurus Species