Эрте крест кезеңінің Psittacosaurus динозавры

Early Cretaceous dinosaur genus

Psittacosaurus (,/s//ɪ//t//ə//k//ə/'/s//ɔːr//ə//s/ SITə kəSORəs; "parrot lizard") is a genus of extinct ceratopsian dinosaur from the Early Cretaceous of what is now Asia, existing between 126 and 101 million years ago. It is notable for being the most species rich non avian dinosaur genus. Up to 12 species are known, from across China, Mongolia, Russia, and Thailand. The species of Psittacosaurus were obligate bipeds at adulthood, with a high skull and a robust beak. One individual was found preserved with long filaments on the tail, similar to those of Tianyulong. Psittacosaurus probably had complex behaviours, based on the proportions and relative size of the brain. It may have been active for short periods of time during the day and night, and had well developed senses of smell and vision. Psittacosaurus was one of the earliest ceratopsians, but closer to Triceratops than Yinlong. Once in its own family, Psittacosauridae, with other genera like Hongshanosaurus, it is now considered to be senior synonym of the latter and an early offshoot of the branch that led to more derived forms. The genera closely related to Psittacosaurus are all from Asia, with the exception of Aquilops, from North America. The first species was either P. lujiatunensis or closely related, and it may have given rise to later forms of Psittacosaurus. Psittacosaurus is one of the most completely known dinosaur genera. Fossils of hundreds of individuals have been collected so far, including many complete skeletons. Most age classes are represented, from hatchling through to adult, which has allowed several detailed studies of Psittacosaurus growth rates and reproductive biology. The abundance of this dinosaur in the fossil record has led to the labelling of Lower Cretaceous sediments of east Asia the Psittacosaurus biochron.

In 1922, American paleontologist Henry Fairfield Osborn took part in the Third Asiatic Expedition of the American Museum of Natural History to discover fossils and geologic formations from the Cretaceous and Tertiary of Mongolia. In the Oshih Formation of the Artsa Bogdo Basin, Wong, the Mongolian chauffeur, discovered a nearly complete skull, jaws, and skeleton of a dinosaur, which was given the nickname of "Red Mesa skeleton". The location of discovery is also known as the Oshih locality of the Khukhtek Formation, of Early Cretaceous Aptian to Albian age. Following the discovery of material of psittacosaurids in Haratologay in Inner Mongolia, Yang Zhongjian described two additional species in 1932. Known from a crushed skull and fragmentary lower jaw, Young named Psittacosaurus osborni, distinguished by its small size and lack of a sagittal crest on the parietal. The second species, P. tingi, was named for partial lower jaws and teeth, which Young only tentatively referred to Psittacosaurus instead of Protiguanodon. Both specimens, stored in the Institute of Vertebrate Paleontology and Paleoanthropology as IVPP RV31039 and IVPP RV31040 respectively, come from the Xinpongnaobao Formation. An additional tooth, partial hand, and fragments of vertebrae and limbs were found in the same locality, with the tooth being referred to Protiguanodon and the remainder of the material being uncertain. Further discoveries in the Qingshan Formation of Laiyang in 1958 were described by Zhao Xijin in 1962, giving the new name Psittacosaurus youngi for the specimen BPV.149 in the Beijing Museum of Natural History. Known for a complete skull, partial vertebral series and partial pelvis, P. youngi was distinguished by Zhao by having the shortest skull of all species, vertebral and tooth counts, and various features of the skull and skeleton. P. youngi was considered to be most similar to P. sinensis, but separated them to bring the count of members of Psittacosauridae to one genus and five species. While it differs from the type specimen of P. mongoliensis, it falls within the range of individual variation seen in other specimens of that species and is no longer recognised as a valid species. This is the highest number of valid species currently assigned to any single non avian dinosaur. In contrast, most other dinosaur genera are monospecific, containing only a single known species. The difference is most likely due to artifacts of the fossilisation process. While Psittacosaurus is known from hundreds of fossil specimens, most other dinosaur species are known from far fewer, and many are represented by only a single specimen. With a very high sample size, the diversity of Psittacosaurus can be analysed more completely than that of most dinosaur genera, resulting in the recognition of more species. Most extant animal genera are represented by multiple species, suggesting that this may have been the case for extinct dinosaur genera as well, although most of these species may not have been preserved. In addition, most dinosaurs are known solely from bones and can only be evaluated from a morphological standpoint, whereas extant species often have very similar skeletal morphology but differ in other ways which would not normally be preserved in the fossil record, such as behaviour, or colouration. Therefore, actual species diversity may be much higher than currently recognised in this and other dinosaur genera. As some species are known only from skull material, species of Psittacosaurus are primarily distinguished by features of the skull and teeth. Several species can be recognised by features of the pelvis as well. However, the type specimen of P. youngi (a partial skeleton and skull) was discovered in the same rocks as P. sinensis and appears to be very similar, so P. youngi is generally considered a junior synonym of that better known species. Several individuals of different ages were discovered in the early 1970s by Chinese paleontologists and described by Sereno and Zhao, although the holotype and most complete skeleton belonged to a juvenile. An adult skeleton was later discovered at a different locality in Xinjiang. P. sattayaraki
French paleontologist Eric Buffetaut and a Thai colleague, Varavudh Suteethorn, described a partial upper and lower jaw from the Aptian Albian Khok Kruat Formation of Thailand in 1992, giving it the name P. sattayaraki. In 2000, Sereno questioned the validity of this species, citing its eroded and fragmentary nature, and noted an absence of features characteristic of the genus Psittacosaurus. Other authors have also defended its validity, Unfortunately, the skull was damaged while in the care of the Chinese Institute of Vertebrate Paleontology and Paleoanthropology (IVPP), and several fragments have been lost, including all of the teeth. Sereno suggested in 2000 that P. mazongshanensis was a nomen dubium, with no unique features that separate it from any other species of Psittacosaurus. The remains were not completely described until 2006. Two nearly complete, articulated skeletons and a variety of disarticulated material from other individuals of all ages are known from the Ilek Formation of Siberia, Individuals of this species could grow up to 2.5 meters in length, making it one of the largest members of the genus. P. lujiatunensis
P. lujiatunensis, named in 2006 by Chinese paleontologist Zhou Chang Fu and three Chinese and Canadian colleagues, is one of the oldest known species, based on four skulls from the lower beds of the Yixian Formation, near the village of Lujiatun. 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. Nearly 100 Psittacosaurus skeletons were excavated in Mongolia during the summers of 2005 and 2006 by a team led by Mongolian paleontologist Bolortsetseg Minjin and American Jack Horner from the Museum of the Rockies in Montana. Although only P. mongoliensis has been described from Mongolia so far, these specimens are still in preparation and have not yet been assigned to a species.