Editing Moropus (section)

== Taxonomy ==

=== Early history ===
The first of the remains currently assigned to ''Moropus'' was a partial right [[maxilla]] (YPM 10030), uncovered at some point prior to 1873. In that year, the specimen was described YPM 10030, initially mistakenly attributed ''to Lophiodon''.<ref>{{Cite book |last=Leidy |first=Joseph |url=https://www.biodiversitylibrary.org/bibliography/61805 |title=Contributions to the extinct vertebrate fauna of the western territories |date=1873 |publisher=Govt. Print. Off |location=Washington}}</ref> After its discovery, multiple more complete specimens were discovered in the [[Miocene]] strata of the [[John Day Fossil Beds National Monument|John Day Fossil Beds]] of Oregon.<ref name=":0">{{Cite journal |last1=Holland |first1=William Jacob |author-link1=William Jacob Holland |last2=Peterson |first2=Olof August |date=1913 |title=The osteology of the Chalicotheroidea with special reference to a mounted skeleton of Moropus elatus Marsh, now installed in the Carnegie museum |url=https://www.biodiversitylibrary.org/part/211102 |journal=Memoirs of the Carnegie Museum |volume=3 |issue=2 |pages=189––406 |doi=10.5962/p.211102|doi-access=free }}</ref> In 1877, [[Othniel Charles Marsh]] formally described the specimens, assigning to them the genus name ''Moropus''. The type species of ''Moropus'', ''M. distans'', was based only on fragments of the hind foot.<ref name=":0" /><ref name=":1">{{Cite journal |last=Marsh |first=Othniel Charles |author-link=Othniel Charles Marsh |date=1877 |title=Notice of Some New Vertebrate Fossils |url=https://marsh.dinodb.com/marsh/Marsh%201877%20-%20Notice%20of%20some%20new%20vertebrate%20fossils.pdf |journal=American Journal of Science |volume=81 |issue=81 |pages=249–256|doi=10.2475/ajs.s3-14.81.249 |bibcode=1877AmJS...14..249M }}</ref> Two other species, ''M. elatus'' and ''M. senex'', were also described. At first, Marsh believed that ''Moropus'' belonged to the order [[Xenarthra|Edentata]], which historically included any mammal that lacked [[incisor]] teeth. Though he noted affinities with the African ''[[Ancylotherium]]'', he opted to erect a new [[Family (biology)|family]], Moropodidae, to exclusively include ''Moropus''.<ref name=":1" /> In 1908, geologist and palaeontologist [[Erwin Hinckley Barbour]] noted that ''Moropus'' had occasionally been treated as a form intermediate between edendates and [[Ungulate|ungulates]], though affirmed that it was definitely a true ungulate.<ref name=":2">{{Cite journal |last=Barbour |first=Erwin |date=1908-01-01 |title=The Skull of Moropus |url=https://digitalcommons.unl.edu/conservationsurvey/864/ |journal=Conservation and Survey Division}}</ref>

In 1913, Olof August Peterson named a new species of ''Moropus'', ''M. hollandi'', from limb elements recovered in 1901, at first mistakenly assigned to ''M. elatus''.<ref>{{Cite journal |last=Peterson |first=O. A. |date=1913-11-07 |title=A New Species of Moropus ( M. hollandi ) from the Base of the Middle Miocene of Western Nebraska |url=https://www.science.org/doi/10.1126/science.38.984.673.a |journal=Science |language=en |volume=38 |issue=984 |pages=673–680 |doi=10.1126/science.38.984.673.a |pmid=17732680 |issn=0036-8075|url-access=subscription }}</ref> In a 1913 [[monograph]] on chalicothere taxonomy, ''Moropus'' in particular, Peterson and [[William Jacob Holland]] recognised two additional species, ''M. matthewi'' and ''M. merriami'', and reassigned ''Moropus'' to [[Chalicotheriidae]].<ref name=":0" />

=== Invalid or reassigned species ===
In 1892, Barbour came into possession of a partial mammal skeleton from the [[Agate Fossil Beds National Monument]].<ref>{{Cite journal |last=Cockerell |first=T. D. A. |date=1923 |title=Fossil Mammals at the Colorado Museum of Natural History |url=https://www.jstor.org/stable/3693057 |journal=The Scientific Monthly |volume=17 |issue=3 |pages=271–277 |jstor=3693057 |issn=0096-3771}}</ref> He assigned the specimen to ''Moropus'', and named a new species, ''M. cooki'' (after Harold Cook, who discovered it) based on it. However, Peterson and Holland considered ''M. cooki'' a junior synonym of ''M. elatus''.<ref name=":0" /> In 1907, Holland named ''M. petersoni'', also from the Agate Fossil Beds, after Peterson.<ref>{{Cite journal |last=Holland |first=W. J. |date=1908 |title=A New Species of the Genus Moropus |url=https://www.jstor.org/stable/1634948 |journal=Science |volume=28 |issue=727 |pages=809–810 |doi=10.1126/science.28.727.809 |jstor=1634948 |pmid=17780444 |bibcode=1908Sci....28..809H |issn=0036-8075}}</ref> Later, in 1975, Margery Chalifoux Coombs suggested that ''M. petersoni'' was instead the same taxon as ''M. elatus'', and that its differences could be explained through [[sexual dimorphism]] {{See below|[[#Sexual dimorphism|below]]}}.<ref name=":3">{{Cite journal |last=Coombs |first=Margery Chalifoux |date=1975 |title=Sexual Dimorphism in Chalicotheres (Mammalia, Perissodactyla) |url=https://www.jstor.org/stable/2412697 |journal=Systematic Zoology |volume=24 |issue=1 |pages=55–62 |doi=10.2307/2412697 |jstor=2412697 |issn=0039-7989|url-access=subscription }}</ref> In 1935, Soviet palaeontologist K.K. Flerov named an Asian species of ''Moropus'', "M." ''betpakdalensis'' from Kazakhstan.<ref>{{Cite journal |last=Flerov |first=K. K. |date=1938 |title=Remains of Ungulata from Betpak–dala |journal=C. R. Acad. Sci. |volume=21 |pages=94–96}}</ref> This taxon has since been reassigned to a genus of its own, ''[[Borissiakia]]''.<ref name="butler1965">{{Cite journal |last=Butler |first=Percy Milton |author-link=Percy M. Butler |date=1965 |title=Fossil mammals of Africa No. 18: East African Miocene and Pleistocene chalicotheres |url=https://www.biodiversitylibrary.org/part/83495 |journal=Bulletin of the British Museum (Natural History) Geology |volume=10 |pages=163–237}}</ref> Another purported Asian ''Moropus'', "M''.''" ''huangheensis'', has also been reassigned to ''Borissiakia''.<ref>{{Cite journal |last1=Li |first1=Zhaoyu |last2=Mörs |first2=Thomas |last3=Zhang |first3=Yunxiang |last4=Xie |first4=Kun |last5=Li |first5=Yongxiang |date=2022-12-01 |title=New Material of Schizotheriine Chalicothere (Perissodactyla, Chalicotheriidae) from the Xianshuihe Formation (Early Miocene) of Lanzhou Basin, Northwest China |url=https://link.springer.com/article/10.1007/s10914-022-09619-3 |journal=Journal of Mammalian Evolution |language=en |volume=29 |issue=4 |pages=877–889 |doi=10.1007/s10914-022-09619-3 |issn=1573-7055}}</ref>

=== Taxonomy ===
Chalicotheres are part of the order [[Perissodactyla]], which includes modern [[Equidae|equines]], [[Rhinoceros|rhinoceroses]], and [[Tapir|tapirs]], as well as extinct groups like [[Brontotheriidae|brontotheres]].<ref name="MamEv2">{{cite book |author1=Savage, RJG |url=https://archive.org/details/mammalevolutioni0000sava |title=Mammal Evolution: an illustrated guide |author2=Long, MR |publisher=Facts on File |year=1986 |isbn=0-8160-1194-X |location=New York |pages=[https://archive.org/details/mammalevolutioni0000sava/page/198 198–199] |url-access=registration}}</ref><ref name=":4">{{Cite journal |last1=Holbrook |first1=Luke T. |last2=Lucas |first2=Spencer G. |last3=Emry |first3=Robert J. |date=2004 |title=Skulls of the Eocene Perissodactyls (Mammalia) "Homogalax" and "Isectolophus" |url=https://www.jstor.org/stable/4524789 |journal=Journal of Vertebrate Paleontology |volume=24 |issue=4 |pages=951–956 |doi=10.1671/0272-4634(2004)024[0951:SOTEPM]2.0.CO;2 |issn=0272-4634 |jstor=4524789 |s2cid=86289060|url-access=subscription }}</ref> As the early evolution of perissodactyls is still unresolved, their closest relatives among other perissodactyl groups is obscure.<ref name=":4" /> They are generally placed as part of the clade [[Ancylopoda]] alongside their close relatives [[Lophiodontidae]]. Many studies considered them as closer to [[Perissodactyla|Ceratomorpha]] (which includes tapirs and rhinoceroses) than [[Equoidea]].<ref>{{Cite journal |last=Froehlich |first=David J. |date=1999 |title=Phylogenetic Systematics of Basal Perissodactyls |url=https://www.jstor.org/stable/4523976 |journal=Journal of Vertebrate Paleontology |volume=19 |issue=1 |pages=140–159 |bibcode=1999JVPal..19..140F |doi=10.1080/02724634.1999.10011129 |issn=0272-4634 |jstor=4523976|url-access=subscription }}</ref><ref>{{Citation |last=Tsoukala |first=Evangelia |title=The Fossil Record of Chalicotheres (Mammalia: Perissodactyla: Chalicotheriidae) in Greece |date=2022 |work=Fossil Vertebrates of Greece Vol. 2 |pages=501–517 |editor-last=Vlachos |editor-first=Evangelos |url=https://link.springer.com/10.1007/978-3-030-68442-6_15 |access-date=2024-08-22 |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-030-68442-6_15 |isbn=978-3-030-68441-9|url-access=subscription }}</ref> A 2004 [[Cladistics|cladistic]] study alternatively recovered Ancylopoda as sister to all modern [[Perissodactyla|perissodactyls]] (which includes Equoidea and Ceratomorpha), with the [[Brontotheriidae|brontotheres]] [[Basal (phylogenetics)|basal]] to both.<ref>{{Cite journal |last1=Hooker |first1=J. J. |last2=Dashzeveg |first2=D. |date=2004 |title=The origin of chalicotheres (Perissodactyla, Mammalia) |journal=Palaeontology |language=en |volume=47 |issue=6 |pages=1363–1386 |bibcode=2004Palgy..47.1363H |doi=10.1111/j.0031-0239.2004.00421.x |issn=1475-4983 |s2cid=83720739 |doi-access=free}}</ref>

In their 1914 monograph on chalicotheres, Holland and Peterson listed three [[Subfamily|subfamilies]]: Moropodinae (''Ancylotherium'', ''Moropus'', and ''Nestoritherium''), Macrotheriinae (including ''[[Chalicotherium]]'', ''Circotherium'', and ''Macrotherium'') and [[Schizotheriinae]] (''[[Peratherium|Pernatherium]]'' and ''[[Schizotherium]]'').<ref name=":0" /> Macrotheriinae was subsequently synonymised with the existing [[Chalicotheriinae]]. Palaeontologist [[Arthur Smith Woodward]], in 1925, concurred with the system used by Holland and Peterson, and only altered the placements of a few genera.<ref name=":5">{{Cite journal |last1=Colbert |first1=Edwin Harris |author-link1=Edwin H. Colbert |last2=Brown |first2=Barnum |author-link2=Barnum Brown |date=1935 |title=Distributional and phylogenetic studies on Indian fossil mammals. 3, A classification of the Chalicotherioidea. |url=https://digitallibrary.amnh.org/items/7cfd1925-eb6f-449b-8bbe-60f9a8f71028 |journal=American Museum Novitates |issue=798}}</ref> [[William Diller Matthew]] instead split chalicotheres into just two subfamilies, Chalicotheriinae and [[Eomoropidae|Eomoropinae]]. The former was divided into two clades based on whether their teeth were [[Molar (tooth)|brachydont]] (short-crowned) or [[hypsodont]] (high-crowned): ''Moropus'' fell into the latter category.<ref name=":6">{{Cite journal |last=Matthew |first=William Diller |author-link=William Diller Matthew |date=1929 |title=Critical Observations Upon Siwalik Mammals |journal=Bulletin of the American Museum of Natural History |pages=516–524}}</ref> In 1935, [[Edwin H. Colbert]] retained this system, though divided Chalicotheriinae into the [[Tribe (biology)|tribes]] Chalicotheriini and Schizotheriini.<ref name=":5" /> Currently, they are both treated as tribes,<ref name="butler1965"/> and eomoropids have been removed from Chalicotheriidae entirely.<ref>{{Cite journal |last=Holbrook |first=L |date=1999 |title=The Phylogeny and Classification of Tapiromorph Perissodactyls (Mammalia) |url=https://doc.rero.ch/record/20950/files/PAL_E4153.pdf |journal=Cladistics |language=en |volume=15 |issue=3 |pages=331–350 |doi=10.1006/clad.1999.0107}}</ref><ref>{{Cite journal |last1=Missiaen |first1=Pieter |last2=Gingerich |first2=Philip D. |date=2012 |title=New Early Eocene Tapiromorph Perissodactyls from the Ghazij Formation of Pakistan, with Implications for Mammalian Biochronology in Asia |url=http://www.app.pan.pl/article/item/app20100093.html |journal=Acta Palaeontologica Polonica |language=en |volume=57 |issue=1 |pages=21–34 |doi=10.4202/app.2010.0093 |issn=0567-7920|hdl=1854/LU-3178691 |hdl-access=free }}</ref> ''Moropus'' is currently classified under Schizotheriinae.<ref>{{Cite journal |last1=Coombs |first1=Margery C. |last2=Hunt |first2=Robert M. |last3=Stepleton |first3=Ellen |last4=Albright |first4=L. Barry |last5=Fremd |first5=Theodore J. |date=2001-08-22 |title=Stratigraphy, chronology, biogeography, and taxonomy of early Miocene small chalicotheres in North America |url=http://www.tandfonline.com/doi/abs/10.1671/0272-4634%282001%29021%5B0607%3ASCBATO%5D2.0.CO%3B2 |journal=Journal of Vertebrate Paleontology |language=en |volume=21 |issue=3 |pages=607–620 |doi=10.1671/0272-4634(2001)021[0607:SCBATO]2.0.CO;2 |issn=0272-4634|url-access=subscription }}</ref>