Protoceratops andrewsi

Protoceratops andrewsi was a small, stout neoceratopsian that lived in the Djadokhta dune fields of Late Cretaceous Mongolia. Its skull combined a deep beak, a modest nasal boss and a broad fenestrated frill, but lacked the long horns of later ceratopsids. Numerous skulls from small juveniles to large adults document dramatic growth: the snout deepened and the frill expanded disproportionately as the animal matured. The skeleton indicates mainly quadrupedal locomotion, with some capacity to rear. Exceptional fossils add rare behavioural context. Fifteen juveniles were preserved together in a bowl-shaped nest, and another individual died entangled with Velociraptor mongoliensis. Neither occurrence tells a complete life story, but together they make P. andrewsi one of the most behaviourally informative non-ceratopsid ceratopsians.

Its fossils occur between approximately 75 and 71 million years ago. Values shown here are approximate and reflect the current curated seed dataset.

A narrow, down-curved rostral bone supported a keratinous beak at the front of the upper jaw, opposed by the predentary beak below. Behind it, closely packed cheek teeth formed slicing surfaces for vegetation. The skull broadened toward a parietal-squamosal frill pierced by two large openings that reduced its weight. Adults developed a low nasal boss rather than a long horn and prominent jugal projections at the cheeks. The neck and trunk were robust, the forelimbs weight-bearing and the hind limbs longer and more powerful. Mature shoulder, elbow and forearm anatomy is consistent with habitual quadrupedalism, while some retained features may have allowed occasional rearing on the hind legs.

• Deep skull with a narrow, down-curved rostral beak core
• Broad parietal-squamosal frill pierced by paired openings
• Low nasal boss rather than a long facial horn
• Prominent jugal projections on the cheeks
• Closely packed cheek teeth forming plant-slicing wear surfaces
• Robust shoulder and forelimb anatomy adapted for weight bearing
• Longer hind limbs retaining some capacity for rearing
• Frill size and shape changing strongly through growth

James Blaine Shackelford found the partial juvenile skull AMNH 6251 during the American Museum’s 1922 Central Asiatic Expedition in Mongolia. Walter W. Granger and William King Gregory named Protoceratops andrewsi in 1923, honouring expedition leader Roy Chapman Andrews. The following expeditions recovered many additional skulls and skeletons at the Flaming Cliffs, producing an unusually broad growth series. Eggs discovered there in 1923 were assigned to Protoceratops largely because it was the common dinosaur nearby. That attribution collapsed in 1994 when an embryo inside the same egg type proved to be an oviraptorid, a correction now incorporated into the museum’s own account.

Discovery credit: James Blaine Shackelford.

Naming authors: Walter W. Granger, William King Gregory.

Protoceratops lived among the wind-built dunes and sandy interdune areas recorded by the Djadokhta Formation. The climate was arid to semi-arid, but episodic moisture and patches of vegetation supported a diverse small-bodied fauna. Velociraptor, Oviraptor, Saurornithoides and the armored Pinacosaurus occupied the same broad formation, alongside lizards, mammals and other reptiles. Burial in collapsing or rapidly shifting sand helps explain the three-dimensional skeletons, nests and close associations for which the unit is famous, although no single death mechanism explains every specimen.

The beak and cheek-tooth wear establish herbivory, while the deep jaws supplied leverage for cropping and slicing plants. Adult limb anatomy indicates mainly four-legged travel; rearing to feed, display or defend is mechanically possible but is not directly recorded. The ‘Fighting Dinosaurs’ specimen MPC-D 100/25 preserves P. andrewsi locked against Velociraptor mongoliensis, providing exceptional evidence of a direct physical encounter even though the precise sequence of attack, defence and burial remains debated. A separate nest with fifteen similarly sized juveniles shows that young animals remained together after hatching. It is compatible with extended nest use, but without an adult it does not by itself prove parental care. Strong positive growth of the frill is consistent with a visual social or sexual signal, not proof of one exclusive function.

• The holotype AMNH 6251 is a juvenile skull, so the much larger adult head became known only from later expeditions.
• The 1971 ‘Fighting Dinosaurs’ fossil preserves a Velociraptor foot at the Protoceratops throat while the ceratopsian’s beak grips the predator’s forelimb.
• A bowl-shaped nest from Tugriken Shireh contains fifteen articulated juveniles rather than a clutch of eggs.
• The famous Flaming Cliffs eggs were called Protoceratops eggs for decades, but an oviraptorid embryo overturned that identification in 1994.
• Modern morphometric work finds strong growth-related frill change but no clean split into male and female skull shapes.

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1. 01
   The Paleobiology Database

   Open source
2. 02
   The Fighting Dinosaurs: The position of their bodies before and after death

   Rinchen Barsbold · Paleontological Journal · 2016

   Open source
3. 03
   Fighting Dinosaurs

   American Museum of Natural History

   Open source
4. 04
   A Theropod Dinosaur Embryo and the Affinities of the Flaming Cliffs Dinosaur Eggs

   Mark A. Norell, James M. Clark, Demberelyin Dashzeveg and 6 coauthors · Science · 1994

   Open source
5. 05
   Dinosaur Eggs

   American Museum of Natural History

   Open source
6. 06
   Protoceratops andrewsi, a pre-ceratopsian dinosaur from Mongolia

   Walter W. Granger, William King Gregory · American Museum Novitates 72 · 1923

   Open source
7. 07
   A nest of Protoceratops andrewsi (Dinosauria, Ornithischia)

   David E. Fastovsky, David B. Weishampel, Mahito Watabe and 3 coauthors · Journal of Paleontology · 2011

   Open source
8. 08
   Males Resemble Females: Re-Evaluating Sexual Dimorphism in Protoceratops andrewsi (Neoceratopsia, Protoceratopsidae)

   Leonardo Maiorino, Andrew A. Farke, Tassos Kotsakis, Paolo Piras · PLOS ONE · 2015

   Open source
9. 09
   Three-dimensional geometric morphometric analysis of the skull of Protoceratops andrewsi supports a socio-sexual signalling role for the ceratopsian frill

   Andrew Knapp, Robert J. Knell, David W. E. Hone · Proceedings of the Royal Society B · 2021

   Open source
10. 10
    Appendicular skeleton of Protoceratops andrewsi (Dinosauria, Ornithischia): comparative morphology, ontogenetic changes, and the implications for non-ceratopsid ceratopsian locomotion

    Justyna Słowiak, Victor S. Tereshchenko, Łucja Fostowicz-Frelik · PeerJ · 2019

    Open source
11. 11
    Fossil skeleton of Protoceratops andrewsi, AMNH 6416

    American Museum of Natural History Digital Collections

    Open source