Psittacosaurus (/ˌsɪtəkəˈsɔːrəs/ SIT-ə-kə-SOR-əs; "parrot lizard")[1] is a genus of extinct ceratopsian dinosaur from the Early Cretaceous of what is now Asia, existing between 125 and 105 million years ago.

Osborn demonstrated the taxon was unique based on the short and deep snout, and the broad rear skull, as well as by lacking teeth in the premaxilla.

[2] In the same paper, Osborn also described another new taxon he considered similar to Psittacosaurus, Protiguanodon mongoliense, which was found in the same expedition but from the Ondai Sair Formation.

[2] Osborn published an additional description of the specimens of Protiguanodon and Psittacosaurus in 1924, citing his previous study as naming both to be members of Psittacosauridae, and considering the separate status of Protiguanodontinae as uncertain.

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.

In 1946 they discovered a new locality, Ulan Osh, where a disarticulated specimen of Psittacosaurus mongoliensis was found, and in 1948 they revisited the sites of the American expeditions and excavated fragmentary postcrania from Oshih and Ondai Sair.

Of this material, the nearly complete skeleton and skull IVPP V738 was described as the type of the new species Psittacosaurus sinensis, which was found in a red layer 10 mi (16 km) northwest of Rongyang City in Shandong.

[9] 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.

[11] Many later expeditions by various combinations of Mongolian, Russian, Chinese, American, Polish, Japanese, and Canadian paleontologists also recovered specimens from throughout Mongolia and northern China.

In these areas, Psittacosaurus mongoliensis fossils are found in most sedimentary strata dating to the Aptian to Albian stages of the Early Cretaceous Period, or approximately 125 to 100 mya.

[21] 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.

[20] A second species described in 1988 by Sereno and Zhao, along with two Chinese colleagues, was P. meileyingensis from the Jiufotang Formation, near the town of Meileyingzi, Liaoning Province, northeastern China.

[23] 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.

[18] However, in 2002 the original authors published new images of the fossil which seem to show teeth in the lower jaw that exhibit the bulbous vertical ridge characteristic of psittacosaurs.

[18] However, more recent authors have noted that it can be distinguished by its proportionally long snout compared to other species of Psittacosaurus, as well as a prominent bony protuberance, pointing outwards and downwards, on the maxilla of the upper jaw.

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,[26] which ranges from the Barremian to Aptian stages of the Early Cretaceous.

[4] One nearly complete skeleton of P. lujiatunensis from the same lower beds of the Yixian Formation had previously been classified in its own species, Psittacosaurus major, named for the large size of its skull by Sereno, Zhao and two colleagues in 2007.

[40][41][42] 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.

A series of what appear to be hollow, tubular bristle-like structures, approximately 16 centimetres (6.3 in) long, were also preserved, arranged in a row down the dorsal (upper) surface of the tail.

The skin remains could be observed by a natural cross-section to compare them to modern animals, showing that dinosaurian dermal layers evolved in parallel to those in many other large vertebrates.

The specimen also had dense clusters of pigment on its shoulders, face (possibly for display), and cloaca (which may have had an antimicrobial function, though this has been disputed[52]), as well as large patagia on its hind legs that connected to the base of the tail.

[53][54][55] The authors were unable to determine which species of Jehol Formation Psittacosaurus the specimen belonged to due to the way the skull is preserved, but ruled out P. mongoliensis, based on hip features.

[52] A 2022 study of SMF R 4970 identified it as an approximately 6–7 year old subadult by comparing its femoral length to that of similarly-aged specimens of P. lujiatunensis, and found that it preserves the first umbilicus (belly button) known from a non-avian dinosaur (the oldest known from an amniote).

The orbit (eye socket) is roughly triangular, and there is a prominent flange on the lower edge of the dentary, a feature also seen in specimens of P. lujiatunensis, and to a lesser degree in P. mongoliensis, P. sattayaraki, and P.

In addition, the antorbital fenestra, an opening in the skull between the eye socket and nostril, was lost during the evolution of Psittacosauridae, but is still found in most other ceratopsians and in fact most other archosaurs.

[65] Stegoceras Yinlong Xuanhuaceratops Chaoyangsaurus P. sinensis P. mongoliensis Liaoceratops Aquilops Auroraceratops Yamaceratops Helioceratops Archaeoceratops Koreaceratops Leptoceratopsidae Coronosauria Although many species of Psittacosaurus have been named, their relationships to each other have not yet been fully explored and no scientific consensus exists on the subject.

[46] An age determination study performed on the fossilized remains of P. mongoliensis by using growth ring counts suggest that the longevity of the basal ceratopsian was 10 to 11 years.

[46] The find of a herd of six Psittacosaurus individuals killed and buried by a volcanic mudflow indicates the presence of at least two age groups from two distinct clutches gathered together.

[12][41][43] All Psittacosaurus fossils discovered so far have been found in Early Cretaceous sediments in Asia, from southern Siberia to northern China, and possibly as far south as Thailand.

The most common age of geologic formations bearing Psittacosaurus fossils is from the late Barremian through Albian stages of the Early Cretaceous, or approximately 125 to 105 mya (million years ago).