Editing Protoceratops (section)

===Tail function===
[[File:Protoceratops tail spines (2).jpg|thumb|left|Elevated neural spines of the caudal (tail) vertebrae of an assigned ''Protoceratops'' specimen]]
Gregory and Mook in 1925 suggested that ''Protoceratops'' was partially [[Aquatic animal|aquatic]] because of its large feet—being larger than the hands—and the very long neural spines found in the caudal (tail) vertebrae.<ref name=Greggory1925/> Brown and Schlaikjer in 1940 indicated that the expansion of the distal (lower) ischial end may reflect a strong ischiocaudalis muscle, which together with the high tail neural spines were used for [[Aquatic locomotion|swimming]].<ref name=Brown1940/> Barsbold in his brief 1974 description of the [[Fighting Dinosaurs]] specimen accepted this hypothesis and suggested that ''Protoceratops'' was amphibious (water-adapted) and had well-developed swimming capacities based on its side to side flattened tail with very high neural spines.<ref name=Barsbolld1974/>

Jack Bowman Bailey in 1997 disagreed with previous aquatic hypotheses and indicated that the high caudal neural spines were instead more reminiscent of bulbous tails of some [[desert]] lizard species (such as ''[[Heloderma]]'' or ''[[Uromastyx]]''), which are related to store fat with [[metabolic water]] in the tail. He considered a swimming adaptation unlikely given the [[arid]] settings of the Djadokhta Formation.<ref>{{cite journal|last1=Bailey|first1=J. B.|date=1997|title=Neural Spine Elongation in Dinosaurs: Sailbacks or Buffalo-Backs?|journal=Journal of Paleontology|volume=71|issue=6|pages=1124–1146|doi=10.1017/S0022336000036076|jstor=1306608|bibcode=1997JPal...71.1124B |s2cid=130861276 |url=https://www.researchgate.net/publication/280721656}}</ref>

In 2008, based on the occurrence of some ''Protoceratops'' specimens in [[fluvial]] (river-deposited) [[sediment]]s from the Djadokhta Formation and {{dinogloss|centrum|heterocoelous}} (vertebral centra that are saddle-shaped at both ends) caudal vertebrae of protoceratopsids, Tereshchenko concluded that the elevated caudal spines are a swimming adaptation. He proposed that protoceratopsids moved through water using their laterally-flattened tails as a [[Webbed foot|paddle]] to aid in swimming. According to Tereschenko, ''[[Bagaceratops]]'' was fully aquatic while ''Protoceratops'' was only partially aquatic.<ref>{{cite journal|last1=Tereschhenko|first1=V. S.|date=2008|title=Adaptive Features of Protoceratopsids (Ornithischia: Neoceratopsia)|journal=Paleontological Journal|volume=42|issue=3|pages=50–64|doi=10.1134/S003103010803009X|bibcode=2008PalJ...42..273T |s2cid=84366476 |url=https://www.researchgate.net/publication/226432157}}</ref> Longrich in 2010 argued that the high tail and frill of ''Protoceratops'' may have helped it to shed excess heat during the day—acting as large-surface structures—when the animal was active in order to survive in the relatively arid environments of the Djadokhta Formation without highly developed [[Cooling down|cooling mechanisms]].<ref name=Longriich20110>{{cite book|last1=Longrich|first1=N. R.|date=2010|chapter=The Function of Large Eyes in Protoceratops: A Nocturnal Ceratopsian?|chapter-url=https://books.google.com/books?id=OWpQW_WhPAsC&pg=PA308|editor1-last=Ryan |editor1-first=M. J.|editor2-last=Chinnery-Allgeier|editor2-first=B. J.|editor3-last=Eberth|editor3-first=D. A.|title=New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium|pages=308–327|publisher=Indiana University Press|isbn=978-0-253-35358-0}}</ref>
[[File:Koreaceratops_NT.jpg|thumb|''Koreaceratops'' restored in a swimming behavior. This hypothesis has not yet reached a consensus]]
In 2011, during the description of ''[[Koreaceratops]]'', Yuong-Nam Lee and colleagues found the above swimming hypotheses hard to prove based on the abundance of ''Protoceratops'' in [[Aeolian processes|eolian]] (wind-deposited) sediments that were deposited in prominent arid environments. They also pointed out that while taxa such as ''[[Leptoceratops]]'' and ''[[Montanoceratops]]'' are recovered from fluvial sediments, they are estimated to be some of the poorest swimmers. Lee and colleagues concluded that even though the tail morphology of ''Koreaceratops''—and other basal ceratopsians—does not argues against swimming habits, the cited evidence for it is insufficient.<ref>{{cite journal|last1=Lee|first1=Y.-N.|last2=Ryan|first2=M. J.|last3=Kobayashi|first3=Y.|date=2011|title=The first ceratopsian dinosaur from South Korea|journal=Naturwissenschaften|volume=98|issue=1|pages=39–49|bibcode=2011NW.....98...39L|doi=10.1007/s00114-010-0739-y|pmid=21085924|s2cid=23743082|url=http://doc.rero.ch/record/31549/files/PAL_E590.pdf}}</ref>

Tereschhenko in 2013 examined the structure of the caudal vertebrae spines of ''Protoceratops'', concluding that it had adaptations for [[Terrestrial animal|terrestrial]] and aquatic habits. Observations made found that the high number of caudal vertebrae may have been useful for swimming and use the tail to counter-balance weight. He also indicated that the anterior caudals were devoid of high neural spines and had increased mobility—a mobility that stars to decrease towards the high neural spines—, which suggest that the tail could be largely raised from its base. It is likely that ''Protoceratops'' raised its tail as a signal ([[Display (zoology)|display]]) or females could use this method during [[Oviparity|egg laying]] to expand and relax the [[cloaca]].<ref name=Tereschhenko20133/>

In 2016, Hone and team indicated that the tail of ''Protoceratops'', particularly the mid region with elevated neural spines, could have been used in display to impress potential mates and/or for species recognition. The tail may have been related with structures like the frill for displaying behavior.<ref name=Hone2016/>

Kim with team in 2019 cited the elongated tail spines as well-suited for swimming. They indicated that both ''Bagaceratops'' and ''Protoceratops'' may have used their tails in a similar fashion during similar situations, such as swimming, given how similar their postcranial skeletons were. The team also suggested that a swimming adaptation could have been useful to avoid aquatic predators, such as [[crocodylomorphs]].<ref name=Kim2019>{{cite journal|last1=Kim|first1=B.|last2=Yun|first2=H.|last3=Lee|first3=Y.-N.|date=2019|title=The postcranial skeleton of Bagaceratops (Ornithischia: Neoceratopsia) from the Baruungoyot Formation (Upper Cretaceous) in Hermiin Tsav of southwestern Gobi, Mongolia|journal=Journal of the Geological Society of Korea|volume=55|number=2|pages=179–190|doi=10.14770/jgsk.2019.55.2.179|s2cid=150321203 |doi-access=|url=http://www.jgsk.or.kr/_common/do.php?a=current&b=21&bidx=1526&aidx=19356#JGSK_2019_v55n2_179_B19|url-access=subscription}}</ref>