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Psittacosaurus

2007 Schools Wikipedia Selection. Related subjects: Dinosaurs

   iPsittacosaurus

                       Fossil range: Early Cretaceous

               Scientific classification

   Kingdom:    Animalia
   Phylum:     Chordata
   Class:      Sauropsida
   Superorder: Dinosauria
   Order:      Ornithischia
   Suborder:   Marginocephalia
   Infraorder: Ceratopsia
   Family:     Psittacosauridae
   Genus:      Psittacosaurus
               Osborn, 1923

                                   Species

     * P. mongoliensis ( type)

        Osborn, 1923
     * P. sinensis

         Young, 1958
     * P. meileyingensis

         Sereno et al., 1988
     * P. xinjiangensis

        Sereno & Zhao, 1988
     * ?P. sattayaraki

         Buffetaut & Suteethorn, 1992
     * P. neimongoliensis

         Russell & Zhao, 1996
     * P. ordosensis

        Russell & Zhao, 1996
     * P. mazongshanensis

         Xu, 1997
     * ?P. sibiricus

         Voronkevich, 1998
     * P. lujiatunensis

         Zhou et al., 2006

                                  Synonyms

   Protiguanodon  Osborn, 1923

   Psittacosaurus ( IPA pronunciation: [,sɪ.tæ.koʊ'soʊr.əs], from the
   Greek for 'parrot lizard') is a genus of psittacosaurid ceratopsian
   dinosaur from the Early Cretaceous Period of what is now Asia, about
   130 to 100 million years ago. It is notable for being the most
   species-rich dinosaur genus. At least eight extinct species are
   recognized from fossils found in different regions of China and
   Mongolia, with possible additional species from Thailand and Russia.

   All species of Psittacosaurus were gazelle-sized bipedal herbivores
   characterized by a high, powerful beak on the upper jaw. At least one
   species had long, quill-like structures on its tail and lower back,
   possibly serving a display function. Psittacosaurs were extremely early
   ceratopsians and, while they developed many novel adaptations of their
   own, they also shared many anatomical features with later ceratopsians,
   such as Protoceratops and the elephant-sized Triceratops.

   Psittacosaurus is not as familiar to the general public as its distant
   relative Triceratops but it is one of the most completely known
   dinosaur genera. Fossils of over 150 individuals have been collected so
   far, including many complete skeletons. Most different age classes are
   represented, from nestling 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
   its use as an index fossil for Early Cretaceous sediments of central
   Asia.

Description

   Different species of Psittacosaurus varied in size and specific
   features of the skull and skeleton, but shared the same overall body
   shape. The best-known species, P. mongoliensis, reached 2  meters
   (6.5 ft) in length. The maximum adult body weight was most likely over
   20  kilograms (44 lb) in P. mongoliensis. Several species approached P.
   mongoliensis in size (P. xinjiangensis, P. neimongoliensis), while
   others were somewhat smaller (P. sinensis, P. meileyingensis). P.
   ordosensis was the smallest known species, 30% smaller than P.
   mongoliensis. The largest was P. lujiatunensis, which was 30% larger
   than P. mongoliensis.
   Breathing, sleeping model of Psittacosaurus sp., in the Natural History
   Museum, London.
   Enlarge
   Breathing, sleeping model of Psittacosaurus sp., in the Natural History
   Museum, London.

   The skull of Psittacosaurus was highly modified compared to other
   ornithischian dinosaurs. The skull was extremely tall and short, with
   an almost round profile in some species. The portion in front of the
   orbit (eye socket) was only 40% of total skull length, shorter than any
   other known ornithischian. Both upper and lower jaws sported a
   pronounced beak, formed from the rostral and predentary bones,
   respectively. The bony core of the beak may have been sheathed in
   keratin to provide a sharp cutting surface for cropping plant material.
   Psittacosaurus skulls shared several adaptations with more derived
   ceratopsians, such as the unique rostral bone at the tip of the upper
   jaw, and the widely flared jugal (cheek) bones. However, there was
   still no sign of the bony neck frill or prominent facial horns which
   would develop in later ceratopsians.

   Psittacosaurus postcranial skeletons were much more typical of a
   "basic" bipedal ornithischian. In P. mongoliensis, similarly to other
   species, the forelimbs were only 58% as long as the hindlimbs,
   indicating that these animals were almost totally bipedal in life.
   There were only four digits on the hand, as opposed to the five fingers
   found in almost all other ornithischians (including more derived
   ceratopsians). Overall, the four-toed hindfoot was very similar to many
   other small ornithischians.

   Like many psittacosaurs, Psittacosaurus had a remarkably deep skull,
   superficially like those of parrots.

Taxonomy

   Psittacosaurus was named in 1923 by Henry Fairfield Osborn,
   paleontologist and president of the American Museum of Natural History
   (AMNH). The generic name is composed of the Greek words ψιττακος
   (psittakos; "parrot") and σαυρος (sauros; "lizard"), suggested by the
   superficially parrot-like beak of these animals and their reptilian
   nature.

Species of Psittacosaurus

   Over a dozen species have been referred to the genus Psittacosaurus,
   although only eight to ten are considered valid today. This is the
   highest number of valid species currently assigned to any single
   dinosaur genus (not including birds). In contrast, most other dinosaur
   genera are monospecific, containing only a single known species. The
   difference is most likely due to quirks of the fossil record. While
   Psittacosaurus is known from dozens 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 analyzed 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 be preserved in the fossil record. Therefore actual species
   diversity may be much higher than currently recognized in this and
   other dinosaur genera.
     * Valid Psittacosaurus species
          + Psittacosaurus mongoliensis — Mongolia, northern China
          + Psittacosaurus sinensis — northeastern China
          + Psittacosaurus meileyingensis — north-central China
          + Psittacosaurus xinjiangensis — northwestern China
          + Psittacosaurus neimongoliensis — north-central China
          + Psittacosaurus ordosensis — north-central China
          + Psittacosaurus mazongshanensis — northwestern China
          + Psittacosaurus lujiatunensis - northeastern China
     * Possible Psittacosaurus species
          + ?Psittacosaurus sattayaraki - Thailand
          + ?Psittacosaurus sibiricus - Russia (southern Siberia)

Classification

   Psittacosaurus is the type genus of the family Psittacosauridae, which
   was also named by Osborn in 1923. Only one other genus,
   Hongshanosaurus, is currently classified in this family alongside
   Psittacosaurus. Psittacosaurids were basal to almost all known
   ceratopsians except Yinlong and perhaps Chaoyangsaurus. While
   Psittacosauridae was an early branch of the ceratopsian family tree,
   Psittacosaurus itself was probably not directly ancestral to any other
   groups of ceratopsians. All other ceratopsians retained the fifth digit
   of the hand, a plesiomorphy or primitive trait, whereas all species of
   Psittacosaurus had only four digits on the hand. 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. It is considered highly unlikely that the fifth digit or
   antorbital fenestra would evolve a second time.

Provenance

   Psittacosaurus is known from over 150 individual specimens, of which
   over 75 belong to the type species, P. mongoliensis. All Psittacosaurus
   fossils discovered so far have been found in Early Cretaceous sediments
   in Asia. The most common age of geologic formations bearing
   Psittacosaurus fossils is Aptian- Albian, or approximately 125 to 100
   million years ago. However, specimens attributed to this genus have
   also been recovered from slightly older strata, such as the Yixian
   Formation, which is considered to date from the Hauterivian through
   Barremian stages of the Early Cretaceous Period, or approximately 136
   to 125 million years ago. The genus may therefore have existed for more
   than 30 million years. Nearly all sedimentary formations of Barremian
   to Albian age in Mongolia and northern China have produced fossils of
   Psittacosaurus, leading to its use as an index fossil for the region.

Paleobiology

   Psittacosaurus is extremely well-known and represented by hundreds of
   specimens, allowing a more detailed analysis of its life history than
   is possible for the vast majority of dinosaurs.

Diet

   Psittacosaurs had self-sharpening teeth that would have been useful for
   cropping and slicing tough plant material. However, unlike later
   ceratopsians, they did not have teeth suitable for grinding or chewing
   their food. Instead, they used gastroliths, stones swallowed to wear
   down food as it passed through the digestive system. Gastroliths,
   sometimes numbering more than fifty, are occasionally found in the
   abdominal cavities of psittacosaurs, and may have been stored in a
   gizzard, as in modern birds.

Integument

   A picture of Psittacosaurus showing the integumentary structures on the
   tail and hips.
   Enlarge
   A picture of Psittacosaurus showing the integumentary structures on the
   tail and hips.

   The integument, or body covering, of Psittacosaurus is known from a
   Chinese specimen, which most likely comes from the Yixian Formation of
   Liaoning. The specimen, which is not yet assigned to any particular
   species, was illegally exported from China, in violation of Chinese
   law, but was purchased by a German museum and arrangements are being
   made to return the specimen to China.

   Most of the body was covered in scales. Larger scales were arranged in
   irregular patterns, with numerous smaller scales occupying the spaces
   between them, similarly to skin impressions known from other
   ceratopsians, such as Chasmosaurus. However, a series of what appear to
   be hollow, tubular bristles, approximately 16 centimeters (6.4 in)
   long, were also preserved, arranged in a row down the dorsal (upper)
   surface of the tail. The structures appear similar to the protofeathers
   found on numerous theropod dinosaurs from the same formation, although
   they may or may not be homologous. As the structures are only found in
   a single row on the tail, it is unlikely that they were used for
   thermoregulation, but they may have been useful for communication
   through some sort of display.

Growth rate

   A Psittacosaurus skeleton.
   Enlarge
   A Psittacosaurus skeleton.

   Several juvenile Psittacosaurus have been found. The smallest is a P.
   mongoliensis hatchling in the AMNH collection, which is only 11 to 13
   centimeters (4-5 in) long, with a skull 2.8 centimeters (1 in) in
   length. Another hatchling skull at the AMNH is only 4.6 centimeters
   (1.8 in) long. Both specimens are from Mongolia. Juveniles discovered
   in the Yixian Formation are approximately the same age as the larger
   AMNH specimen. Adult Psittacosaurus mongoliensis approached 2 meters
   (6.5 ft) in length.

   A histological examination of P. mongoliensis has determined the growth
   rate of these animals. The smallest specimens in the study were
   estimated at three years old and less than 1 kilogram (2.2 lb), while
   the largest were nine years old and weighed almost 20 kilograms
   (44 lb). This indicates relatively rapid growth compared to most
   reptiles and marsupial mammals, but slower than modern birds and
   placental mammals.

Parental Care

   An extremely well-preserved specimen found in the Yixian Formation of
   Liaoning Province, China provides some of the best evidence for
   parental care in dinosaurs. This specimen consists of an adult
   Psittacosaurus (not assigned to any particular species), which is
   closely associated with 34 articulated juvenile skeletons, all
   preserved in three dimensions. The young Psittacosaurus, all
   approximately the same age, are intertwined in a group underneath the
   adult, although all 34 skulls are positioned above the mass of bodies,
   as they would have been in life. This suggests that the animals were
   alive at the time of burial, which must have been extremely rapid,
   perhaps due to the collapse of a burrow.

   The juvenile bones are very small but are well- ossified. This has been
   taken as evidence of extensive parental care, as the young must have
   been in the nest long enough for their bones to become ossified. The
   sheer number of offspring in the nest suggest that they did not all
   belong to the preserved adult, indicating that Psittacosaurus may have
   engaged in some sort of communal nesting, perhaps similar to ostriches.
   However, even very young psittacosaur teeth appear worn, indicating
   they chewed their own food and may have been precocial, although this
   does not rule out continued parental care.

Predation

   Another fossil from the Yixian Formation provides direct evidence of
   Psittacosaurus as a prey animal. One skeleton of Repenomamus
   giganticus, a large, aquatic triconodont mammal, is preserved with the
   remains of a juvenile Psittacosaurus in its abdominal cavity. Several
   of the juvenile's bones are still articulated, indicating that the
   carnivorous mammal swallowed its prey in large chunks. This specimen is
   notable in that it is the first known example of Mesozoic mammals
   preying on live dinosaurs. Heavy predation on juvenile Psittacosaurus
   may have resulted in R-selection, the production of more numerous
   offspring to counteract this loss.

Related Genera

     * Hongshanosaurus
     * Chaoyangsaurus

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