Editing Ungulate (section)

===Perissodactyl evolution ===
{{See also|Evolution of the horse}}
[[File:Eurohippus parvulus.jpg|thumb|left|Restoration of ''[[Eurohippus parvulus]]'', a mid- to late Eocene equid of Europe ([[Natural History Museum, Berlin]])]]
[[File:Sa-rhino-skin.jpg|thumb|The thick dermal [[Armour (anatomy)|armour]] of the Rhinoceros evolved at the same time as shearing [[tusks]].<ref>{{cite thesis |last=Hieronymus|first=Tobin L.|title=Osteological Correlates of Cephalic Skin Structures in Amniota: Documenting the Evolution of Display and Feeding Structures with Fossil Data |type=PhD dissertation |publisher=Ohio University |url=http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1237491191 |access-date=2022-11-12 |page=3|date=March 2009}}</ref>]]

Perissodactyls were thought to have evolved from the [[Phenacodontidae]], small, sheep-sized animals that were already showing signs of anatomical features that their descendants would inherit (the reduction of digit I and V for example).<ref name="Jehle-Condylarths"/> By the start of the [[Eocene]], 55&nbsp;million years ago (Mya), they had diversified and spread out to occupy several continents. [[Horse]]s and [[tapir]]s both evolved in North America;<ref name=MamEv>{{cite book|author= Savage, RJG, & Long, MR|year= 1986|title= Mammal Evolution: an illustrated guide|publisher= Facts on File|location= New York|isbn= 978-0-8160-1194-0|oclc= 12949777|url-access= registration|url= https://archive.org/details/mammalevolutioni0000sava}}</ref> rhinoceroses appear to have developed in [[Asia]] from tapir-like animals and then colonised the Americas during the middle Eocene (about 45&nbsp;Mya). Of the approximately 15 families, only three survive (McKenna and Bell, 1997; Hooker, 2005). These families were very diverse in form and size; they included the enormous [[Brontotheriidae|brontotheres]] and the bizarre [[Chalicotheriidae|chalicothere]]s. The largest perissodactyl, an Asian rhinoceros called ''[[Paraceratherium]]'', reached {{convert|15|tonne}}, more than twice the weight of an [[elephant]].<ref name=Benton>{{cite book|author= Benton, Michael J. |year= 1997 |title= Vertebrate Palaeontology |publisher= Chapman & Hall |location= London |page= 343 |isbn= 0-412-73810-4}}</ref>

It has been found in a cladistic study that the [[Anthracobunidae|anthracobunid]]s and the [[desmostylia]]ns – two lineages that have been previously classified as [[Afrotheria]]ns (more specifically closer to elephants) – have been classified as a clade that is closely related to the perissodactyls.<ref name="Cooper2014">{{Cite journal
  | doi     = 10.1371/journal.pone.0109232
  | pmid    = 25295875
  | title   = Anthracobunids from the Middle Eocene of India and Pakistan Are Stem Perissodactyls
  | journal = PLOS ONE
  | volume  = 9
  | issue   = 10
  | pages   = e109232
  | date    = 2014-10-08
  | last1   = Cooper
  | first1  = L. N.
  | last2   = Seiffert
  | first2  = E. R.
  | last3   = Clementz
  | first3  = M.
  | last4   = Madar
  | first4  = S. I.
  | last5   = Bajpai
  | first5  = S.
  | last6   = Hussain
  | first6  = S. T.
  | last7   = Thewissen
  | first7  = J. G. M.
|author5-link=Sunil Bajpai
|author7-link=Hans Thewissen
  | pmc=4189980
| bibcode = 2014PLoSO...9j9232C
 | doi-access = free
 }}</ref> The desmostylians were large amphibious quadrupeds with massive limbs and a short tail.<ref name="Gheerbrant-etal-2005">{{Harvnb|Gheerbrant|Domning|Tassy|2005|pp=95–6}}</ref>{{Missing long citation|date=July 2023}} They grew to {{Convert|1.8|m|ft|sigfig=1}} in length and were thought to have weighed more than {{convert|200|kg|lb}}. Their [[fossil]]s were known from the northern [[Pacific Rim]],<ref>{{Cite journal
  | last       = Gingerich
  | first      = Philip D.
  | author-link = Philip D. Gingerich
  | title      = Aquatic Adaptation and Swimming Mode Inferred from Skeletal Proportions in the Miocene Desmostylian ''Desmostylus''
  | year       = 2005
  | journal    = Journal of Mammalian Evolution
  | volume     = 12
  | issue      = 1/2
  | url        = http://deepblue.lib.umich.edu/bitstream/handle/2027.42/44971/10914_2005_Article_5719.pdf
  | doi        = 10.1007/s10914-005-5719-1
  | pages      = 183–194
| hdl = 2027.42/44971
 | s2cid = 7812089
 | hdl-access= free
  }}</ref> from southern [[Japan]] through [[Russia]], the [[Aleutian Islands]] and the Pacific coast of [[North America]] to the southern tip of [[Baja California]]. Their dental and skeletal form suggests desmostylians were aquatic [[herbivore]]s dependent on [[littoral]] habitats. Their name refers to their highly distinctive molars, in which each cusp was modified into hollow columns, so that a typical molar would have resembled a cluster of pipes, or in the case of worn molars, volcanoes. They were the only marine mammals to have gone extinct.

The South American [[South American native ungulates|meridiungulate]]s contain the somewhat tapir-like [[Pyrotheria|pyrotheres]] and [[Astrapotheria|astrapotheres]], the mesaxonic [[Litopterna|litoptern]]s and the diverse [[Notoungulata|notoungulates]]. As a whole, meridiungulates were said to have evolved from animals like ''[[Hyopsodus]]''.<ref name="Jehle-Condylarths"/> For a while their relationships with other ungulates were a mystery. Some [[paleontologists]] have even challenged the [[monophyly]] of Meridiungulata by suggesting that the pyrotheres may be more closely related to other mammals, such as [[Embrithopoda]] (an African order that were related to [[elephant]]s) than to other South American ungulates.<ref name=Shockey>{{cite journal |author1=Shockey, B.J. |author2=Anaya, F.  |name-list-style=amp | year = 2004 | title = ''Pyrotherium macfaddeni'', sp. nov. (late Oligocene, Bolivia) and the pedal morphology of pyrotheres | journal = Journal of Vertebrate Paleontology | volume = 24 | issue = 2 | pages = 481–488 | doi = 10.1671/2521|bibcode=2004JVPal..24..481S |s2cid=83680724 }}</ref> A recent study based on bone collagen has found that at least litopterns and the notoungulates were closely related to the perissodactyls.<ref name="Welker2015">{{cite journal |title=Ancient proteins resolve the evolutionary history of Darwin's South American ungulates |doi=10.1038/nature14249 |date=18 March 2015 |volume=522 |issue=7554 |journal=Nature |pages=81–84 |pmid=25799987 |last1=Welker |first1=F |last2=Collins |first2=MJ |last3=Thomas |first3=JA |last4=Wadsley |first4=M |last5=Brace |first5=S |last6=Cappellini |first6=E |last7=Turvey |first7=ST |last8=Reguero |first8=M |last9=Gelfo |first9=JN |last10=Kramarz |first10=A |last11=Burger |first11=J |last12=Thomas-Oates |first12=J |last13=Ashford |first13=DA |last14=Ashton |first14=PD |last15=Rowsell |first15=K |last16=Porter |first16=DM |last17=Kessler |first17=B |last18=Fischer |first18=R |last19=Baessmann |first19=C |last20=Kaspar |first20=S |last21=Olsen |first21=JV |last22=Kiley |first22=P |last23=Elliott |first23=JA |last24=Kelstrup |first24=CD |last25=Mullin |first25=V |last26=Hofreiter |first26=M |last27=Willerslev |first27=E |last28=Hublin |first28=JJ |last29=Orlando |first29=L |last30=Barnes |first30=I |last31=MacPhee |first31=RD |author2-link=Matthew Collins (academic)|author12-link=Jane Thomas-Oates|author17-link=Benedikt Kessler|author27-link=Eske Willerslev|bibcode=2015Natur.522...81W |hdl=11336/14769 |s2cid=4467386 |url=http://eprints.whiterose.ac.uk/91438/1/Welker_postprint.docx|hdl-access=free }}</ref>

The oldest known [[fossil]]s assigned to [[Equidae]] date from the early [[Eocene]], 54&nbsp;million years ago. They had been assigned to the genus ''[[Hyracotherium]]'', but the [[type species]] of that genus is now considered not a member of this family, but the other species have been split off into different genera.  These early Equidae were fox-sized animals with three toes on the hind feet, and four on the front feet. They were herbivorous browsers on relatively soft plants, and were already adapted for running. The complexity of their brains suggest that they already were alert and intelligent animals.<ref>{{cite book |editor=Palmer, D.|year=1999 |title= The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals|publisher= Marshall Editions|location=London|pages= 255|isbn= 978-1-84028-152-1}}</ref> Later species reduced the number of toes, and developed teeth more suited for grinding up grass and other tough plant food.

Rhinocerotoids diverged from other [[perissodactyls]] by the early Eocene. Fossils of ''[[Hyrachyus|Hyrachyus eximus]]'' found in North America date to this period. This small hornless ancestor resembled a tapir or small horse more than a rhino. Three families, sometimes grouped together as the [[Taxonomic rank|superfamily]] Rhinocerotoidea, evolved in the late Eocene: [[Hyracodontidae]], [[Amynodontidae]] and [[Rhinoceros|Rhinocerotidae]], thus creating an explosion of diversity unmatched for a while until environmental changes drastically eliminated several species.

The first tapirids, such as ''[[Heptodon]]'', appeared in the early Eocene.<ref>Ballenger, L. and Myers, P. (2001). [http://animaldiversity.ummz.umich.edu/site/accounts/information/Tapiridae.html "Family Tapiridae"], ''Animal Diversity Web''. Retrieved November 22, 2007.</ref> They appeared very similar to modern forms, but were about half the size, and lacked the proboscis. The first true tapirs appeared in the [[Oligocene]]. By the [[Miocene]], such genera as ''[[Miotapirus]]'' were almost indistinguishable from the extant species. Asian and American tapirs were believed to have diverged around 20 to 30&nbsp;million years ago; and tapirs migrated from North America to South America around 3&nbsp;million years ago, as part of the [[Great American Interchange]].<ref>{{Cite journal | doi = 10.1007/BF02077448 | last1 = Ashley | first1 = M.V. | last2 = Norman | first2 = J.E. | last3 = Stross | first3 = L. | year = 1996 | title = Phylogenetic analysis of the perissodactyl family tapiridae using mitochondrial cytochrome c oxidase (COII) sequences | journal =   Journal of Mammalian Evolution| volume = 3 | issue = 4| pages = 315–326 | s2cid = 24948320 }}</ref>

Perissodactyls were the dominant group of large terrestrial browsers right through the Oligocene. However, the rise of grasses in the Miocene (about 20&nbsp;Mya) saw a major change: the artiodactyl species with their more complex stomachs were better able to adapt to a coarse, low-nutrition diet, and soon rose to prominence. Nevertheless, many perissodactyl species survived and prospered until the late [[Pleistocene]] (about 10,000 years ago) when they faced the pressure of human hunting and habitat change.