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List of Psittacosaurus species
Seventeen species have been assigned to the extinct ceratopsian dinosaur genus ''Psittacosaurus'', although only nine to eleven are considered valid.〔Xu Xing & Zhao Xijin. (1999). Psittacosaur fossils and their stratigraphical implications. In: Wang Y. & Deng T. (Eds.). ''Proceedings of the Seventh Annual Meeting of the Chinese Society of Vertebrate Paleontology''. Beijing: China Ocean Press. Pp. 75–80.〕〔Averianov, Alexander O., Voronkevich, Alexei V., Leshchinskiy, Sergei V. & Fayngertz, Alexei V. (2006). A ceratopsian dinosaur ''Psittacosaurus sibiricus'' from the Early Cretaceous of West Siberia, Russia and its phylogenetic relationships. ''Journal of Systematic Paleontology'' 4(4): 359-395. 〕〔Hai-Lu You, Kyo Tanoue & Peter Dodson. (2008). (New data on cranial anatomy of the ceratopsian dinosaur ''Psittacosaurus major'' ). ''Acta Palaeontologica Polonica'' 53(2):183–196.〕〔Sereno, Paul C. (2010). Taxonomy, cranial morphology, and relationships of parrot-beaked dinosaurs (Ceratopsia:''Psittacosaurus''). In: Ryan, Michael J., Chinnery-Allgeier, Brenda J. & Eberth, David A. (Eds.). ''New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium''. Bloomington and Indianapolis: Indiana University Press. Pp. 21–58. ISBN 978-0-253-35358-0〕 This is the greatest number of valid species assigned to any single dinosaur genus (not including birds).〔Sereno, Paul C. (1997). Psittacosauridae. In: Currie, Phil J. & Padian, Kevin P. (Eds.). ''The Encyclopedia of Dinosaurs''. Berkeley: University of California Press. Pp. 611-613.〕 By contrast, most dinosaur genera contain only a single species.
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 recognized by features of the pelvis as well.〔Brinkman, Donald B., Eberth, David A., Ryan, M.J. & Chen Peiji. (2001). The occurrence of ''Psittacosaurus xinjiangensis'' Sereno and Chao, 1988 in the Urho area, Junggar basin, Xinjiang. ''Canadian Journal of Earth Sciences'' 38: 1781-1786.〕 Overall size estimates of most species have not been published or are unavailable due to lack of fossil preservation. However, measurements of the skull or femur have been published for all well-established species and can be used as a basis for comparison. Species are listed in the order in which they were described, except for synonyms, which are described with the senior synonym.
==''Psittacosaurus mongoliensis'' (type)==
''Psittacosaurus mongoliensis'' is the type species of the genus, named by American paleontologist Henry Fairfield Osborn in 1923. Remains of this dinosaur were first discovered the year before, on the third American Museum of Natural History expedition to the Gobi Desert of Mongolia, when one of the expedition's drivers found the type specimen (AMNH 6254).〔Osborn, Henry F. (1923). Two Lower Cretaceous dinosaurs of Mongolia. ''American Museum Novitates'' 95: 1-10.〕 This same expedition turned up the remains of many other famous Mongolian dinosaurs, including ''Protoceratops'', ''Oviraptor'', and ''Velociraptor''.〔Osborn, Henry F. (1924). Three new Theropoda, ''Protoceratops'' zone, Central Mongolia. ''American Museum Novitates'' 144: 1-12.〕 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 Ma (million years ago). Fossil remains of over 75 individuals have been recovered, including nearly 20 complete skeletons with skulls.〔You Hailu & Dodson, Peter. (2004). Basal Ceratopsia. In: Weishampel, David B., Dodson, Peter, & Osmólska, Halszka. (Eds.). ''The Dinosauria'' (2nd Edition). Berkeley: University of California Press. Pp. 478-493.〕 Individuals of all ages are known, from hatchlings less than 13 centimeters (5 in) long, to very old adults reaching nearly 2 meters (6.5 ft) in length.〔Coombs, Walter P. (1982). Juvenile specimens of the ornithischian dinosaur ''Psittacosaurus''. ''Palaeontology'' 25: 89-107.〕
Skulls of ''P. mongoliensis'' are flat on top, especially over the back of the skull, with a triangular depression, the antorbital fossa, on the outside surface of the maxilla (an upper jaw bone). A flange is present on the lower edge of the dentary (the tooth-bearing bone of the lower jaw), although it is not as prominent as in ''P. meileyingensis'' or ''P. major'' (=''P. lujiatunensis''). ''P. mongoliensis'' is among the largest known species. The skull of the type specimen, which is probably a juvenile,〔Russell, Dale A. & Zhao Xijin. (1996). New psittacosaur occurrences in Inner Mongolia. ''Canadian Journal of Earth Sciences'' 33: 637-648.〕 is 15.2 centimeters (6 in) long, and the associated femur is 16.2 centimeters (6.4 in) in length.〔Osborn, Henry F. (1924). ''Psittacosaurus'' and ''Protiguanodon'': Two Lower Cretaceous iguanodonts from Mongolia. ''American Museum Novitates''. 127: 1-16.〕 Other specimens are larger, with the largest documented femur measuring about 21 centimeters (8.25 in) long.〔Erickson, Gregory M. & Tumanova, Tatyana A. (2000). Growth curve of ''Psittacosaurus mongoliensis'' Osborn (Ceratopsia: Psittacosauridae) inferred from long bone histology. ''Zoological Journal of the Linnean Society'' 130: 551–566.〕
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