Editing Protoceratops (section)

==History of discovery==
[[File:Bayanzag.jpg|thumb|300px|[[Flaming Cliffs]] of Mongolia. This highly [[fossil]]iferous locality of the [[Gobi Desert]] yielded the first known remains of ''Protoceratops'']]
In 1900 [[Henry Fairfield Osborn]] suggested that Central Asia may have been the center of origin of most animal species, [[Peking Man#"Out of Asia" theory|including humans]], which caught the attention of explorer and [[zoologist]] [[Roy Chapman Andrews]]. This idea later gave rise to the First (1916 to 1917), Second (1919) and Third (1921 to 1930) Central Asiatic Expeditions to China and [[Mongolia]], organized by the [[American Museum of Natural History]] under the direction of Osborn and field leadership of Andrews. The team of the third expedition arrived in Beijing in 1921 for the final preparations and started working in the field in 1922. During late 1922 the expedition explored the famous [[Flaming Cliffs]] of the Shabarakh Usu region of the [[Djadokhta Formation]], [[Gobi Desert]], now known as the Bayn Dzak region. On 2 September, the photographer [[James B. Shackelford]] discovered a partial juvenile skull—which would become the [[holotype]] specimen (AMNH 6251) of ''Protoceratops''—in reddish [[sandstone]]s. It was subsequently analyzed by the paleontologist [[Walter W. Granger]] who identified it as [[reptilia]]n. On 21 September, the expedition returned to Beijing, and even though it was set up to look for remains of human ancestors, the team collected numerous dinosaur [[fossil]]s and thus provided insights into the rich fossil record of Asia. Back in Beijing, the skull Shackelford had found was sent to the American Museum of Natural History for further study, after which Osborn reached out to Andrews and team via cable, notifying them about the importance of the specimen.<ref name=Granger1923>{{cite journal|last1=Granger|first1=W. W.|last2=Gregory|first2=W. K.|date=1923|title=Protoceratops andrewsi, a pre-ceratopsian dinosaur from Mongolia|journal=American Museum of Natural History Novitates|number=72|page=1−9|hdl=2246/4670|hdl-access=free|url=http://digitallibrary.amnh.org/bitstream/handle/2246/4670//v2/dspace/ingest/pdfSource/nov/N0072.pdf?sequence=1&isAllowed=y}}</ref><ref name=Andrews1932>{{cite book|last1=Andrews|first1=R. C.|year=1932|editor-last1=Reeds|editor-first1=C. A.|title=The New Conquest of Central Asia: a Narrative of the Explorations of the Central Asiatic Expeditions in Mongolia and China, 1921–1930|edition=1st|volume=1|publisher=American Museum of Natural History|location=New York|pages=1–549|oclc=766770|url=https://ia800207.us.archive.org/30/items/newconquestofcen00andr/newconquestofcen00andr.pdf}}</ref>

In 1923 the expedition again prospected the Flaming Cliffs, this time discovering even more specimens of ''Protoceratops'' and also the first remains of ''[[Oviraptor]]'', ''[[Saurornithoides]]'' and ''[[Velociraptor]]''. Most notably, the team discovered the first fossilized dinosaur [[egg]]s near the holotype of ''Oviraptor'' and given how abundant ''Protoceratops'' was, the nest was attributed to this [[taxon]].<ref name=Andrews1932/> This would later result in the interpretation of ''Oviraptor'' as an [[Egg predation|egg-thief]].<ref name=Osborn1924>{{cite journal|last1=Osborn|first1=H. F.|date=1924|title=Three new Theropoda, Protoceratops zone, central Mongolia|journal=American Museum Novitates|number=144|pages=1–12|hdl=2246/3223|hdl-access=free|oclc=40272928|url=http://digitallibrary.amnh.org/bitstream/handle/2246/3223//v2/dspace/ingest/pdfSource/nov/N0144.pdf?sequence=1&isAllowed=y}}</ref> In the same year, Granger and William K. Gregory formally described the new genus and species ''Protoceratops andrewsi'' based on the holotype skull. The [[Specific name (zoology)|specific name]], ''andrewsi'', is in honor of Andrews for his prominent leadership during the expeditions. They identified ''Protoceratops'' as an [[ornithischia]]n dinosaur closely related to ceratopsians representing a possible common ancestor between [[ankylosaur]]s and [[ceratopsia]]ns. Since ''Protoceratops'' was more primitive than any other known ceratopsian at that time, Granger and Gregory coined the new family [[Protoceratopsidae]], mostly characterized by the lack of horns. The co-authors also agreed with Osborn that Asia, if more thoroughly explored, could solve many major evolutionary gaps in the fossil record.<ref name=Granger1923/> Although not stated in the original description, the [[Genus#Use|generic name]], ''Protoceratops'', is intended to mean "first horned face" as it was believed that ''Protoceratops'' represented an early ancestor of [[ceratopsid]]s.<ref>{{cite journal|last1=Gregory|first1=W. K.|date=1927|title=Gaps in the Mongolian Life Record|journal=The Scientific Monthly|volume=24|issue=2|pages=169–181|jstor=7818|bibcode=1927SciMo..24..169G }}</ref> Other researchers immediately noted the importance of the ''Protoceratops'' finds, and the genus was hailed as the "long-sought ancestor of ''Triceratops''". Most fossils were in an excellent state of preservation with even [[sclerotic ring]]s (delicate ocular bones) preserved in some specimens, quickly making ''Protoceratops'' one of the best-known dinosaurs from Asia.<ref name=Andrews1932/><ref name=Brown1940>{{cite journal|last1=Brown|first1=B.|last2=Schlaikjer|first2=E. M.|date=1940|title=The Structure and Relationships of Protoceratops|journal=Annals of the New York Academy of Sciences|volume=40|number=3|pages=133–266|bibcode=1940NYASA..40..133B|doi=10.1111/j.2164-0947.1940.tb00068.x|oclc=1673730|url=https://drive.google.com/file/d/1EM9A8LG5eqbQ5_Ho16QJx0_MebAqLjLQ/view|url-access=subscription}}</ref>
[[File:Protoceratops andrewsi AMNH 6251.jpg|thumb|left|Holotype skull of ''P. andrewsi'', collected during the Third Central Asiatic Expedition]]
After spending much of 1924 making plans for the next fieldwork seasons, in 1925 Andrews and team explored the Flaming Cliffs yet again. During this year more eggs and nests were collected, alongside well-preserved and complete specimens of ''Protoceratops''. By this time, ''Protoceratops'' had become one of the most abundant dinosaurs of the region with more than 100 specimens known, including skulls and skeletons of multiple individuals at different growth stages. Though more remains of ''Protoceratops'' were collected in later years of the expeditions, they were most abundant in the 1922 to 1925 seasons.<ref name=Andrews1932/><ref name=Brown1940/> Gregory and [[Charles C. Mook]] published another description of ''Protoceratops'' in 1925, discussing its anatomy and relationships. Thanks to the large collection of skulls found in the expeditions, they concluded that ''Protoceratops'' represented a ceratopsian more primitive than ceratopsids and not an ankylosaur-ceratopsian ancestor.<ref name=Greggory1925>{{cite journal|last1=Gregory|first1=W. K.|last2=Mook|first2=C. C.|date=1925|title=On Protoceratops, a primitive ceratopsian dinosaur from the Lower Cretaceous of Mongolia|journal=American Museum Novitates|number=156|pages=1–10|hdl=2246/4515|hdl-access=free|url=http://digitallibrary.amnh.org/bitstream/handle/2246/4515//v2/dspace/ingest/pdfSource/nov/N0156.pdf?sequence=1&isAllowed=y}}</ref> In 1940, [[Barnum Brown]] and [[Erich Maren Schlaikjer]] described the anatomy of ''P. andrewsi'' in extensive detail using newly prepared specimens from the Asiatic expeditions.<ref name=Brown1940/>

In 1963, the Mongolian paleontologist [[Demberelyin Dashzeveg]] reported the discovery of a new fossiliferous locality of the Djadokhta Formation: Tugriken Shireh. Like the neighbouring Bayn Dzak, this new locality contained an abundance of ''Protoceratops'' fossils.<ref>{{cite journal|last1=Dashzeveg|first1=D.|date=1963|title=Яйца динозавров|trans-title=Dinosaur eggs|journal=Priroda|volume=9|pages=100|language=ru}}</ref> During the 1960s to 1970s, Polish-Mongolian and Russian-Mongolian paleontological expeditions collected new, partial to complete specimens of ''Protoceratops'' at this locality, making this dinosaur species a common occurrence in Tugriken Shireh.<ref name=Jaworowska1972/><ref name=Mary1975/><ref>{{cite book|last1=Kurochkin|first1=E. N.|last2=Barsbold|first2=R.|date=2000|chapter=The Russian-Mongolian expeditions and research in vertebrate palaeontology|chapter-url=https://artscimedia.case.edu/wp-content/uploads/sites/108/2017/05/17211722/13.-Kurochkin_Barsbold-Russian-Mongolian-expeditions.pdf|editor-last1=Benton|editor-first1=M. J.|editor-last2=Shishkin|editor-first2=M. A.|editor-last3=Unwin|editor-first3=D. M.|editor-last4=Kurochkin|editor-first4=E. N.|title=The Age of Dinosaurs in Russia and Mongolia|publisher=Cambridge University Press|page=235−255}}</ref> Since its discovery, the Tugriken Shireh locality has yielded some of the most significant specimens of ''Protoceratops'', such as the [[Fighting Dinosaurs]],<ref name=Jaworowska1972/> ''[[in situ]]'' individuals—a preservation condition also known as "standing" individuals or specimens in some cases—,<ref name=Jerzykiewiczz1993>{{cite journal|last1=Jerzykiewicz|first1=T.|last2=Currie|first2=P. J.|last3=Eberth|first3=D. A.|last4=Johnston|first4=P. A.|last5=Koster|first5=E. H.|last6=Zheng|first6=J.-J.|date=1993|title=Djadokhta Formation correlative strata in Chinese Inner Mongolia: an overview of the stratigraphy, sedimentary geology, and paleontology and comparisons with the type locality in the pre-Altai Gobi|journal=Canadian Journal of Earth Sciences|volume=30|number=10|pages=2180–2195|bibcode=1993CaJES..30.2180J|doi=10.1139/e93-190|url=https://www.researchgate.net/publication/237174446}}</ref> authentic nests,<ref name=Fastovsky2011/> and small herd-like groups.<ref name=Hone2014/> Specimens from this locality are usually found in articulation, suggesting possible mass mortality events.<ref name=Jerzykiewiczz1993/>

[[Stephan N. F. Spiekman]] and colleagues reported a partial ''P. andrewsi'' skull (RGM 818207) in the collections of the [[Naturalis Biodiversity Center]], [[Netherlands]] in 2015. Since ''Protoceratops'' fossils are only found in the Gobi Desert of Mongolia and this specimen was likely discovered during the Central Asiatic Expeditions, the team concluded that this skull was probably acquired by [[Delft University]] between 1940 and 1972 as part of a collection transfer.<ref>{{cite conference|last1=Spiekman|first1=S. N. F.|last2=Bastiaans|first2=D.|last3=Schulp|first3=A. S.|date=2015|title=A partial skull of Protoceratops andrewsi from the Central Asiatic Expeditions in the Naturalis collections (Leiden, the Netherlands)|conference=European Association of Vertebrate Palaeontologists|url=https://www.researchgate.net/publication/280101760}}</ref>

===Species and synonyms===
[[File:Protoceratops hellenikorhinus holotype skull.jpg|thumb|Holotype skull of ''P. hellenikorhinus'' at the [[Inner Mongolia Museum]]]]
Protoceratopsid remains were recovered in the 1970s from the Khulsan locality of the [[Barun Goyot Formation]], Mongolia, during the work of several Polish-Mongolian paleontological expeditions. In 1975, Polish paleontologists [[Teresa Maryańska]] and [[Halszka Osmólska]] described a second species of ''Protoceratops'' which they named ''P. kozlowskii''. This new species was based on the Khulsan material, mostly consisting of juvenile skull specimens. The specific name, ''kozlowskii'', is in tribute to the Polish paleontologist [[Roman Kozłowski]]. They also named the new genus and species of protoceratopsid ''[[Bagaceratops rozhdestvenskyi]]'', known from specimens of the nearby Hermiin Tsav locality.<ref name=Mary1975>{{cite journal|last1=Maryańska|first1=T.|last2=Osmólska|first2=H.|date=1975|title=Protoceratopsidae (Dinosauria) of Asia|journal=Palaeontologia Polonica|volume=33|page=134−143|url=http://palaeontologia.pan.pl/Archive/1975-33_133-181_36-50.pdf|access-date=10 June 2022|archive-date=21 September 2018|archive-url=https://web.archive.org/web/20180921083509/http://palaeontologia.pan.pl/Archive/1975-33_133-181_36-50.pdf|url-status=dead}}</ref> In 1990 the Russian paleontologist [[Sergei Mikhailovich Kurzanov]] referred additional material from Hermiin Tsav to ''P. kozlowskii''. However, he noted that there were enough differences between ''P. andrewsi'' and ''P. kozlowskii'', and erected the new genus and combination ''[[Breviceratops kozlowskii]]''.<ref>{{cite journal |last1=Kurzanov|first1=S. M.|date=1990|title=Новый род протоцератопсид из позднего мела Монголии|trans-title=A new Late Cretaceous protoceratopsid genus from Mongolia|journal=Paleontological Journal|number=4|pages=91–97|language=ru|url=https://www.geokniga.org/bookfiles/geokniga-paleontologicaljournal1990-4.pdf}}</ref> Though ''Breviceratops'' has been regarded as a [[synonym]] and juvenile stage of ''Bagaceratops'',<ref name=Sereno2000>{{cite book|last1=Sereno|first1=P. C.|date=2000|chapter=The fossil record, systematics and evolution of pachycephalosaurs and ceratopsians from Asia|chapter-url=https://d3qi0qp55mx5f5.cloudfront.net/paulsereno/i/docs/00-Marginocephalia.pdf|editor-last1=Benton|editor-first1=M. J.|editor-last2=Shishkin|editor-first2=M. A.|editor-last3=Unwin|editor-first3=D. M.|editor-last4=Kurochkin|editor-first4=E. N.|title=The Age of Dinosaurs in Russia and Mongolia|publisher=Cambridge University Press|page=489−492}}</ref><ref>{{cite book|last1=Makovicky|first1=P. J.|year=2001|chapter=A Montanoceratops cerorhynchus (Dinosauria: Ceratopsia) Braincase from the Horseshoe Canyon Formation of Alberta|chapter-url=https://archive.org/details/mesozoicvertebra0000unse/page/242/mode/2up?q=montanoceratops|editor-last1=Tanke|editor-first1=D. H.|editor-last2=Carpenter|editor-first2=K.|title=Mesozoic Vertebrate Life|series=Life of the Past|publisher=Indiana University Press|pages=243–262|isbn=978-0-253-33907-2}}</ref> [[Łukasz Czepiński]] in 2019 concluded that the former has enough anatomical differences to be considered as a separate [[taxon]].<ref name=Czepiński19>{{cite journal|last1=Czepiński|first1=Ł.|date=2019|title=Ontogeny and variation of a protoceratopsid dinosaur Bagaceratops rozhdestvenskyi from the Late Cretaceous of the Gobi Desert|journal=Historical Biology|volume=32|issue=10|pages=1394–1421|doi=10.1080/08912963.2019.1593404|bibcode=2020HBio...32.1394C |s2cid=132780322|url=http://dinosaurmailinglist.cmnh.org/2019Apr/pdfzmfpMk1aO4.pdf|access-date=10 June 2022|archive-date=8 July 2021|archive-url=https://web.archive.org/web/20210708144840/http://dinosaurmailinglist.cmnh.org/2019Apr/pdfzmfpMk1aO4.pdf|url-status=dead}}</ref>

In 2001 [[Oliver Lambert (paleontologist)|Oliver Lambert]] with colleagues named a new and distinct species of ''Protoceratops'', ''P. hellenikorhinus''. The first known remains of ''P. hellenikorhinus'' were collected from the Bayan Mandahu locality of the [[Bayan Mandahu Formation]], Inner Mongolia, in 1995 and 1996 during [[China|Sino]]-Belgian paleontological expeditions. The holotype (IMM 95BM1/1) and [[paratype]] (IMM 96BM1/4) specimens consist of large skulls lacking body remains. The holotype skull was found facing upwards, a pose that has been reported in ''Protoceratops'' specimens from Tugriken Shireh. The specific name, ''hellenikorhinus'', is derived from [[Greek language|Greek]] hellenikos (meaning Greek) and rhis (meaning nose) in reference to its broad and angular snout, which is reminiscent of the straight profiles of [[Ancient Greek sculpture|Greek sculptures]].<ref name=Helleniko2001>{{cite journal|last1=Lambert|first1=O.|last2=Godefroit|first2=P.|last3=Li|first3=H.|last4=Shang|first4=C.-Y.|last5=Dong|first5=Z.|date=2001|title=A new Species of Protoceratops (Dinosauria, Neoceratopsia) from the Late Cretaceous of Inner Mongolia (P. R. China)|journal=Bulletin de l'Institut Royal des Sciences Naturelles de Belgique, Sciences de la Terre|volume=71|pages=5–28|url=http://biblio.naturalsciences.be/rbins-publications/bulletin-of-the-royal-belgian-institute-of-natural-sciences-earth-sciences/71-sup-2001/irscnb_p4087_01ec08x_71-sup_bulletin-1.pdf}}</ref> In 2017 abundant protoceratopsid material was reported from [[Alxa League|Alxa]] near Bayan Mandahu,<ref>{{cite journal|last1=Ji|first1=S.|last2=Zhang|first2=L.|last3=Lu|first3=L.|last4=Hao|first14=J.|date=2017|title=The First Discovery of the Late Cretaceous Protoceratopsid Fauna from Alxa, Inner Mongolia, China|journal=Acta Geologica Sinica (English Edition)|volume=91|issue=5|pages=1908–1909|doi=10.1111/1755-6724.13421|bibcode=2017AcGlS..91.1908J |s2cid=134276217 |url=http://www.geojournals.cn/dzxbcn/ch/reader/create_pdf.aspx?file_no=2017endzxb05027&year_id=2017&quarter_id=5&falg=1|url-access=subscription}}</ref> and it may be preferable to ''P. hellenikorhinus''.<ref name=Czepiński19/>

[[Viktor Tereshchenko]] and [[Vladimir R. Alifanov]] in 2003 named a new protoceratopsid dinosaur from the Bayn Dzak locality, ''Bainoceratops efremovi ''. This genus was based on a few dorsal (back) vertebrae that were stated to differ from those of ''Protoceratops''.<ref>{{cite journal|last1=Tereshchenko|first1=V.|last2=Alifanov|first2=V. R.|date=2003|title=Bainoceratops efremovi, a New Protoceratopid Dinosaur (Protoceratopidae, Neoceratopsia) from the Bain-Dzak Locality (South Mongolia)|journal=Paleontological Journal|volume=37|issue=3|pages=293–302|url=https://www.researchgate.net/publication/288557787}}</ref> In 2006 North American paleontologists [[Peter Makovicky]] and [[Mark A. Norell]] suggested that ''Bainoceratops'' may be synonymous with ''Protoceratops'' as most of the traits used to separate the former from the latter have been reported from other ceratopsians including ''Protoceratops'' itself, and they are more likely to fall within the wide intraspecific variation range of the concurring ''P. andrewsi''.<ref name=Makovicky2006>{{cite journal|last1=Makovicky|first1=P. J.|last2=Norell|first2=M. A.|date=2006|title=Yamaceratops dorngobiensis, a New Primitive Ceratopsian (Dinosauria: Ornithischia) from the Cretaceous of Mongolia|journal=American Museum Novitates|number=3530|pages=1–42|doi=10.1206/0003-0082(2006)3530[1:YDANPC]2.0.CO;2|hdl=2246/5808|hdl-access=free|url=https://digitallibrary.amnh.org/bitstream/handle/2246/5808//v2/dspace/ingest/pdfSource/nov/N3530.pdf?sequence=1&isAllowed=y}}</ref> The authors [[Brenda J. Chinnery]] and [[Jhon R. Horner]] in 2007 during their description of ''[[Cerasinops]]'' stated that ''Bainoceratops'', along with other dubious genera, was determined to be either a variant or immature specimen of other genera. Based on this reasoning, they excluded ''Bainoceratops'' from their phylogenetic analysis.<ref>{{cite journal|last1=Chinnery|first1=B. J.|last2=Horner|first2=J. R.|date=2007|title=A new neoceratopsian dinosaur linking North American and Asian taxa|journal=Journal of Vertebrate Paleontology|volume=27|issue=3|pages=625–641|doi=10.1671/0272-4634(2007)27[625:ANNDLN]2.0.CO;2|s2cid=86091277 |url=https://www.academia.edu/24240715}}</ref>

===Eggs and nests===

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|image1 = Nesting Protoceratops.jpg
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|footer = Life restoration from 1927 and model of ''Protoceratops'' eggs based on the ''Oviraptor'' [[nest]] AMNH 6508. This nest was originally thought to represent ''Protoceratops'' eggs
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As part of the Third Central Asiatic Expedition of 1923, Andrews and team discovered the holotype specimen of ''[[Oviraptor]]'' in association with some of the first known fossilized dinosaur eggs (nest AMNH 6508), in the Djadokhta Formation. Each egg was elongated and hard-shelled, and due to the proximity and high abundance of ''Protoceratops'' in the [[Geological formation|formation]], these eggs were believed at the time to belong to this dinosaur. This resulted in the interpretation of the contemporary ''Oviraptor'' as an egg predatory animal, an interpretation also reflected in its generic name.<ref>{{cite journal|last1=Osborn|first1=H. F.|date=1924|title=The discovery of an unknown continent|journal=Natural History|volume=24|issue=2|pages=133–149}}</ref><ref name=Osborn1924/> In [[1975 in paleontology|1975]], the Chinese paleontologist [[Zhao Zikui]] named the new [[oogenera]] ''[[Elongatoolithus]]'' and ''[[Macroolithus]]'', including them in a new [[oofamily]]: the [[Elongatoolithidae]]. As the name implies, they represent elongated dinosaur eggs, including some of referred ones to ''Protoceratops''.<ref>{{cite journal |last1=Zhao|first1=Z. K.|date=1975|title=The microstructures of the dinosaurian eggshells of Nanxiong Basin, Guandong province. On the classification of dinosaur eggs|journal=Vertebrata PalAsiatica|volume=13|issue=2|pages=105–117|language=Chinese|url=http://www.ivpp.cas.cn/cbw/gjzdwxb/xbwzxz/200905/W020090813377364004471.pdf}}</ref>

In 1994 the Russian paleontologist Konstantin E. Mikhailov named the new oogenus ''[[Protoceratopsidovum]]'' from the [[Barun Goyot Formation|Barun Goyot]] and Djadokhta formations, with the type species ''P. sincerum'' and additional ''P. fluxuosum'' and ''P. minimum''. This [[ootaxon]] was firmly stated as belonging to protoceratopsid dinosaurs since they were the predominant dinosaurs where the eggs were found and some skeletons of ''Protoceratops'' were found in close proximity to ''Protoceratopsidovum'' eggs. More specifically, Mikhailov stated that ''P. sincerum'' and ''P. minimum'' were laid by ''Protoceratops'', and ''P. fluxuosum'' by ''Breviceratops''.<ref>{{cite journal|last1=Mikhailov|first1=K. E.|date=1994|title=Theropod and protoceratopsian dinosaur eggs from the Cretaceous of Mongolia and Kazakhstan|journal=Paleontological Journal|volume=28|issue=2|pages=101–120|url=https://www.researchgate.net/publication/285873142}}</ref>
[[File:Citipatibcn4.JPG|thumb|Oviraptorid embryo MPC-D 100/971, a specimen that shed light on the identity of elongatoolithid eggs]]
However, also during 1994, Norell and colleagues reported and briefly described a fossilized [[theropod]] [[embryo]] inside an egg (MPC-D 100/971) from the Djadokhta Formation. They identified this embryo as an [[oviraptorid]] dinosaur and the eggshell, upon close examination, turned out be that of elongatoolithid eggs and thereby the oofamily Elongatoolithidae was concluded to represent the eggs of oviraptorids. This find proved that the nest AMNH 6508 belonged to ''Oviraptor'' and rather than an egg-thief, the holotype was actually a mature individual that perished brooding the eggs.<ref name=Norell1994>{{cite journal|last1=Norell|first1=M. A.|last2=Clark|first2=J. M.|last3=Dashzeveg|first3=D.|last4=Barsbold|first4=R.|last5=Chiappe|first5=L. M.|last6=Davidson|first6=A. R.|last7=McKenna|first7=M. C.|last8=Altangerel|first8=P.|last9=Novacek|first9=M. J.|date=1994|title=A theropod dinosaur embryo and the affinities of the Flaming Cliffs Dinosaur eggs|journal=Science|volume=266|issue=5186|pages=779–782|bibcode=1994Sci...266..779N|doi=10.1126/science.266.5186.779|pmid=17730398|jstor=2885545|s2cid=22333224 |url=https://www.researchgate.net/publication/6110932}}</ref> Moreover, [[phylogenetic analyses]] published in 2008 by Darla K. Zelenitsky and François Therrien have shown that ''Protoceratopsidovum'' represents the eggs of a [[maniraptora]]n more derived than oviraptorids and not ''Protoceratops''.<ref>{{cite journal|last1=Zelenitsky|first1=D. K.|last2=Therrien|first2=F.|date=2008|title=Phylogenetic analysis of reproductive traits of maniraptoran theropods and its implications for egg parataxonomy|journal=Palaeontology|volume=51|issue=4|pages=807–816|doi=10.1111/J.1475-4983.2008.00770.x|bibcode=2008Palgy..51..807Z |s2cid=84859809 |doi-access=}}</ref> The description of the eggshell of ''Protoceratopsidovum'' has further confirmed that they in fact belong to a maniraptoran, possibly [[deinonychosaur]] taxon.<ref>{{cite journal|last1=Choi|first1=S.|last2=Barta|first2=D. E.|last3=Moreno-Azanza|first3=M.|last4=Kim|first4=N-H.|last5=Shaw|first5=C. A.|last6=Varricchio|first6=D. J.|date=2022|title=Microstructural description of the maniraptoran egg Protoceratopsidovum|journal=Papers in Palaeontology|volume=8|issue=2|pages=e1430|doi=10.1002/spp2.1430|bibcode=2022PPal....8E1430C |s2cid=248337010 }}</ref>

Nevertheless, in 2011 an authentic nest of ''Protoceratops'' was reported and described by David E. Fastovsky and colleagues. The nest (MPC-D 100/530) containing 15 articulated juveniles was collected from the Tugriken Shireh locality of the Djadokhta Formation during the work of Mongolian-Japanese paleontological expeditions.<ref name=Fastovsky2011/> Gregory M. Erickson and team in 2017 reported an embryo-bearing egg clutch (MPC-D 100/1021) of ''Protoceratops'' from the also fossiliferous Ukhaa Tolgod locality, discovered during paleontological expeditions of the American Museum of Natural History and [[Mongolian Academy of Sciences]]. This clutch comprises at least 12 eggs and embryos with only 6 embryos preserving nearly complete skeletons.<ref name=Erickson2017/> Norell with colleagues in 2020 examined fossilized remains around the eggs of this clutch which indicate a soft-shelled composition.<ref name=Norell2020S/>

===Fighting Dinosaurs===
[[File:'Fighting dinosaurs'Tugrugeen Shireh, Gobi Desert, 1971.jpg|thumb|left|Fossil of the Fighting Dinosaurs as found in the field, 1971]]
The [[Fighting Dinosaurs]] specimen preserves a ''Protoceratops'' (MPC-D 100/512) and ''Velociraptor'' (MPC-D 100/25) fossilized in combat and provides an important window regarding direct evidence of predator-prey behavior in non-avian dinosaurs.<ref name=Jaworowska1972>{{cite journal|last1=Kielan-Jaworowska|first1=Z.|last2=Barsbold|first2=R.|date=1972|title=Narrative of the Polish-Mongolian Palaeontological Expeditions, 1967–1971|journal=Palaeontologia Polonica|volume=27|pages=1–12|url=http://www.palaeontologia.pan.pl/Archive/1972-27_5-13_1-2.pdf}}</ref><ref name=Barsbolld1974/> In the 1960s and early 1970s, many Polish-Mongolian paleontological expeditions were conducted to the Gobi Desert with the objective of fossil findings. In 1971, the expedition explored several localities of the Djadokhta and [[Nemegt Formation|Nemegt]] formations. During fieldwork on 3 August several fossils of ''Protoceratops'' and ''Velociraptor'' were found at the Tugriken Shire locality (Djadokhta Formation) including a block containing one of each. The individuals in this block were identified as a ''P. andrewsi'' and ''V. mongoliensis''. Although the conditions surrounding their burial were not fully understood, it was clear that they died simultaneously in a struggle.<ref name=Jaworowska1972/>

The specimen, nicknamed the "Fighting Dinosaurs", has been examined and studied by numerous researchers and paleontologists, and there are various opinions on how the animals were buried and preserved altogether. Though a drowning scenario has been proposed by Barsbold,<ref name=Barsbolld1974/> such a hypothesis is considered unlikely given the arid paleoenvironments of the Djadokhta Formation. It is generally thought that they were buried alive by a sandstorm or a collapsed [[dune]].<ref name=Osmolska1993/><ref name=Unwin1995/><ref name=Barsbold2016/>

===Skin impressions and footprints===
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|image1 = Protoceratops with possible skin impressions.jpg
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|image2 = Protoceratops footprint.png
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|footer = AMNH 6418 specimen with possible skin impressions (left), and line diagram of footprint associated with specimen ZPAL Mg D-II/3 (right)
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During the Third Central Asiatic Expedition in 1923, a nearly complete ''Protoceratops'' skeleton (specimen AMNH 6418) was collected at the Flaming Cliffs. Unlike other specimens, it was discovered in a rolled-up position with its [[skull]] preserving a thin, hard, and wrinkled layer of [[Matrix (geology)|matrix]] (surrounding [[sediments]]). This specimen was later described in 1940 by Brown and Schlaikjer, who discussed the nature of the matrix portion. They stated that this layer had a very skin-like texture and covered mostly the left side of the skull from the [[snout]] to the [[neck frill]]. Brown and Schlaikjer discarded the idea of possible skin impressions as this skin-like layer was likely a product of the [[Decomposition|decay]] and burial of the individual, making the sediments become highly attached to the skull.<ref name=Brown1940/>

The potential importance of these remains were unrecognized or given attention, and by 2020 the specimen has already been completely prepared losing all traces of this skin-like layer. Some elements were damaged in the process such as the [[Rostrum (anatomy)|rostrum]].<ref name=Green2022>{{cite web|last1=Greenfield|first1=T.|date=2022|title=The lost Protoceratops mummy – Addendum|website=Incertae Sedis|publisher=WordPress|url=https://incertaesedisblog.wordpress.com/2020/04/11/the-lost-protoceratops-mummy/}}</ref> In 2022 Phil R. Bell and colleagues briefly described these potential soft tissues based on the photographs provided by Brown and Schlaikjer, as well as other ceratopsian soft tissues.<ref>{{cite journal|last1=Bell|first1=P. R.|last2=Hendrickx|first2=C.|last3=Pittman|first3=M.|last4=Kaye|first4=T. G.|last5=Mayr|first5=G.|date=2022|title=The exquisitely preserved integument of Psittacosaurus and the scaly skin of ceratopsian dinosaurs|journal=Communications Biology|volume=5|number=809|page=809 |doi=10.1038/s42003-022-03749-3|doi-access=free|pmc=9374759|pmid=35962036}}</ref> However, although the initial perception was that the entire skin-like layer had been removed, photographs shared by Czepiński during the same year have revealed that the right side of the skull remains intact, retaining much of this layer and pending further analysis.<ref name=Green2022/>

Also from the context of the Polish-Mongolian paleontological expeditions, in 1965 an articulated subadult ''Protoceratops'' skeleton (specimen ZPAL Mg D-II/3) was collected from the Bayn Dzak locality of the Djadokhta Formation. In the 2000s during the [[Fossil preparation|preparation]] of the specimen, a fossilized cast of a four-toed [[digitigrade]] footprint was found below the pelvic girdle. This footprint was described in 2012 by Grzegorz Niedźwiedzki and colleagues who considered it to represent one of the first reported finds of a dinosaur footprint in association with an articulated skeleton, and also the first one reported for ''Protoceratops''.<ref name=Nied2012>{{cite journal|last1=Niedźwiedzki|first1=G.|last2=Singer|first2=T.|last3=Gierliński|first3=G. D.|last4=Lockley|first4=M. G.|date=2012|title=A protoceratopsid skeleton with an associated track from the Upper Cretaceous of Mongolia|journal=Cretaceous Research|volume=33|issue=1 |pages=7–10|doi=10.1016/j.cretres.2011.07.001|bibcode=2012CrRes..33....7N |url=https://juraparkbaltow.pl/wp-content/uploads/2018/07/Niedzwiedzki-Singer-Gierlinski-and-Lockley-2011.pdf}}</ref> The limb elements of the skeleton of ZPAL Mg D-II/3 were described in 2019 by paleontologists Justyna Słowiak, Victor S. Tereshchenko and Łucja Fostowicz-Frelik.<ref name=Justyna2019>{{cite journal|last1=Słowiak|first1=J.|last2=Tereshchenko|first2=V. S.|last3=Fostowicz-Frelik|first3=Ł.|date=2019|title=Appendicular skeleton of Protoceratops andrewsi (Dinosauria, Ornithischia): comparative morphology, ontogenetic changes, and the implications for non-ceratopsid ceratopsian locomotion|journal=PeerJ|volume=7|pages=e7324|doi=10.7717/peerj.7324|doi-access=free|pmc=6657679|pmid=31367485}}</ref> Tereshchenko in 2021 fully described the axial skeleton of this specimen.<ref>{{cite journal|last1=Tereshchenko|first1=V. S.|date=2021|title=Axial Skeleton of Subadult Protoceratops andrewsi from Djadokhta Formation (Upper Cretaceous, Mongolia)|journal=Paleontological Journal|volume=55|issue=7|pages=1408–1457|doi=10.1134/S0031030121120030|bibcode=2021PalJ...55.1408T |s2cid=247387644 }}</ref>