Psittacosaurus lacked the expressive horns and neck collars that are a characteristic feature of Triceratopos, Styracosaurs, and other horned dinosaurs. However, numerous structural features of psittacosaurs allow us to consider them as early representatives of this group.
All dinosaurs belonging to the ceratopsian family had a strongly curved beak, similar to a parrot’s beak. The beak was covered with a rough cornea and was ideal for plucking leaves and plant stems.
The upper part of the beak consisted of a special bone called the rostrum, which is found only in this group of animals. Psittacosaurus had the rudiments of a neck collar formed by a small protrusion of bone at the base of the skull, as well as unusual prominent cheekbones. The function of these cheekbones is unclear, but they are present in all horned dinosaurs.
It is possible that during the tournaments, the males grappled with these protrusions and measured their strength, pushing the opponent. Such competitions played an important role in the struggle for females, for territory and influence.
Unlike the horned dinosaurs that appeared later, Psittacosaurus was a small, light, even graceful animal that moved only on its hind legs. On the front limbs he had thin long fingers with sharp claws, with which he collected food. The hind legs of Psittacosaurus were long and slender, which allowed it to run fast enough.
Psittacosaurus chewed food in a rather unusual way. They didn’t move their jaws up and down like scissors like other dinosaurs did. The lower jaw of the psittacosaurus could move back and forth relative to the upper jaw, like a millstone mill, perfectly grinding food.
In several psittacosaurs found, near the bones of the skeleton in the peritoneum, placers of small, smoothly polished stones were found. Apparently. Psittacosaurus deliberately swallowed small pebbles that grew into the walls of the stomach. The contractions of the muscles of the stomach set the stones in motion, and they rubbed the plant mass, facilitating its digestion. Scientists call these stones gastroliths.
Psittacosaurus is the only ornithischian known to have used gastroliths, although there is evidence that Stegosaurus may have used this technique as well. Gastroliths found in the stomach region of some prosauropods, sauropods, and theropods. Scientists are confident that the stones found in the stomach of dinosaurs acted exactly as described, because many modern birds, such as chickens and ostriches, use gastroliths for the same purpose.