Psittacosauridae
Skeletal reconstruction of Psittacosaurus
The Psittacosauridae are a taxon ( a systematic group) the bird Beck dinosaur from the group of ceratopsians. For a long time only the species-rich genus Psittacosaurus was classified into this group, but with the little-known Hongshanosaurus a second species was described in 2003.
Features
The Psittacosauridae are characterized among other things by the following features: Situated in front of the eye socket of the skull is very short, the nasal cavities are far above, the location before the eye socket skull window is closed, the fourth finger is reduced and consists of only one phalanx ( Phalange ), and the fifth finger is missing.
Psittacosauridae were rather small (up to 2 meters long ), mainly on the back legs ( biped ) Locomotive dinosaurs. As with all Ceratopsia was located at the tip of the upper jaw a Rostralknochen, constituting with the small square of the mandible Prädentale the typical " parrot beak". Like all ceratopsians they were herbivores.
All finds of Psittacosauridae originate from the Lower Cretaceous and are about 134 to 100 million years old. All the fossils were found in East Asia, mainly in China and Mongolia.
System
Apart from the primitive Yinlong the Psittacosauridae form the sister group of the other, summarized as Neoceratopsia Ceratopsia. This comes in the following cladogram expressed:
Psittacosauridae
Neoceratopsia
Yinlong
There is disagreement about the position of Chaoyangsaurus and the closely related Xuanhuaceratops that Chaoyangsauridae. After You and Dodson (2004) is Chaoyangsaurus a primitive representative of the Neoceratopsia, the describer of Xuanhuaceratops, Zhou et al. (2006) organize these and Chaoyangsaurus contrast, in the pedigree as basal ceratopsians and thus primitive than the Psittacosauridae one.