Psittacosaurus Trinity

- P. mongoliensis (Osborn, 1923) is the type species. Its skull (the adult one, not the holotype because it's a subadult) is 19,7 cm long, flat on top, especially over its posterior part, with a triangular antorbital fossa (on the outside maxillar surface). It is also one of the biggest species known, with a femural length of about 21 cm in adults;

- P. major (Sereno et al., 2007) has a skull that is proportionally bigger than that of P. mongoliensis (20,3 cm long). The snout in this species is very narrow and jugal horns are well-developped and slightly downwards instead of directly outwards. The dentary flange is very prominent and the femur is 19,7 cm long;

- P. sibiricus (Voronkevich & Averianov, 2000) is a very particular species and also the largest one of the genus, with a skull 20,7 cm long and a 22,3 cm long femur. The skull shows a horn in fron of the eyes, three well-developped postorbitals horns, and directly outwards jugal horns.