Protoceratopsidae

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Protoceratopsids
Temporal range:
Ma
↓
Two protoceratopsids: Bagaceratops (top) and Protoceratops (bottom)
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: †Ornithischia
Clade: †Ceratopsia
Parvorder: †
Coronosauria
Family: †Protoceratopsidae
Granger & Gregory, 1923
Type species
†
Protoceratops andrewsi

Granger & Gregory, 1923
Subgroups
Synonyms
  • Bagaceratopidae Alifanov, 2003
  • Bagaceratopsidae Alifanov, 2003 (Ősi et al., 2010)
  • Protoceratopidae Granger & Gregory, 1923 (Tereschenko & Alifanov, 2003)
  • Protoceratopsinae Granger & Gregory, 1923
  • Protoceratopoidea Granger & Gregory, 1923 (Tereschenko, 2007)

Protoceratopsidae is a family of basal (primitive)

ceratopsids
.

Description

Size comparison of four protoceratopsids

Protoceratopsids were relatively small ceratopsians, averaging around 1-2.5 m in length from head to tail.

foramina dotted the maxilla which allowed branches from the trigimenal nerve to reach the tissues attached to the maxilla, indicating that such tissues were likely muscular.[3] The end of the upper jaw was likely not fleshy but instead covered by a horn-like material, and the upper and lower jaws curved in towards each other. Compared to more derived ceratopsians, protoceratopsids had a deep and wide oral cavity, though more narrow than in predecessors like Psittacosaurus, which may have aided in breathing or thermoregulation. In Protoceratopsidae, the nasal cavity, which was ancestrally one large cavity, was split into two by the hard palate. This splitting likely happened to accommodate the deeper oral cavity.[2]

The vertebral column of protoceratopsids was S-shaped, and the vertebrae had unusually long

centrum.[1] The neural spines on the caudal vertebrae were longer in the middle of the tail than at the base, increasing the tail's height and flattening it. The middle of the tail was rigid and straight. The entire tail was quite horizontally flexible, but vertical movement was limited.[4] The neck had limited mobility, especially in the lateral direction. The neck allowed individuals to bend their necks up and down so that they could reach food.[1]

Classification

The family Protoceratopsidae was introduced by

monophyletic, but probably excludes some dinosaurs that have been traditionally thought of as protoceratopsids (for example, Leptoceratops and Montanoceratops).[7] The latter genera are now often classified in a mostly North American family Leptoceratopsidae.[8]

Sereno in 2000 included three genera in Protoceratopsidae: Protoceratops,

Lamaceratops and Breviceratops.[12]

In 2019 Czepiński analyzed a vast majority of referred specimens to the ceratopsians Bagaceratops and Breviceratops, and concluded that most were in fact specimens of the former. Although the genera Gobiceratops, Lamaceratops, Magnirostris, and Platyceratops, were long considered valid and distinct taxa, and sometimes placed within Protoceratopsidae, Czepiński found the diagnostic features used to distinguish these taxa to be largely present in Bagaceratops and thus becoming synonyms of this genus. Under this reasoning, Protoceratopsidae consists of Bagaceratops, Breviceratops, and Protoceratops. Based on cranial characters such as presence or absence of premaxillary teeth and an antorbital fenestra, P. andrewsi is the basal-most protoceratopsid and Bagaceratops the derived-most one. Below are the proposed phylogenetic relationships within Protoceratopsidae by Czepiński:[13]

Protoceratopsidae

Protoceratops andrewsi

Protoceratops hellenikorhinus

Paleobiology

Daily activity

Protoceratops skull with large sclerotic rings

Based on the size of its

sclerotic ring, Protoceratops had an unusually large eye among protoceratopsids. In birds, a medium-sized sclerotic ring indicates that the animal is a predator, a large sclerotic ring indicates that it is nocturnal, and the largest ring size indicates it is a nocturnal predator. Eye size is an important adaptation in predators and nocturnal animals because a larger eye has increased sensitivity and resolution. Because of the energy necessary to maintain a larger eye and the weakness of the skull that corresponds with a larger orbit, Nick Longrich argues that this structure may have been an adaptation for a nocturnal lifestyle. Protoceratops's mouth structures and general abundance indicate it was not a predator, so if it were also diurnal, then it would have been expected to have a much smaller sclerotic ring size. If Protoceratops was nocturnal, it could avoid the hottest parts of the day and survive in an arid environment without highly developed cooling mechanisms.[14]

Sexual Dimorphism

There is no conclusive evidence supporting sexual dimorphism for Protoceratops andrewsi

geometric morphometrics to analyze the dimorphism in Protoceratops andrewsi and concluded that there is no difference in male and female structures.[15] Alternatively, Dodson's analysis of structure sizes in large Protoceratops found that they were dimorphic. The length and width of the frill, parietal fenestra, and external nares, the nasal height, the skull width, the orbit height, and the coronoid process height all varied with sex.[16]

Growth

There are three phases in the life cycle of a protoceratopsid: juvenile, subadult, and adult. Juveniles are roughly one third the size of an adult and have an underdeveloped frill and nasal bump. They have not developed epijugals. Nests containing juveniles have been found indicating that they received some level of parental care.[17] In the subadult stage, individuals are two thirds the size of an adult, and the frill and quadrates grow wider. The epijugal begins forming. As an adult, the frill becomes even larger, the epijugal is fully formed, and a small nasal horn develops.[15]

Social behavior

Protoceratops group of four juveniles buried alive

There is evidence that Protoceratops formed groups. Specimens of juveniles and young adults are often found in groups, although adults tend to be solitary. The nature of these groups is not completely known, though herds of young likely formed for protection from predators, and adults are believed to have come together for communal nesting.[18]

Locomotion

Protoceratopsids were likely slow runners and tended to move at a walk or a trot.[1] Their legs may have been straight, creating an upright posture, but there are some theories that they were splayed out to the side, contributing to their slowness.[19] The skeleton of Protoceratops juveniles indicates that protoceratopsids were able to employ facultative bipedalism when young and became obligate quadrupeds in adulthood. However, adults still had proportions allowing the capacity to occasionally stand on two legs.

Tail function

Tereschenko proposed that protoceratopsids were actually aquatic, using their laterally-flattened tails as a paddle to aid in swimming. According to Tereschenko, Bagaceratops was fully aquatic while Protoceratops was only partially aquatic.[1]

Paleoenvironment

Protoceratopsids likely lived in highly arid regions. Specimens are often found in

sandstones. Because the posture of some animals is preserved, it is likely that they were buried during a sandstorm or a dune collapse.[20][21]

Paleobiogeography

Protoceratopsids have so far been found in rocks from the

Bering Land Bridge into North America between 120Ma and 140Ma. Protoceratopsids are found in Asia but not North America.[14]

See also

References

  1. ^
    S2CID 84366476
    .
  2. ^ a b Osmolska, Halszka (1986). "STRUCTURE OF NASAL AND ORAL CAVITIES IN THE PROTOCERATOPSID DINOSAURS (CERATOPSIA, ORNITHISCHIA)". Paleontologica. 31 (1–2): 145–157.
  3. doi:10.1111/j.1502-3931.1973.tb00873.x
    .
  4. S2CID 84639150
    .
  5. hdl:2246/4670
    .
  6. ^ Maryańska, T.; Osmólska, H. (1975). "Protoceratopsidae (Dinosauria) of Asia" (PDF). Palaeontologia Polonica. 33: 134−143.
  7. doi:10.1127/njgpa/210/1998/41
    .
  8. ISBN 978-0-253-33907-2
    .
  9. ^ Sereno, P. C. (2000). "The fossil record, systematics and evolution of pachycephalosaurs and ceratopsians from Asia" (PDF). In Benton, M. J.; Shishkin, M. A.; Unwin, D. M.; Kurochkin, E. N. (eds.). The Age of Dinosaurs in Russia and Mongolia. Cambridge University Press. p. 489−492.
  10. hdl:2246/5808
    .
  11. S2CID 202867827
    .
  12. ^ Alifanov, V. R. (2003). "Two new dinosaurs of the infraorder Neoceratopsia (Ornithischia) from the Upper Cretaceous of the Nemegt depression, Mongolian People's Republic". Paleontological Journal. 37 (5): 524–534.
  13. S2CID 132780322
    .
  14. ^
    ISBN 978-0-253-35358-0
    .
  15. ^
    PMID 25951329
    .
  16. ISSN 1937-2337
    .
  17. S2CID 129085129
    .
  18. PMID 25426957
    .
  19. ISBN 978-0-521-71902-5
    .
  20. JSTOR 3515294
    .
  21. doi:10.5575/geosoc.116.1.I_II
    .
  22. ^ Holtz, Thomas R. Jr. (2011) Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages, Winter 2010 Appendix.
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