Species of Psittacosaurus

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Over a dozen extinct species have been referred to the ceratopsian dinosaur genus Psittacosaurus, although only seven to nine are considered valid today.^[1] This is the highest number of valid species currently assigned to any single dinosaur genus (not including birds).^[2] 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 the configuration of the bones of the skull, as well as features of the teeth. However, several species can be recognized by features of the pelvis as well.^[3] Overall size estimates of most species have not been published or are unavailable due to lack of fossil preservation. However, skull or femur measurements have been published for all well-established species and can be used as a basis for comparison.

Contents 1 Psittacosaurus mongoliensis 2 Protiguanodon mongoliense 3 Psittacosaurus protiguanodonensis 4 Psittacosaurus osborni 5 Psittacosaurus tingi 6 Psittacosaurus sinensis 7 Psittacosaurus youngi 8 Psittacosaurus guyangensis 9 Psittacosaurus meileyingensis 10 Psittacosaurus xinjiangensis 11 Psittacosaurus sattayaraki 12 Psittacosaurus neimongolensis 13 Psittacosaurus ordosensis 14 Psittacosaurus mazongshanensis 15 Psittacosaurus sibiricus 16 Unassigned specimens 17 References 18 External links

[edit] Psittacosaurus mongoliensis

P. mongoliensis is the type species of the genus, named by Henry Fairfield Osborn in 1923.^[4] It is the largest, as well as the most completely known. Fossil remains of over 75 individuals have been recovered, including nearly 20 complete skeletons with skulls.^[5] Individuals of all ages are known, from nestlings less than 13 centimeters (5 in.) long, to very old adults reaching nearly 2 meters (6.5 ft.) in length.^[6]

Remains of this dinosaur were first discovered on the third American Museum of Natural History expedition to the Gobi Desert of Mongolia in 1922. The type specimen was discovered by one the expedition's drivers. This same expedition turned up the remains of many other famous Mongolian dinosaurs, including Protoceratops, Oviraptor, and Velociraptor.^[7] 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. 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 million years ago.

Skulls of P. mongoliensis are flat on top, especially over the back of the skull, with a triangular fossa, or depression, on the outside surface of the maxilla (an upper jaw bone). P. mongoliensis is the largest known species. The skull of the type specimen is 15.2 centimeters (6 in.) long, and the associated femur is 16.2 centimeters (6.4 in.) in length.^[8] The largest documented femora are 21 centimeters (8.25 in.) long.^[9]

[edit] Protiguanodon mongoliense

When describing Psittacosaurus mongoliensis in 1923, Osborn also gave the name Protiguanodon mongoliense to another skeleton found nearby, believing it to represent an ancestor of the ornithopod Iguanodon.^[4] When the skeleton was prepared further, it became clear that it was far more similar to Psittacosaurus.^[8] In 1958, Chinese paleontologist Yang Zhongjian (better known as C.C. Young) renamed the skeleton Psittacosaurus protiguanodonensis, but it is now believed to belong to Psittacosaurus mongoliensis.^[10]

[edit] Psittacosaurus protiguanodonensis

See Protiguanodon mongoliense.

[edit] Psittacosaurus osborni

In 1931, C.C. Young named a new species of Psittacosaurus for a partial skull discovered in Inner Mongolia, China.^[11] The skull was named P. osborni after Henry Fairfield Osborn. These species was later found to be a junior synonym of P. mongoliensis, which is found in nearby strata of the same age.^[12]

[edit] Psittacosaurus tingi

Young described the species Psittacosaurus tingi, based on skull fragments, in the same 1931 report which contained P. osborni.^[11] He later synonymized the two species under the name P. osborni^[10]. Both species are now considered junior synonyms of P. mongoliensis.^[12]

[edit] Psittacosaurus sinensis

A new species of Psittacosaurus was found in the Aptian-Albian Qingshan Formation of Shandong Province, southeast of Beijing, China. Because it had only been found in China, it was called P. sinensis to differentiate it from P. mongoliensis, which had originally been found in Mongolia.^[10] Fossils of more than twenty individuals have since been recovered, including several complete skulls and skeletons, making this the most completely known species after P. mongoliensis.^[5]

P. sinensis is readily distinguished from all others by numerous features of the skull. Adult skulls are smaller than P. mongoliensis and have less teeth. Uniquely, the premaxillary bone contacts the jugal (cheek) bone on the outside of the skull. The jugals flare out sideways, forming "horns" proportionally wider than in any other known Psittacosaurus species. A very small horn is also present at the contact of the jugal and postorbital bone, behind the eye. The mandible (lower jaw) also lacks the fenestra, or hollow opening, seen in other species, and the entire lower jaw is bowed outwards, giving the animal the appearance of an underbite.^[1][12] The skull of an adult P. sinensis is 11.5 centimeters (4.5 inches) long.^[13]

[edit] Psittacosaurus youngi

Chinese paleontologist Zhao Xijin named a new species after his mentor, C.C. Young, in 1962.^[14] However, the single partial skeleton and skull of P. youngi was discovered in the same rocks as P. sinensis and shows a very similar morphology. P. youngi is generally considered a junior synonym of the better known P. sinensis.^[12]

[edit] Psittacosaurus guyangensis

The front half of a skull from Guyang County in the Inner Mongolian Autonomous Region of China was described as P. guyangensis in 1983.^[15] 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 so is usually considered a junior synonym.^[12]

[edit] Psittacosaurus meileyingensis

In 1988, Paul Sereno, Zhao Xijin, and two Chinese colleagues described P. meileyingensis from the Jiufotang Formation, near the town of Meileyingzi, Liaoning Province, northeastern China. The Jiufotang has not been precisely dated, but directly overlies the famous Yixian Formation of the Barremian stage, so a date with the Aptian-Albian stages is likely. This species is known from four fossil skulls, one associated with some skeletal material.^[16]

P. meileyingensis has the shortest snout of any species, and the skull is nearly circular in profile. The orbit (eye socket) is roughly triangular in shape, and the dentary bone of the lower jaw exhibits a bony flange, or projection, on its bottom edge, similar to P. mongoliensis.^[1] The very complete type skull, probably an adult, is approximately 13 centimeters (5.1 in.) long.^[16]

[edit] Psittacosaurus xinjiangensis

Also in 1988, Sereno and Zhao named another new species of Psittacosaurus. P. xinjiangensis is named after the Xinjiang Autonomous Region in which it was discovered.^[17] Several individuals of different ages were discovered and described originally, although the most complete skeleton was that of a juvenile. This was named the type specimen of the species. An adult skeleton was later discovered at a different locality in Xinjiang.^[3] Both of these specimens come from the upper part of the Tugulu Group, which is regarded as Aptian-Albian in age.

This species can be distinguished from others by the jugal "horn," which is flattened on the front end, as well as some features of the teeth. The ilium, one of the three bones of the pelvis, also bears a characteristically long bony process behind the acetabulum (hip socket).^[1] An adult femur has a published length of about 16 centimeters (6.3 in.), similar in size to the type specimen of P. mongoliensis.^[3]

[edit] Psittacosaurus sattayaraki

French paleontologist Eric Buffetaut and his 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.^[18] Most other workers have doubted the validity of this species, and it is generally regarded as a nomen dubium which cannot definitely be referred to Psittacosaurus.^[19][5] However, the original authors continue to defend it as a valid species.^[20]

The dentary of P. sattayaraki may have a flange similar to that found in P. mongoliensis and P. meileyingensis, alth1ough much less prominent.^[18]

[edit] Psittacosaurus neimongolensis

Two new species of Psittacosaurus were described by Dale Russell and Zhao Xijin in 1996. The first is named P. neimongoliensis, after the Mandarin Chinese name for Inner Mongolia. It is based on a nearly complete fossil skeleton, including most of the skull, found in the Early Cretaceous Eijnhoro Formation with seven other individuals.1^[13]

The frontal bone of P. neimongolensis is distinctly narrow compared to that of other species, resulting in a narrower skull overall. The ischium bone of the pelvis is also longer than the femur, which differs from other species in which the ischia and femora are known.^[1] The type specimen has a skull length of 13.2 centimeters (5.2 in.) and a femoral length of 13 centimeters (5.1 in.), but is not fully grown. An adult P. neimongoliensis was probably similar in size to P. mongoliensis.^[13]

[edit] Psittacosaurus ordosensis

Russell and Zhao's other species is named P. ordosensis, after the Ordos prefecture of the Inner Mongolia Autonomous Region, in which it was found. The type specimen is a nearly complete fossil skeleton, including part of the skull. However, only the skull, lower jaw, and foot have been described. Three other specimens were referred to this species.^[13]

P. ordosensis can be distinguished by numerous features of the jugals, which have very prominent "horns."^[1] It is also the smallest known species. One adult skull measures slightly1 less than 11 centimeters in length.^[13]

[edit] Psittacosaurus mazongshanensis

Xu Xing, another Chinese paleontologist, named a new species of Psittacosaurus in 1997, based on a complete skull with associated vertebrae and a forelimb. This material was recovered from the lower sections of the Xinminbao Group (Barremian-Albian), in Gansu Province, near the border with Inner Mongolia. This species is named P. mazongshanensis after the nearby mountain called Mazongshan (Horse Mane Mountain).^[21]

P. mazongshanensis 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. The teeth are also somewhat different from those of other species.^[1]

[edit] Psittacosaurus sibiricus

This species from Russia has been known for decades but is still very obscure. The name P. sibiricus was first published in 2000 in Russian by several Russian scientists, although it has not yet been fully described in English and may or may not actually belong to his species. Several skeletons, at least two nearly complete, are apparently known from the Ilek Formation of Siberia, which may range from the Valanginian to Albian stages of the Early Cretaceous.^[22]

According to a published abstract in English, P. sibiricus is the largest known species of Psittacosaurus. It is also distinguished by its longer neck frill, which is 15 to 18% of the length of the skull. Most species of Psittacosaurus have a very short frill, if any. P. sibiricus also has several horns behind and in front of the eyes. The jugal "horns" are very prominent, and there is a flange on the dentary of the lower jaw, similar to P. mongoliensis and P. meileyingensis.

[edit] Unassigned specimens

Many other specimens either cannot be determined to belong to any particular species, or have not yet been assigned to one. These specimens are generally referred to as Psittacosaurus sp., although in all likelihood they do not belong to a single species, and some may even represent new species.

[edit] References

[edit] External links

• Summary of known ceratop(s)ians on Justin S. Tweet's Thescelosaurus! website.
• A published abstract from the 2004 EAVP conference, which mentions Psittacosaurus remains from Siberia (PDF format).