Editing Protoceratops (section)

===Evolution===
[[File:Bagaceratops & Protoceratops evolution.png|thumb|left|Hypothesized transition from ''P. andrewsi'' to ''B. rozhdestvenskyi'']]
Longrich and team in 2010 indicated that highly derived morphology of ''P. hellenikorhinus''—when compared to ''P. andrewsi''—indicates that this species may represent a lineage of ''Protoceratops'' that had a longer evolutionary history compared to ''P. andrewsi'', or simply a direct descendant of ''P. andrewsi''. The difference in morphologies between ''Protoceratops'' also suggests that the nearby [[Bayan Mandahu Formation]] is slightly younger than the Djadokhta Formation.<ref name=Longrich2010>{{cite journal|last1=Longrich|first1=N. R.|last2=Currie|first2=P. J.|last3=Dong|first3=Z.|date=2010|title=A new oviraptorid (Dinosauria: Theropoda) from the Upper Cretaceous of Bayan Mandahu, Inner Mongolia|journal=Palaeontology|volume=53|issue=5|pages=945–960|doi=10.1111/j.1475-4983.2010.00968.x|bibcode=2010Palgy..53..945L |doi-access=free}}</ref>

In 2020, Czepiński analyzed several long-undescribed protoceratopsid specimens from the Udyn Sayr and Zamyn Khondt localities of the Djadokhta Formation. One specimen (MPC-D 100/551B) was shown to present skull traits that are intermediate between ''Bagaceratops rozhdestvenskyi'' (which is native to adjacent Bayan Mandahu and [[Barun Goyot]]) and ''P. andrewsi''. The specimen hails from the Udyn Sayr locality, where ''Protoceratops'' remains are dominant, and given the lack of more conclusive anatomical traits, Czepiński assigned the specimen as ''Bagaceratops'' sp. He explained that the presence of this ''Bagaceratops'' specimen in such unusual locality could be solved by: (1) the coexistence and [[sympatric]] (altogether) evolution of both ''Bagaceratops'' and ''Protoceratops'' at this one locality; (2) the rise of ''B. rozhdestvenskyi'' in a different region and eventual migration to Udyn Sayr; (3) [[Hybrid (biology)|hybridization]] between the two protoceratopsids given the near placement of both Bayan Mandahu and Djadokhta; (4) [[anagenetic]] (progressive evolution) evolutionary transition from ''P. andrewsi'' to ''B. rozhdestvenskyi''. Among scenarios, an anagenetic transition was best supported by Czepiński given the fact that no definitive ''B. rozhdestvenskyi'' fossils are found in Udyn Sayr, as expected from a hybridization event; MPC-D 100/551B lacks a well-developed accessory antorbital fenestra (hole behind the nostril openings), a trait expected to be present if ''B. rozhdestvenskyi'' had migrated to the area; and many specimens of ''P. andrewsi'' recovered at Udyn Sayr already feature a decrease in the presence of primitive premaxillary teeth, hence supporting a growing change in the populations.<ref name=Czepiński2020>{{cite journal|last1=Czepiński|first1=Ł.|date=2020|title=New protoceratopsid specimens improve the age correlation of the Upper Cretaceous Gobi Desert strata|journal=Acta Palaeontologica Polonica|volume=65|issue=3|pages=481–497|doi=10.4202/app.00701.2019|doi-access=free|url=http://www.app.pan.pl/archive/published/app65/app007012019.pdf}}</ref>