Psittacosaurus mongoliensis

Psittacosaurus mongoliensis was an early member of Ceratopsia, the lineage that later produced Protoceratops and the giant horned dinosaurs. It lacked the long frill and facial horns of those later relatives, but already possessed the group’s distinctive rostral bone at the tip of the upper beak. A short trunk, long hind limbs, much shorter forelimbs and a balancing tail made the adult animal principally bipedal. The name-bearing skeleton AMNH 6254 came from the Öösh locality in Mongolia and remains central to the species. Other referred skeletons preserve growth stages and concentrated masses of rounded stones. The famous Psittacosaurus specimen with skin, countershading and tail bristles belongs to an uncertain species from China and cannot safely supply those features to P. mongoliensis.

Its fossils occur between approximately 110 and 100 million years ago. Values shown here are approximate and reflect the current curated seed dataset.

The skull was high and short, with a strongly curved rostral bone forming the core of a keratin-covered upper beak. Large eye sockets and outwardly expanded jugal bones gave the head a broad, angular outline, but there was no enlarged neck frill. Teeth were confined behind the beak; oblique wear facets show that the jaws processed vegetation rather than merely clipping it. Each hand had four digits, a reduction from the five-fingered condition of many early ornithischians. The hind limbs were substantially longer and more robust than the forelimbs, supporting habitual bipedal locomotion. Several referred P. mongoliensis skeletons contain tightly associated polished stones interpreted as gastroliths, although exactly how much grinding occurred in the gut remains debated.

• Deep, short skull tipped by a strongly curved rostral bone
• Keratinous beak reconstructed over the toothless jaw tips
• Outwardly flared jugal bones forming angular cheek projections
• No enlarged neck frill or long facial horns
• Closely packed cheek teeth with oblique wear surfaces
• Four functional fingers on each hand
• Short forelimbs and substantially longer hind limbs
• Associated concentrations of polished stones interpreted as gastroliths

During the American Museum of Natural History’s 1922 Central Asiatic Expedition, a Mongolian driver recorded as Wong found the ‘Red Mesa skeleton’ at Öösh in the Artsa Bogdo Basin. The specimen, AMNH 6254, includes a skull and much of an articulated skeleton. Henry Fairfield Osborn introduced Psittacosaurus mongoliensis in 1923 and provided a fuller description in 1924. In the same work he named another expedition skeleton Protiguanodon mongoliense; later study placed that animal within Psittacosaurus and generally treated the name as a synonym of P. mongoliensis. Additional Mongolian specimens, including juveniles and histologically sampled long bones, have made the species important for studying early ceratopsian growth.

Discovery credit: Wong (Central Asiatic Expedition driver).

Naming authors: Henry Fairfield Osborn.

The Öösh locality lay in an inland Early Cretaceous basin in what is now southern Mongolia. Its terrestrial sediments preserve an ecosystem much less densely sampled than the younger Gobi dune fields. The available rocks and fauna are compatible with a seasonally dry landscape crossed by local water sources, but the precise mix of dunes, floodplains and vegetated ground is not securely resolved. The formation’s age has also been assigned differently in the literature, so this profile uses a cautious Aptian–Albian interval rather than presenting one exact date as settled.

The beak and worn cheek teeth identify Psittacosaurus mongoliensis as a plant eater capable of cropping and processing relatively tough vegetation. Concentrated stone masses inside referred skeletons are consistent with additional food processing in a muscular gut, but they do not reveal a preferred plant. Adult limb proportions support habitual movement on two legs; the forelimbs could still brace or manipulate objects without making the animal a regular quadruped. Long-bone histology records an S-shaped growth curve and maximum growth faster than living reptiles and marsupials but slower than most birds and placental mammals. No species-specific nest, trackway or mass association demonstrates parental care, herd structure or migration.

• AMNH 6254, the name-bearing skeleton, was found in 1922 and introduced to science the following year.
• The genus name refers to the parrot-like rostral bone at the tip of the upper jaw, not to a close relationship with parrots.
• Its four-fingered hand is an unusual digit reduction among early ornithischian dinosaurs.
• A 2000 histology study produced the first mass-versus-age growth curve reconstructed for a dinosaur.
• The celebrated skin, colour and tail-bristle specimen often used to illustrate Psittacosaurus is not securely P. mongoliensis.

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1. 01
   The Paleobiology Database

   Open source
2. 02
   Two Lower Cretaceous dinosaurs of Mongolia

   Henry Fairfield Osborn · American Museum Novitates 95 · 1923

   Open source
3. 03
   Taxonomy, cranial morphology, and relationships of parrot-beaked dinosaurs (Ceratopsia: Psittacosaurus)

   Paul C. Sereno · New Perspectives on Horned Dinosaurs · 2010

   Open source
4. 04
   Growth curve of Psittacosaurus mongoliensis Osborn (Ceratopsia: Psittacosauridae) inferred from long bone histology

   Gregory M. Erickson, Tatyana A. Tumanova · Zoological Journal of the Linnean Society · 2000

   Open source
5. 05
   Psittacosaurus: Hall of Ornithischian Dinosaurs

   American Museum of Natural History

   Open source
6. 06
   Psittacosaurus mongoliensis skeleton, AMNH 6254, Oshih, Artsa Bogdo Basin

   American Museum of Natural History Digital Collections

   Open source