Editing Perissodactyla (section)

===Outer taxonomy===
Traditionally, the odd-toed ungulates were classified with other mammals such as [[Even-toed ungulate|artiodactyls]], [[hyrax]]es, [[elephants]] and other "ungulates". A close family relationship with hyraxes was suspected based on similarities in the construction of the ear and the course of the [[carotid artery]].

Molecular genetic studies, however, have shown the ungulates to be [[Polyphyly|polyphyletic]], meaning that in some cases the similarities are the result of [[convergent evolution]] rather than [[common ancestor|common ancestry]]. Elephants and hyraxes are now considered to belong to [[Afrotheria]], so are not closely related to the perissodactyls. These in turn are in the [[Laurasiatheria]], a superorder that had its origin in the former supercontinent [[Laurasia]]. Molecular genetic findings suggest that the cloven [[Artiodactyla]] (containing the [[cetacea]]ns as a deeply nested subclade) are the sister taxon of the Perissodactyla; together, the two groups form the [[Ungulate|Euungulata]].<ref name="Graur et al. 1997">{{cite journal|author1=Dan Graur|author2=Manolo Gouy|author3=Laurent Duret|title=Evolutionary Affinities of the Order Perissodactyla and the Phylogenetic Status of the Superordinal taxa Ungulata and Altungulata Molecular Phylogenetics and Evolution|year= 1997|pages= 195–200|doi= 10.1006/mpev.1996.0391|volume= 7|issue=2|journal=Molecular Phylogenetics and Evolution|pmid=9126561}}</ref> More distant are the [[bat]]s (Chiroptera) and [[Ferae]] (a common taxon of carnivorans, [[Carnivora]], and pangolins, [[Pholidota]]).<ref name="Hu et al. 2012">{{cite journal|author1=Jingyang Hu|author2=Zhang Yaping|author3=Li Yu|title=Summary of Laurasiatheria (Mammalia) Phylogeny|journal=Zoological Research|year=2012|pages=65–74|doi=10.3724/sp.j.1141.2012.e05-06e65|pmid=23266984|volume=33|issue=6|s2cid=30067369 |doi-access=free|hdl=1807/64815|hdl-access=free}}</ref> In a discredited alternative scenario, a close relationship exists between perissodactyls, carnivorans, and bats, this assembly comprising the [[Pegasoferae]].<ref name="Nishihara et al. 2006">{{cite journal|author1=Hidenori Nishihara|author2=Masami Hasegawa|author3=Norihiro Okada|title=Pegasoferae, an unexpected mammalian clade revealed by tracking ancient retroposon insertions|journal=Proceedings of the National Academy of Sciences USA |volume=103 |issue=26|pages=9929–9934 |doi=10.1073/pnas.0603797103 |pmid=16785431|pmc=1479866|year=2006|bibcode=2006PNAS..103.9929N|doi-access=free}}</ref>

{| class="wikitable" style="float:right;"
|-
|+ Internal taxonomy of the Euungulata after Welker ''et al.'' 2015<ref name="Welker et al. 2015"/>
|-
|{{Clade|style=font-size:75%; line-height:100%
|label1=[[Euungulata]]
|1={{Clade
     |1=[[Artiodactyla]] (Even-toed ungulates and cetaceans)
     |label2=[[Panperissodactyla]]
     |2={{Clade
          |1='''Perissodactyla'''(Odd-toed ungulates)
          |2=[[extinct|†]] [[Meridiungulata]] (South American ungulates,<br />especially [[Notoungulata]] and [[Litopterna]])
          }}
     }}
}}
|}

According to studies published in March 2015, odd-toed ungulates are in a close family relationship with at least some of the so-called [[South American native ungulates|Meridiungulata]], a very diverse group of mammals living from the Paleocene to the Pleistocene in South America, whose systematic unity is largely unexplained. Some of these were classified based on their paleogeographic distribution. However, a close relationship can be worked out to perissodactyls by [[protein sequencing]] and comparison with fossil collagen from remnants of phylogenetically young members of the Meridiungulata (specifically ''[[Macrauchenia]]'' from the [[Litopterna]] and ''[[Toxodon]]'' from the [[Notoungulata]]). Both kinship groups, the odd-toed ungulates and the Litopterna-Notoungulata, are now in the higher-level taxon of [[Panperissodactyla]]. This kinship group is included among the Euungulata, which also contains the even-toed ungulates (Artiodactyla). The separation of the Litopterna-Notoungulata group from the perissodactyls probably took place before the [[Cretaceous–Paleogene extinction event]]. "Condylarths" can probably be considered the starting point for the development of the two groups, as they represent a heterogeneous group of primitive ungulates that mainly inhabited the northern hemisphere in the [[Paleogene]].<ref name="Welker et al. 2015">{{cite journal|author1=Frido Welker|author2=Matthew J. Collins|author3=Jessica A. Thomas|author4=Marc Wadsley|author5=Selina Brace|author6=Enrico Cappellini|author7=Samuel T. Turvey|author8=Marcelo Reguero|author9=Javier N. Gelfo|author10=Alejandro Kramarz|author11=Joachim Burger|author12=Thomas Jane Oates|author13=David A. Ashford|author14=Peter D. Ashton|author15=Keri Rowsell|author16=Duncan M. Porter|author17=Benedikt Kessler|author18=Roman Fischer|author19=Carsten Baessmann|author20=Stephanie Kaspar|author21=Jesper V. Olsen|author22=Patrick Kiley|author23=James A. Elliott|author24=Christian D. Kelstrup|author25=Victoria Mullin|author26=Michael Hofreiter|author27=Eske Willerslev|author28=Jean-Jacques Hublin|author29=Ludovic Orlando|author30=Ian Barnes|author31=Ross DE MacPhee|title=Ancient protein resolve the evolutionary history of Darwin's South American ungulates|journal=Nature|doi=10.1038/nature14249|volume=522|issue=7554|pages=81–84|pmid=25799987|year=2015|bibcode=2015Natur.522...81W|s2cid=4467386|url=http://eprints.whiterose.ac.uk/91438/1/Welker_postprint.docx|hdl=11336/14769|hdl-access=free}}</ref><ref>{{cite journal|author1=Ross MacPhee|author2=Frido Welker|author3=Jessica Thomas|author4=Selina Brace|author5=Enrico Cappellini|author6=Samuel Turvey|author7=Ian Barnes|author8=Marcelo Reguero|author9=Javier Gelfo|author10=Alejandro Kramarz|title=Ancient protein sequencing Resolves litoptern and notoungulate superordinal affinities|journal=The History of Life: A View from the Southern Hemisphere|year=2014|page=186}}</ref>