Editing Ungulate

{{Short description|Group of animals that walk on the tips of their toes or hooves}}
{{For|elephants and relatives, sometimes called ungulates or subungulates|Paenungulata}}
{{Automatic taxobox
| fossil_range = {{fossilrange|Thanetian|recent|earliest=66|[[Paleocene]]–present}}
| image = Clade Ungulata Two Orders.jpg
| image_caption = Image from top to left with [[artiodactyls]] at the top and [[Perissodactyla]] at the bottom: [[giraffe]], [[plains bison]], [[dromedary]],  [[red deer]], [[wild boar]], [[orca]] ([[Cetacea]]), [[plains zebra]], [[Indian rhinoceros]], and [[Brazilian tapir]].
| taxon = Euungulata
| authority = Waddell ''et al.'', 2001<ref name="euungulata">Peter J. Waddell, Hirohisa Kishino, Rissa Ota (2001). "A Phylogenetic Foundation for Comparative Mammalian Genomics". ''Genome Informatics'' '''12''': 141–154, {{doi|10.11234/gi1990.12.141}}.</ref>
| subdivision_ranks = Orders and clades
| subdivision = * ''Clade'': [[Panperissodactyla]]
** Family: †[[Phenacodontidae]]?
** ''Clade'': †'''[[Anthracobunia]]'''
** Order: †[[Desmostylia]](?)<ref name="Cooper2014"/>
** ''Clade'': †[[Litopterna]]
** ''Clade'': †[[Notoungulata]]
** Order: [[Odd-toed ungulate|Perissodactyla]]
* ''Clade'': '''[[Artiodactyla|Panartiodactyla]]'''
** Order: †[[Arctocyonia]]?
** Order: †[[Mesonychia]]?
** Family: †[[Periptychidae]]?
** Order: [[Even-toed ungulate|Artiodactyla]]
| synonyms = * Cetungulata {{smalldiv|Irwin and Wilson, 1993<ref>Irwin, D.M. and Wilson, A.C. (1993). "Limitations of molecular methods for establishing the phylogeny of mammals, with special reference to the position of elephants". In: F.S. Szalay, M.J. Novacek, and M.C. McKenna (eds.), ''Mammal Phylogeny: Placentals''. pp. 257–267, Springer-Verlag, New York.</ref>}}
}}

'''Ungulates''' ({{IPAc-en|ˈ|ʌ|ŋ|ɡ|j|ʊ|l|eɪ|t|s|,_|-|ɡ|j|ə|-|,_|-|l|ɪ|t|s|,_|-|l|ə|t|s}} {{respell|UNG|gyuu|layts|,_-|gyə|-,_-|lits|,_-|ləts}}) are members of the diverse [[clade]] '''Euungulata''' ("true ungulates"), which primarily consists of large mammals with [[Hoof|hooves]]. Once part of the clade "Ungulata" along with the clade [[Paenungulata]], "Ungulata" has since been determined to be a [[polyphyletic]] and thereby invalid clade based on molecular data. As a result, true ungulates had since been reclassified to the newer clade Euungulata in 2001 within the clade [[Laurasiatheria]] while [[Paenungulata]] has been reclassified to a distant clade [[Afrotheria]].<ref>{{cite journal|last1=Gheerbrant|first1=Emmanuel|last2=Filippo|first2=Andrea|last3=Schmitt|first3=Arnaud|year=2016|title=Convergence of Afrotherian and Laurasiatherian Ungulate-Like Mammals: First Morphological Evidence from the Paleocene of Morocco|journal=PLOS ONE|volume=11|issue=7|pages=e0157556 |doi=10.1371/journal.pone.0157556 |pmid=27384169 |pmc=4934866 |bibcode=2016PLoSO..1157556G |doi-access=free }}</ref>  Living ungulates are divided into two orders: [[Perissodactyla]] including [[Equidae|equines]], [[rhinoceros]]es, and [[tapir]]s; and [[Artiodactyla]] including [[Bos|cattle]], [[antelope]], [[Sus (genus)|pig]]s, [[giraffe]]s, [[camel]]s, [[Ovis|sheep]], [[deer]], and [[Hippopotamidae|hippopotamus]]es, among others. [[Cetacean]]s such as [[Whale|whales]], [[Dolphin|dolphins]], and [[Porpoise|porpoises]] are also classified as artiodactyls, although they do not have hooves. Most terrestrial ungulates use the hoofed tips of their toes to support their body weight while standing or moving. Two other orders of ungulates, [[Notoungulata]] and [[Litopterna]], both native to South America, became extinct at the end of the Pleistocene, around 12,000 years ago.

The term means, roughly, "being hoofed" or "hoofed animal". As a descriptive term, "ungulate" normally excludes cetaceans as they do not possess most of the typical [[Morphology (biology)|morphological]] characteristics of other ungulates, but recent discoveries indicate that they were also descended from early [[artiodactyls]].<ref name="Genomes">{{Cite journal | title = Analyses of mitochondrial genomes strongly support a hippopotamus-whale clade | volume = 265 | issue = 1412 | year = 1998 | pages = 2251–5 | journal = [[Proceedings of the Royal Society B]] | author = Ursing, B. M. |author2=Arnason, U.  | doi = 10.1098/rspb.1998.0567 | pmid = 9881471 | pmc = 1689531}}</ref> Ungulates are typically herbivorous and many employ specialized [[Gut microbiota|gut bacteria]] to enable them to digest cellulose, though some members may deviate from this: several species of [[Suidae|pigs]] and the extinct [[entelodont]]s are omnivorous, while cetaceans and the extinct [[mesonychia]]ns are carnivorous.

==Etymology==
Ungulate is from the [[Late Latin]] adjective {{Lang|la|ungulatus}} {{gloss|hoofed}}. {{Lang|la|Ungulatus}} is a [[diminutive]] form of Latin {{Lang|la|unguis}} {{gloss|nail}} (finger nail; toe nail).<ref>{{cite web |url=https://www.etymonline.com/search?q=ungulate|title= Online Etymology Dictionary |website= www.etymonline.com |access-date= 6 June 2022}}</ref>

==Classifications==

===History===
Euungulata is a clade (or in some taxonomies, a grand order) of mammals. The two extant orders of ungulates are the [[Odd-toed ungulate|Perissodactyla (odd-toed ungulates)]] and [[Even-toed ungulate|Artiodactyla (even-toed ungulates)]]. [[Hyrax|Hyracoidea (hyraxes)]], [[Sirenia|Sirenia (sea cows, dugongs and manatees)]] and [[Proboscidea|Proboscidea (elephants)]] were in the past grouped within the clade "Ungulata", later found to be a [[polyphyletic]] and invalid clade. The three orders of Paenungulata are considered a clade and grouped in the Afrotheria clade, while Euungulata is grouped under the [[Laurasiatheria]] clade.<ref name="euungulata"/>

In 2009, morphological<ref>{{cite journal | last1 = Asher | first1 = RJ | last2 = Bennet | first2 = N | last3 = Lehmann | first3 = T | year = 2009 | title = The new framework for understanding placental mammal evolution | journal = BioEssays | volume = 31 | issue = 8| pages = 853–864 | doi=10.1002/bies.200900053 | pmid=19582725| s2cid = 46339675 | doi-access = free }}</ref><ref name="Tabuce">{{cite journal | last1 = Tabuce | first1 = R. | last2 = Marivaux | first2 = L. | last3 = Adaci | first3 = M. | last4 = Bensalah | first4 = M. | last5 = Hartenberger | first5 = J. L. | display-authors = etal   | year = 2007 | title = Early tertiary mammals from north Africa reinforce the molecular afrotheria clade | journal = Proceedings of the Royal Society B | volume = 274 | issue = 1614| pages = 1159–1166 | doi=10.1098/rspb.2006.0229 | pmid=17329227 | pmc=2189562}}</ref><ref name="Seiffert">{{cite journal | last1 = Seiffert | first1 = E | year = 2007 | title = A new estimate of afrotherian phylogeny based on simultaneous analysis of genomic, morphological, and fossil evidence | journal = BMC Evol Biol | volume = 7 | page = 13 | doi = 10.1186/1471-2148-7-224 | pmid = 17999766 | pmc = 2248600 | doi-access = free }}</ref><ref name="SanchezVillagra">{{cite journal | last1 = Sanchez-Villagra | first1 = M. R. | last2 = Narita | first2 = Y. | last3 = Kuratani | first3 = S. | year = 2007 | title = Thoracolumbar vertebral number: the first skeletal synapomorphy for afrotherian mammals | journal = Syst Biodivers | volume = 5 | pages = 1–17 | doi = 10.1017/S1477200006002258 | s2cid = 85675984 }}</ref> and molecular<ref>{{cite journal | last1 = Springer | first1 = MS | last2 = Stanhope | first2 = MJ | last3 = Madsen | first3 = O | last4 = de Jong | first4 = WW | year = 2004 | title = Molecules consolidate the placental mammal tree | journal = Trends Ecol Evol | volume = 19 | issue = 8| pages = 430–438 | doi=10.1016/j.tree.2004.05.006 | pmid=16701301| s2cid = 1508898 }}</ref><ref>{{cite journal | last1 = Robinson | first1 = M. A. Yang | last2 = Fu | first2 = T. J. | last3 = Ferguson-Smith | first3 = B. | year = 2004 | title = Cross-species chromosome painting in the golden mole and elephant-shrew: support for the mammalian clades Afrotheria and Afroinsectiphillia but not Afroinsectivora | journal = Proceedings of the Royal Society B | volume = 271 | issue = 1547| pages = 1477–1484 | doi=10.1098/rspb.2004.2754 | pmid=15306319 | pmc=1691750}}</ref> work found that aardvarks, hyraxes, sea cows, and elephants were more closely related to each other and to [[sengi]]s, [[tenrec]]s, and [[golden mole]]s than to the perissodactyls and artiodactyls, and form the clade [[Afrotheria]]. Elephants, sea cows, and hyraxes were grouped together in the clade [[Paenungulata]], while the aardvark has been considered as either a close relative to them or a close relative to sengis in the clade [[Afroinsectiphilia]].<ref name=Seiffert2007>{{cite journal | author = Seiffert, E.R. | year = 2007 | title = A new estimate of afrotherian phylogeny based on simultaneous analysis of genomic, morphological, and fossil evidence | journal = BMC Evolutionary Biology | volume = 7 | pages = 13 | url= | doi = 10.1186/1471-2148-7-224 | pmid = 17999766 | last2 = Guillon | first2 = JM | pmc=2248600 | issue=1 | doi-access = free }}</ref> This is a striking example of [[convergent evolution]].<ref>{{cite book|last=Dawkins|first=Richard|title=The Ancestor's Tale|publisher=Mariner Books|location=Boston|year=2005|page=[https://archive.org/details/ancestorstale00rich_0/page/195 195]|isbn=978-0-618-61916-0|url=https://archive.org/details/ancestorstale00rich_0/page/195}}</ref>

There is some dispute as to whether this smaller Euungulata is a [[cladistic]] (evolution-based) group, or merely a [[phenetics|phenetic]] group ([[Form classification|form taxon]]) or [[folk taxon]] (similar, but not necessarily related). Some studies have indeed found the [[mesaxonia]]n ungulates and paraxonian ungulates to form a monophyletic lineage,<ref name=asher>{{cite journal|last1=Asher|first1=Robert J|last2=Helgen|first2=Kristofer M|title=Nomenclature and placental mammal phylogeny|journal=BMC Evolutionary Biology|volume=10|issue=1|year=2010|pages=102|doi=10.1186/1471-2148-10-102|pmid=20406454|pmc=2865478 |doi-access=free }}</ref><ref name=Spauldingetal2009>{{cite journal|pmc=2740860 | pmid=19774069 | doi=10.1371/journal.pone.0007062 | volume=4 | issue=9 | title=Relationships of Cetacea (Artiodactyla) among mammals: increased taxon sampling alters interpretations of key fossils and character evolution | year=2009 | journal=PLOS ONE | pages=e7062|bibcode = 2009PLoSO...4.7062S|editor1-last=Farke|editor1-first=Andrew Allen|last1=Spaulding|first1=Michelle|last2=O'Leary|first2=Maureen A.|last3=Gatesy|first3=John | doi-access=free }}</ref><ref name= "Nery">{{Cite journal | last1 = Nery | first1 = M. F. | last2 = González | first2 = D. M. J. | last3 = Hoffmann | first3 = F. G. | last4 = Opazo | first4 = J. C. | title = Resolution of the laurasiatherian phylogeny: Evidence from genomic data | doi = 10.1016/j.ympev.2012.04.012 | journal = Molecular Phylogenetics and Evolution | volume = 64 | issue = 3 | pages = 685–689 | year = 2012 | pmid =  22560954}}</ref> closely related to either the [[Ferae]] (the [[carnivora]]ns and the [[pangolin]]s)<ref>{{cite journal|last1=Beck|first1=Robin MD|last2=Bininda-Emonds|first2=Olaf RP|last3=Cardillo|first3=Marcel|last4=Liu|first4=Fu-Guo|last5=Purvis|first5=Andy|journal=BMC Evolutionary Biology|volume=6|issue=1|year=2006|pages=93|doi=10.1186/1471-2148-6-93|title=A higher-level MRP supertree of placental mammals|pmid=17101039|pmc=1654192 |doi-access=free }}</ref><ref>{{cite journal |author=Zhou, X. |year=2011 |title=Phylogenomic analysis resolves the interordinal relationships and rapid diversification of the Laurasiatherian mammals  |journal=[[Systematic Biology]] |doi=10.1093/sysbio/syr089 |volume=61 |pages=150–64 |pmid=21900649 |pmc=3243735 |issue=1 |first2=S. |last2=Xu |first3=J. |last3=Xu |first4=B. |last4=Chen |first5=K. |last5=Zhou |first6=G. |last6=Yang|display-authors=etal}}</ref> in the clade [[Fereuungulata]] or to the [[bat]]s.<ref>{{cite web | title = Researchers Greatly Improve Evolutionary Tree of Life for Mammals | url = http://newsroom.ucr.edu/2729 | url-status = dead | archive-url = https://web.archive.org/web/20111001174523/http://newsroom.ucr.edu/2729 | archive-date = 1 October 2011 | date = 22 September 2011 | website = UCR Newsroom | publisher = UC Riverside | access-date = 9 April 2021}}</ref> Other studies found the two orders not that closely related, as some place the perissodactyls as close relatives to bats and Ferae in [[Pegasoferae]]<ref>{{Cite journal | last1 = Nishihara | first1 = H.| last2 = Hasegawa | first2 = M.| last3 = Okada | first3 = N.| title = Pegasoferae, an unexpected mammalian clade revealed by tracking ancient retroposon insertions | doi = 10.1073/pnas.0603797103 | journal = [[Proceedings of the National Academy of Sciences of the United States of America|Proceedings of the National Academy of Sciences]]| volume = 103 | issue = 26 | pages = 9929–9934 | year = 2006 | pmid = 16785431| pmc = 1479866| bibcode = 2006PNAS..103.9929N| doi-access = free}}</ref> and others place the artiodactyls as close relatives to bats.<ref name=Gatesy>{{cite journal | doi=10.1016/j.ympev.2012.10.012 | volume=66 | issue=2 | title=A phylogenetic blueprint for a modern whale | journal=Molecular Phylogenetics and Evolution | pages=479–506 | pmid=23103570 | last1 = Gatesy | first1 = J | last2 = Geisler | first2 = JH | last3 = Chang | first3 = J | last4 = Buell | first4 = C | last5 = Berta | first5 = A | last6 = Meredith | first6 = RW | last7 = Springer | first7 = MS | last8 = McGowen | first8 = MR| date=February 2013 }}</ref>

===Taxonomy===
[[File:Zebras Ngorongoro Crater.jpg|thumb|[[Plains zebra]]]]
[[File:Diceros bicornis.jpg|thumb|[[Black rhinoceros]]]]
[[File:Elaphurus davidianus 001.jpg|thumb|[[Père David's deer]]]]
[[File:Hippopotamus - 04.jpg|thumb|[[Hippopotamus]]]]
[[File:Bluewhale877.jpg|thumb|[[Blue whale]]]]
[[File:Comdolph.jpg|thumb|[[Common dolphin]]]]
Below is a simplified taxonomy (assuming that ungulates do indeed form a natural grouping) with the extant families, in order of the relationships. Keep in mind that there were still some grey areas of conflict, such as the case with the relationship between the [[pecora]]n families and the [[baleen whale]] families. See each family for the relationships of the species as well as the controversies in their respective articles.

* '''Euungulata<ref name=asher/>'''
** '''[[Odd-toed ungulate|Perissodactyla]]''' (Mesaxonian ungulates)
*** '''Hippomorpha'''
**** [[Equidae]]: Horses, asses and zebras
*** '''[[Ceratomorpha]]'''
**** [[Tapiridae]]: Tapirs
**** [[Rhinocerotidae]]: Rhinoceroses
** '''[[Artiodactyla]] (= [[Cetartiodactyla]])''' (Paraxonian ungulates)
*** '''[[Tylopoda]]'''
**** [[Camelidae]]: Camels and llamas
*** '''Artiofabula'''
**** '''[[Suina]]'''
***** [[Tayassuidae]]: Peccaries
***** [[Suidae]]: Pigs
**** '''[[Cetruminantia]]'''
***** '''[[Ruminantia]]'''
****** [[Tragulidae]]: Chevrotains
****** '''[[Pecora|Cervoidea]]'''
******* [[Antilocapridae]]: Pronghorn
******* [[Giraffidae]]: Giraffes and okapi
******* [[Cervidae]]: Deer
******* [[Moschidae]]: Musk deer
******* [[Bovidae]]: Cattle and antelopes
***** '''[[Whippomorpha]]'''
****** [[Hippopotamidae]]: Hippopotamuses
****** '''[[Cetacea]]'''
******* '''[[Mysticeti]]'''
******** [[Balaenidae]]: Bowhead and right whales
******** [[Cetotheriidae]]: Pygmy right whale
******** [[Balaenopteridae]]: Rorquals
******* '''[[Odontoceti]]'''
******** '''[[Physeteroidea]]'''
********* [[Physeteridae]]: Sperm whale
********* [[Kogiidae]]: Lesser sperm whales
******** '''[[Platanistoidea]]'''
********* [[Platanistidae]]: Indian river dolphins
******** '''[[Ziphioidea]]'''
********* [[Ziphiidae]]: Beaked whales
******** '''[[Lipotidae|Lipotoidea]]'''
********* [[Lipotidae]]: Baiji (functionally extinct)
******** '''[[Inioidea]]'''
********* [[Iniidae]]: Amazonian river dolphins
********* [[Pontoporiidae]]: La Plata dolphin
******** '''[[Delphinoidea]]'''
********* [[Monodontidae]]: Beluga and narwhal
********* [[Phocoenidae]]: Porpoises
********* [[Delphinidae]]: Oceanic dolphins

===Phylogeny===
Below is the general consensus of the phylogeny of the ungulate families.<ref name=Gatesy/><ref>{{cite journal | last1 = Kim | first1 = S. L. | last2 = Thewissen | first2 = J. G. | last3 = Churchill | first3 = M. M. | last4 = Suydam | first4 = R. S. | last5 = Ketten | first5 = D. R. | last6 = Clementz | first6 = M. T. | year = 2014 | title = Unique biochemical and mineral composition of whale ear bones | url = http://darchive.mblwhoilibrary.org/bitstream/1912/6709/1/Kim_2014_Physiol_Biochem_Zool.pdf| journal = Physiological and Biochemical Zoology | volume = 87 | issue = 4| pages = 576–584 | doi=10.1086/676309| pmid = 24940922 | hdl = 1912/6709 | s2cid = 27076616 | hdl-access = free }}</ref>
{{clade|style=font-size:100%
|label1='''Euungulata'''
|1={{Clade
   |label1=[[Perissodactyla]]
   |1={{Clade
      |1=[[Equidae]][[File:Equus quagga (white background).jpg|50 px]]
      |label2=
      |2={{Clade
         |1=[[Tapiridae]][[File:Tapir white background.jpg|50 px]]
         |2=[[Rhinocerotidae]][[File:Rhino white background.jpg|50 px]]
         }}
      }}
   |label2=[[Artiodactyla]]
   |2={{Clade
      |label1=[[Tylopoda]]
      |1=[[Camelidae]][[File:Cladogram of Cetacea within Artiodactyla (Camelus bactrianus).png|50 px]]
      |label2=[[Artiofabula]]
      |2={{Clade
         |label1=[[Suina]]
         |1={{Clade
            |1=[[Tayassuidae]][[File:Pecari tajacu white background.jpg|50 px]]
            |2=[[Suidae]][[File:Recherches pour servir à l'histoire naturelle des mammifères (Pl. 80) (white background).jpg|50 px]]
            }}
         |label2=[[Cetruminantia]]
         |2={{Clade
            |label1=[[Ruminantia]]
            |1={{Clade
               |1=[[Tragulidae]][[File:Tragulus napu - 1818-1842 - Print - Iconographia Zoologica - Special Collections University of Amsterdam - (white background).jpg|50 px]]
               |2={{Clade
                  |1=[[Antilocapridae]][[File:Antilocapra white background.jpg|50 px]]
                  |2={{Clade
                     |1=[[Giraffidae]][[File:Giraffa camelopardalis Brockhaus white background.jpg|50 px]]
                     |2={{Clade
                        |1=[[Cervidae]][[File:The deer of all lands (1898) Hangul white background.png|50 px]]
                        |2={{Clade
                           |1=[[Moschidae]][[File:Moschus chrysogaster white background.jpg|50 px]]
                           |2=[[Bovidae]][[File:Birds and nature (1901) (14562088237) white background.jpg|50 px]]
                           }}
                        }}
                     }}
                  }}
               }}
            |label2=[[Whippomorpha]]
            |2={{Clade
               |1=[[Hippopotamidae]][[File:Voyage en Abyssinie Plate 2 (white background).jpg|50 px]]
               |2={{Clade 
                  |label1=[[Cetacea]]
                  |1={{Clade 
                     |label1=[[Mysticeti]]
                     |1={{Clade
                        |1=[[Balaenidae]][[File:Balaena mysticetus NOAA.jpg|50 px]]
                        |2={{Clade
                           |1=[[Cetotheriidae]][[File:Caperea marginata 3 flipped.jpg|50 px]]
                           |2=[[Balaenopteridae]] [[File:Megaptera novaeangliae NOAA.jpg|50 px]]
                           }}
                        }}
                     |label2=[[Odontoceti]]
                     |2={{Clade
                        |1={{Clade
                           |1=[[Physeteridae]][[File:Physeter macrocephalus NOAA.jpg|50 px]]
                           |2=[[Kogiidae]][[File:Kogia_sima_(transparent_background).png|50 px]]
                           }}
                        |2={{Clade 
                           |1=[[Platanistidae]][[File:Ganges.png|50 px]]
                           |2={{Clade
                              |1=[[Ziphiidae]][[File:Ziphius cavirostris NOAA.jpg|50 px]]
                              |2={{Clade
                                 |1=†[[Lipotidae]][[File:Lipotes vexillifer.png|50 px]]
                                 |2={{Clade 
                                    |1={{Clade
                                       |1=[[La Plata dolphin|Pontoporiidae]][[File:Pontoporia blainvillei.jpg|50 px]]
                                       |2=[[Iniidae]][[File:Inia_geoffrensis.jpg|50 px]]
                                       }}
                                    |2={{Clade
                                       |1=[[Delphinidae]] [[File:Orcinus orca NOAA 2.jpg|50 px]]
                                       |2={{Clade
                                          |1=[[Phocoenidae]] [[File:Vaquita swimming through the void. (Phocoena Sinus).png|50 px]]
                                          |2=[[Monodontidae]] [[File:Delphinapterus leucas NOAA.jpg|50 px]]
                                          }}
                                       }}
                                    }}
                                 }}
                              }}
                           }}
                        }}
                     }}
                  }}
               }}
            }}
         }}
      }}
   }}
}}

==Evolutionary history==
[[File:Protungulatum.png|thumb|left|Speculative [[Paleoart|reconstruction]] of the controversial ''Protungulatum'']]
[[File:Cladogram of Cetacea within Artiodactyla.png|thumb|upright=1.7|[[Cladogram]] showing relationships within Euungulata<ref name=Spauldingetal2009/>]]

[[Perissodactyla]] and [[Artiodactyla]]  include the majority of large land mammals. These two groups first appeared during the late [[Paleocene]], rapidly spreading to a wide variety of species on numerous continents, and have developed in parallel since that time. Some scientists believed that modern ungulates were descended from an [[evolutionary grade]] of mammals known as the [[condylarth]]s.<ref name=RoseArchaicUng>{{cite book|last=Rose|first=Kenneth D.|title=The beginning of the Age of Mammals|year=2006|publisher=Johns Hopkins University Press|location=Baltimore|isbn=9780801892219|chapter=Archaic Ungulates}}</ref> The earliest known member of this group may have been the tiny ''[[Protungulatum]]'', a mammal that co-existed with the last of non-avian [[dinosaur]]s 66&nbsp;million years ago.<ref>Jehle, Martin [http://www.paleocene-mammals.de/condylarths.htm#Arctocyonidae "Condylarths: Archaic hoofed mammals"] in ''Paleocene mammals of the world''</ref> However, many authorities do not consider it a true placental, let alone an ungulate.<ref>{{cite journal | last1 = Archibald | first1 = J. David | last2 = Zhang | first2 = Yue | last3 = Harper | first3 = Tony | last4 = Cifelli | first4 = Richard L. | year = 2011 | title = Protungulatum, Confirmed Cretaceous Occurrence of an Otherwise Paleocene Eutherian (Placental?) Mammal | journal = Journal of Mammalian Evolution | volume = 18| issue = 3| pages = 153–161| doi = 10.1007/s10914-011-9162-1 | s2cid = 16724836 }}</ref> The enigmatic [[dinocerata]]ns were among the first large herbivorous mammals, although their exact relationship with other mammals is still debated with one of the theories being that they might just be distant relatives to living ungulates; the most recent study recovers them as within the true ungulate assemblage, closest to ''[[Carodnia]]''.<ref name="Berger-Benjamin">{{cite conference |last=Burger |first=Benjamin J. |date=15 October 2015 |title=The Systematic Position of the Saber-Toothed and Horned Giants of the Eocene: The Uintatheres (Order Dinocerata) |url=http://www.benjamin-burger.org/wp-content/uploads/2019/12/SVP-Poster-Ben-Burger-2015.pdf |location=Dallas |conference=Society of Vertebrate Paleontology 75th Annual Meeting |access-date=20 February 2020 }} [http://vertpaleo.org/PDFS/SVP-2015-Program-and-Abstract-Book-9-22-2015.aspx Conference abstract (p. 99)] {{Webarchive|url=https://web.archive.org/web/20191224042705/http://vertpaleo.org/PDFS/SVP-2015-Program-and-Abstract-Book-9-22-2015.aspx |date=2019-12-24 }}. Explanation and conclusions: {{YouTube|B6lmLo14Cc0|Episode 17: Systematic position of the Uintatheres (Order Dinocerata)}}.</ref>

In Australia, the recently-extinct [[marsupial]] ''[[Chaeropus]]'' ("pig-footed bandicoot") also developed hooves similar to those of artiodactyls,<ref>{{cite journal|last1=Sánchez-Villagra|first1=Marcelo R|year=2013|title=Why were There Fewer Marsupials than Placentals? On the Relevance of Geography and Physiology to Evolutionary Patterns of Mammalian Diversity and Disparity|url=https://www.zora.uzh.ch/id/eprint/71489/10/ZORA_NL_71489.pdf|journal=Journal of Mammalian Evolution|volume=20|issue=4|pages=279–290|doi=10.1007/s10914-012-9220-3|s2cid=18789008}}</ref> an example of [[convergent evolution]].

===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.

===Artiodactyl evolution===
[[File:Arctocyon DB.jpg|thumb|''[[Arctocyon]]'', an [[Arctocyonidae|arctocyonid]]]]
The artiodactyls were thought to have evolved from a small group of condylarths, [[Arctocyonidae]], which were unspecialized, superficially raccoon-like to bear-like omnivores from the Early [[Paleocene]] (about 65 to 60&nbsp;million years ago). They had relatively short limbs lacking specializations associated with their relatives (e.g. reduced side digits, fused bones, and hooves),<ref name="Jehle-Condylarths">Jehle, Martin [http://www.paleocene-mammals.de/condylarths.htm#Phenacodontidae "Condylarths: Archaic hoofed mammals"] in ''Paleocene mammals of the world''</ref> and long, heavy tails. Their primitive anatomy makes it unlikely that they were able to run down prey, but with their powerful proportions, claws, and long canines, they may have been able to overpower smaller animals in surprise attacks.<ref name="Jehle-Condylarths"/> Evidently these mammals soon evolved into two separate lineages: the [[mesonychia]]ns and the artiodactyls.

[[File:Anoplotherium commune.jpg|thumb|left|Skeleton of ''[[Anoplotherium commune]]'', an early artiodactyl with unusual features such as a long tail]]
The first artiodactyls looked like today's [[chevrotain]]s or pigs: small, short-legged creatures that ate [[leaves]] and the soft parts of [[plants]]. By the Late Eocene (46&nbsp;million years ago), the three modern suborders had already developed: [[Suina]] (the [[pig]] group); [[Tylopoda]] (the [[camel]] group); and [[Ruminantia]] (the [[goat]] and [[cattle]] group). Nevertheless, artiodactyls were far from dominant at that time: the perissodactyls were much more successful and far more numerous. Artiodactyls survived in niche roles, usually occupying marginal [[habitat (ecology)|habitats]], and it is presumably at that time that they developed their complex [[digestive system]]s, which allowed them to survive on lower-grade food. While most artiodactyls were taking over the niches left behind by several extinct perissodactyls, one lineage of artiodactyls began to venture out into the seas.

====Cetacean evolution====
{{See also|Evolution of cetaceans}}
[[File:Ambulocetus natans.jpg|thumb|Skeleton of ''[[Ambulocetus natans]]'', a stem whale]]
The traditional theory of cetacean evolution was that cetaceans were related to the [[Mesonychia|mesonychian]]. These animals had unusual triangular teeth very similar to those of primitive cetaceans.  This is why scientists long believed that cetaceans evolved from a form of mesonychian. Today, many scientists believe cetaceans evolved from the same stock that gave rise to hippopotamuses. This hypothesized ancestral group likely split into two branches around {{mya|54|million years ago}}.<ref name="Genomes" /> One branch would [[Evolution of cetaceans|evolve into cetaceans]], possibly beginning about {{mya|52|million years ago}} with the proto-whale ''[[Pakicetus]]'' and other early cetacean ancestors collectively known as [[Archaeoceti]], which eventually underwent [[aquatic adaptation]] into the completely aquatic [[cetacea]]ns.<ref name="Cetartiodactyla">{{cite journal |last=Boisserie |first=Jean-Renaud |author2=Lihoreau, F. |author3=Brunet, M. |date=February 2005 |title= The position of Hippopotamidae within Cetartiodactyla |journal= [[Proceedings of the National Academy of Sciences]] |volume= 102 |issue= 5 |pages= 1537–1541|doi= 10.1073/pnas.0409518102 |pmc=547867|bibcode = 2005PNAS..102.1537B |pmid= 15677331 |doi-access=free }}</ref> The other branch became the [[anthracotheriidae|anthracotheres]], a large family of four-legged beasts, the earliest of whom in the late [[Eocene]] would have resembled skinny hippopotamuses with comparatively small and narrow heads. All branches of the anthracotheres, except that which evolved into [[Hippopotamidae]], became extinct during the [[Pliocene]] without leaving any descendants.<ref name="ScienceNews">{{Cite web | title = Scientists find missing link between the dolphin, whale and its closest relative, the hippo | date = 2005-01-25 | access-date = 2007-06-18 | url = http://www.sciencenewsdaily.org/story-2806.html | work = Science News Daily | url-status = dead | archive-url = https://web.archive.org/web/20070304214747/http://www.sciencenewsdaily.org/story-2806.html | archive-date = 2007-03-04 }}</ref>

The family [[Raoellidae]] is said to be the closest artiodactyl family to the cetaceans.<ref>{{cite journal |last1=Thewissen |first1=J. G. M. |year=2007 |title=Whales originated from aquatic artiodactyls in the Eocene epoch of India |journal=Nature |volume=450 |issue=7173 |pages=1190–1194 |doi=10.1038/nature06343 |url= http://repository.ias.ac.in/4642/1/316.pdf|pmid=18097400 |last2=Cooper |first2=LN |last3=Clementz |first3=MT |last4=Bajpai |first4=S|author4-link=Sunil Bajpai |last5=Tiwari |first5=BN |bibcode=2007Natur.450.1190T|s2cid=4416444 }}</ref><ref>{{cite magazine
|url=http://www.sciam.com/article.cfm?id=closest-whale-cousin
|title=Closest Whale Cousin—A Fox-Size Deer? Researchers split on closest evolutionary kin to whales and dolphins
|first=JR
|last=Minkel 
|magazine=Scientific American
|date=2007-12-19}}</ref> Consequentially, new theories in cetacean evolution hypothesize that whales and their ancestors escaped predation, not competition, by slowly adapting to the ocean.<ref name=GuardianIndohyus>{{cite news |url=https://www.theguardian.com/science/2007/dec/19/whale.deer?gusrc=rss&feed=networkfront |title=Whales may be descended from a small deer-like animal  |access-date=2007-12-21 |author= Sample, Ian|date=December 19, 2007|work=[[Guardian Unlimited]] |location=London}}</ref><ref name=TheLoom>{{cite web |url=http://scienceblogs.com/loom/2007/12/19/whales_from_so_humble_a_beginn.php |title=The Loom : Whales: From So Humble A Beginning... |access-date=2007-12-21 |author=Zimmer, Carl |author-link=Carl Zimmer |date=December 19, 2007 |publisher=[[ScienceBlogs]] |archive-date=2007-12-21 |archive-url=https://web.archive.org/web/20071221103928/http://scienceblogs.com/loom/2007/12/19/whales_from_so_humble_a_beginn.php |url-status=dead }}</ref><ref name=PharyngulaIndohyus>{{cite web |url=http://scienceblogs.com/pharyngula/2007/12/indohyus.php |title=Pharyngula: Indohyus |access-date=2007-12-21 |author=Myers, P.Z. |author-link=PZ Myers |date=December 19, 2007 |work=[[Pharyngula (blog)|Pharyngula]] |publisher=[[ScienceBlogs]] |archive-date=2007-12-20 |archive-url=https://web.archive.org/web/20071220115757/http://scienceblogs.com/pharyngula/2007/12/indohyus.php |url-status=dead }}</ref>

===Mesonychian evolution===
[[File:Mesonyx.jpg|thumb|left|Restoration of ''Mesonyx'']]
Mesonychians were depicted as "wolves on hooves" and were the first major mammalian predators, appearing in the Paleocene.<ref name="Jehle">Jehle, Martin [http://www.paleocene-mammals.de/predators.htm#Carnivorous "Carnivores, creodonts and carnivorous ungulates: Mammals become predators"] in ''Paleocene mammals of the world''</ref>  Early mesonychians had five digits on their feet, which probably rested flat on the ground during walking ([[plantigrade]] locomotion), but later mesonychians had four digits that ended in tiny hooves on all of their toes and were increasingly well adapted to running. Like running members of the even-toed ungulates, mesonychians (''Pachyaena'', for example) walked on their digits ([[digitigrade]] locomotion).<ref name="Jehle"/> Mesonychians fared very poorly at the close of the Eocene epoch, with only one genus, ''[[Mongolestes]]'',<ref name=Jin05>{{cite journal|author=Jin, X. |year=2005 |title=Mesonychids from Lushi Basin, Henan Province, China ''(in Chinese with English summary)'' |journal=Vertebrata PalAsiatica |volume=43 |issue=2 |pages=151–164 |url=http://www.ivpp.ac.cn/pdf/magazine308.pdf }}{{dead link|date=June 2016|bot=medic}}{{cbignore|bot=medic}}</ref> surviving into the Early [[Oligocene]] epoch, as the climate changed and fierce competition arose from the better adapted [[creodont]]s.

==Characteristics==
[[Image:Horse anatomy.svg|thumb|upright=1.3|Skeleton of a horse]]
Ungulates were in high diversity in response to [[sexual selection]] and [[ecological]] events; most ungulates lack a [[clavicle|collar bone]].<ref>''The Illustrated Encyclopedia of the Animal Kingdom''. p. 7</ref> Terrestrial ungulates were for the most part herbivores, with some of them being [[grazing|grazers]]. However, there were exceptions to this as pigs, peccaries, hippos and [[duiker]]s were known to have an omnivorous diet. Some cetaceans were the only modern ungulates that were carnivores; baleen whales consume significantly smaller animals in relation to their body size, such as small species of fish and [[krill]]; toothed whales, depending on the species, can consume a wide range of species: [[squid]], fish, [[shark]]s, and other species of mammals such as [[Pinniped|seals]] and other whales. In terms of ecosystem ungulates have colonized all corners of the planet, from [[mountain]]s to the [[ocean depths]]; [[grassland]]s to [[desert]]s and some have been domesticated by [[human]]s.

===Anatomy===
Ungulates have developed specialized adaptations, especially in the areas of cranial appendages, dentition, and leg morphology including the modification of the [[talus bone|astragalus]] (one of the ankle bones at the end of the lower leg) with a short, robust head.

====Hooves====
{{See also|Hoof}}
[[Image:Capreolus capreolus cloven hoof.jpg|right|thumbnail|Cloven hooves of [[roe deer]] (''Capreolus capreolus''), with dewclaws]] 
The hoof is the tip of the [[toe]] of an ungulate [[mammal]], strengthened by a thick horny ([[keratin]]) covering. The hoof consists of a hard or rubbery sole, and a hard wall formed by a thick [[Nail (anatomy)|nail]] rolled around the tip of the toe. Both the sole and the edge of the hoof wall normally bear the weight of the animal. Hooves grow continuously, and are constantly worn down by use. In most modern ungulates, the [[Radius (bone)|radius]] and [[ulna]] are fused along the length of the forelimb; early ungulates, such as the [[Arctocyonidae|arctocyonids]], did not share this unique skeletal structure.<ref>Janis, Christine M.; Scott, Kathleen M. and Jacobs, Louis L. (1998) ''Evolution of Tertiary Mammals of North America'', Volume 1. Cambridge: Cambridge University Press. pp. 322-23. {{ISBN|9780521355193}}</ref> The fusion of the radius and ulna prevents an ungulate from rotating its forelimb. Since this skeletal structure has no specific function in ungulates, it is considered a homologous characteristic that ungulates share with other mammals. This trait would have been passed down from a common ancestor. While the two orders of ungulates colloquial names were based on the number of toes of their members ("odd-toed" for the perissodactyls and "even-toed" for the terrestrial artiodactyls), it is not an accurate reason they were grouped. Tapirs have four toes in the front, yet they were members of the "odd-toed" order; peccaries and modern cetaceans were members of the "even-toed" order, yet peccaries have three toes in the front and whales were an extreme example as they have flippers instead of hooves. Scientists had classified them according to the distribution of their weight to their toes.

Perissodactyls have a mesaxonic foot, meaning that the weight is distributed on the third toe on all legs thanks to the plane symmetry of their feet. There has been a reduction of toes from the common ancestor, with the classic example being horses with their single hooves. In consequence, there was an alternative name for the perissodactyls the nearly obsolete Mesaxonia. Perissodactyls were not the only lineage of mammals to have evolved this trait; the [[Meridiungulata|meridiungulates]] have evolved mesaxonic feet numerous times.

Terrestrial artiodactyls have a paraxonic foot, meaning that the weight is distributed on the third and the fourth toe on all legs. The majority of these mammals have cloven hooves, with two smaller ones known as the [[dewclaws]] that were located further up on the leg. The earliest cetaceans (the [[archaeocetes]]), also had this characteristic in the addition of also having both an [[Astragalus (bone)|astragalus]] and [[cuboid bone]] in the ankle, which were further diagnostic traits of artiodactyls.<ref>{{Cite journal 
| doi = 10.1126/science.1063902 
|date=Sep 2001 
|author1=Gingerich, P.D. |author2=ul Haq, M. |author3=Zalmout, I.S. |author4=Khan, I.H. |author5=Malkani, M.S. | title = Origin of whales from early artiodactyls: hands and feet of Eocene Protocetidae from Pakistan 
| volume = 293 
| issue = 5538 
| pages = 2239–42 
| pmid = 11567134 
| journal = Science
| bibcode=2001Sci...293.2239G
|s2cid=21441797 
| doi-access=free 
}}</ref>

[[File:White-sided dolphin.jpg|thumb|right|[[Pacific white-sided dolphin]] skeleton (missing [[pelvic bones]]), on exhibit at [[The Museum of Osteology]], [[Oklahoma City, Oklahoma]]]]
In modern cetaceans, the front limbs had become [[pectoral fins]] and the hind parts were internal and reduced. Occasionally, the genes that code for longer extremities cause a modern cetacean to develop miniature legs (known as [[atavism]]). The main method of moving is an up-and-down motion with the tail fin, called the [[:wiktionary:fluke|fluke]], which is used for [[Animal locomotion|propulsion]], while the pectoral fins together with the entire tail section provide directional control. All modern cetaceans still retain their digits despite the external appearance suggesting otherwise.

====Teeth====
Most ungulates have developed reduced [[canine teeth]] and specialized [[molar (tooth)|molars]], including bunodont (low, rounded cusps) and [[hypsodont]] (high crowned) teeth. The development of hypsodonty has been of particular interest as this adaptation was strongly associated with the spread of grasslands during the [[Miocene]] about 25&nbsp;million years ago. As forest biomes declined, grasslands spread, opening new [[Ecological niche|niches]] for mammals. Many ungulates switched from browsing diets to grazing diets, and possibly driven by abrasive silica in grass, hypsodonty became common. However, recent evidence ties the evolution of hypsodonty to open, gritty habitats and not the grass itself. This is termed the [[Grit, not grass hypothesis]].<ref>{{cite journal | last1 = Jardine | first1 = Phillip E. | last2 = Janis | first2 = Christine M. | last3 = Sahney | first3 = Sarda | last4 = Benton | first4 = Michael J. | year = 2012 | title = Grit not grass: Concordant patterns of early origin of hypsodonty in Great Plains ungulates and Glires | doi = 10.1016/j.palaeo.2012.09.001 | journal = Palaeogeography, Palaeoclimatology, Palaeoecology | volume = 365–366 | pages = 1–10 | bibcode = 2012PPP...365....1J }}</ref>

Some ungulates completely lack upper incisors and instead have a [[dental pad]] to assist in browsing.<ref name="2001Rouge">{{cite web | title = Dental Anatomy of Ruminants | last = Rouge | first = Melissa | year = 2001 | publisher = Colorado State University | url = http://www.vivo.colostate.edu/hbooks/pathphys/digestion/pregastric/cowpage.html | access-date = 5 May 2010 | archive-date = 28 September 2011 | archive-url = https://web.archive.org/web/20110928131653/http://www.vivo.colostate.edu/hbooks/pathphys/digestion/pregastric/cowpage.html | url-status = dead }}</ref><ref name="WonderQuest">{{cite web | publisher = WonderQuest | title = Toothless cud chewers, To see ourselves as others see us... | url = http://www.wonderquest.com/cows-teeth-mirrors.htm | access-date = 5 May 2010}}</ref> It can be found in camels, ruminants, and some toothed whales; modern baleen whales were remarkable in that they have [[baleen]] instead to filter out the krill from the water. On the other spectrum teeth have been evolved as weapons or sexual display seen in pigs and peccaries, some species of deer, musk deer, hippopotamuses, beaked whales and the Narwhal, with its long canine tooth.<ref name="Nweeia et al.">{{cite journal|last1=Nweeia|first1=Martin T.|title=Vestigial tooth anatomy and tusk nomenclature for ''Monodon monoceros''|journal=The Anatomical Record|year=2012|doi=10.1002/ar.22449|pmid=22467529|volume=295|issue=6|pages=1006–16|first2=Frederick C.|last2=Nweeia|first3=Peter V.|last3=Hauschka|first4=Ethan|last4=Tyler|first5=James G.|last5=Mead|first6=Charles W.|last6=Potter|first7=David P.|last7=Angnatsiak|first8=Pierre R.|last8=Richard|first9=Jack R.|last9=Orr|first10=Sandie R.|last10=Black|s2cid=22907605|display-authors=etal|doi-access=free}}</ref>

====Cranial appendages====
{{See also|Horn (anatomy)|Ossicone|Antler}}
[[File:Red deer stag velvet.jpg|thumb|upright|[[velvet antler|Velvet]] covers a growing antler and provides it with blood, supplying oxygen and nutrients.]]

Ungulates have evolved a variety of cranial appendages that can be found in [[Pecora|cervoids]] (with the exception of musk deer). In oxen and antelope, the size and shape of the [[horn (anatomy)|horns]] varies greatly but the basic structure is always a pair of simple bony protrusions without branches, often having a spiral, twisted, or fluted form, each covered in a permanent sheath of [[keratin]]. The unique horn structure is the only unambiguous morphological feature of bovids that distinguishes them from other [[pecorans]].<ref>{{cite journal |last1=Bibi |first1=F. |last2=Bukhsianidze |first2=M. |last3=Gentry |first3=A. |last4=Geraads |first4=D. |last5=Kostopoulos |first5=D. |last6=Vrba |first6=E. |year=2009 |title=The fossil record and evolution of Bovidae: State of the field |url=http://palaeo-electronica.org/2009_3/169/index.html |journal=Palaeontologia Electronica |volume=12 |issue=3 |pages=10A}}</ref><ref>{{cite journal|last=Gatesy|first=J.|author2=Yelon, D., DeSalle, R., Vrba, E. |year=1992|title=Phylogeny of the Bovidae (Artiodactyla, Mammalia), Based on Mitochondrial Ribosomal DNA Sequences|journal=Mol. Biol. Evol.|volume=9|issue=3|pages=433–446|pmid=1584013|doi=10.1093/oxfordjournals.molbev.a040734|doi-access=free}}</ref> Male horn development has been linked to sexual selection,<ref name=BroJ>{{cite journal|doi=10.1111/j.1558-5646.2007.00111.x|last=Bro-Jørgensen|first=J.|year=2007|title=The intensity of sexual selection predicts weapon size in male bovids|journal=Evolution|volume=61|issue=6|pages=1316–1326|pmid=17542842|s2cid=24278541|doi-access=free}}</ref><ref>{{cite journal|last=Ezenwa|first=V.|author2=Jolles, A. |year=2008|title=Horns honestly advertise parasite infection in male and female African buffalo|journal=Animal Behaviour|doi=10.1016/j.anbehav.2007.12.013|volume=75|pages=2013–2021|issue=6|s2cid=49240459}}</ref> while the presence of horns in females is likely due to natural selection.<ref name=BroJ/><ref name=Stankowich>{{cite journal|last=Stankowich|first=T.|author2=Caro, T. |author2-link=Tim Caro |year=2009|title=Evolution of weaponry in female bovids|journal=[[Proceedings of the Royal Society B]]|pmid=19759035|doi=10.1098/rspb.2009.1256|volume=276|issue=1677|pages=4329–34|pmc=2817105}}</ref> The horns of females are usually smaller than those of males and are sometimes of a different shape. The horns of female bovids are thought to have evolved for defense against [[predator]]s or to express territoriality, as nonterritorial females, which are able to use [[crypsis]] for predator defense, often lack horns.<ref name=Stankowich/>

Rhinoceros horns, unlike those of other horned mammals, consist only of keratin. These horns rest on the nasal ridge of the animal's skull.

[[Antler]]s are unique to cervids and found mostly on males: the only cervid females with antlers are [[reindeer|caribou and reindeer]], whose antlers are normally smaller than males'. Nevertheless, fertile [[wiktionary:doe#English|does]] of other species of deer have the capacity to produce antlers on occasion, usually due to increased testosterone levels.<ref>[http://www.das.psu.edu/research-extension/deer/photos/antlered-doe Antlered Doe] {{webarchive|url=https://web.archive.org/web/20120229040529/http://www.das.psu.edu/research-extension/deer/photos/antlered-doe |date=2012-02-29 }}</ref> Each antler grows from an attachment point on the skull called a pedicle. While an antler is growing it is covered with highly [[Blood vessel|vascular]] [[skin]] called velvet, which supplies oxygen and nutrients to the growing bone.<ref name=Hall>{{Cite book | last = Hall | first = Brian K. | year = 2005 | title = Bones and Cartilage: Developmental and Evolutionary Skeletal Biology | publisher = Academic Press | chapter = Antlers | pages = 103–114 | isbn = 978-0-12-319060-4 | chapter-url = https://books.google.com/books?id=y-RWPGDONlIC&pg=PA103 | access-date = 2010-11-08 }}</ref>  Antlers are considered one of the most exaggerated cases of male secondary sexual traits in the animal kingdom,<ref name="Malo">{{cite journal | last1 = Malo | first1 = A. F. | last2 = Roldan | first2 = E. R. S. | last3 = Garde | first3 = J. | last4 = Soler | first4 = A. J. | last5 = Gomendio | first5 = M. | year = 2005 | title = Antlers honestly advertise sperm production and quality | journal = Proceedings of the Royal Society B | volume = 272 | issue = 1559| pages = 149–157 | doi=10.1098/rspb.2004.2933 | pmid=15695205 | pmc=1634960}}</ref> and grow faster than any other mammal bone.<ref name=W&H>{{Cite book | last1 = Whitaker | first1 = John O. | last2 = Hamilton | first2 = William J. Jr. | year = 1998 | title = Mammals of the Eastern United States | publisher = Cornell University Press | page = 517 | isbn = 978-0-8014-3475-4 | url = https://books.google.com/books?id=5fVymWAez-YC&pg=PA517 | access-date = 2010-11-08 }}</ref>  Growth occurs at the tip, initially as [[cartilage]] that is then mineralized to become bone. Once the antler has achieved its full size, the velvet is lost and the antler's bone dies. This dead bone structure is the mature antler. In most cases, the bone at the base is destroyed by [[osteoclast]]s and the antlers eventually fall off.<ref name=Hall/> As a result of their fast growth rate antlers place a substantial nutritional demand on deer; they thus can constitute an honest signal of metabolic efficiency and food gathering capability.<ref name="Ditchkoff">{{cite journal | last1 = Ditchkoff | first1 = S. S. | last2 = Lochmiller | first2 = R. L. | last3 = Masters | first3 = R. E. | last4 = Hoofer | first4 = S. R. | last5 = Den Bussche | first5 = R. A. Van | year = 2001 | title = Major-histocompatibility-complex-associated variation in secondary sexual traits of white-tailed deer (Odocoileus virginianus): evidence for good-genes advertisement | journal = Evolution | volume = 55 | issue = 3| pages = 616–625 | doi=10.1111/j.0014-3820.2001.tb00794.x | pmid=11327168| s2cid = 10418779 | doi-access = free }}</ref>

[[Ossicone]]s are horn-like (or antler-like) protuberances found on the heads of giraffes and male [[okapi]]s. They are similar to the horns of [[antelope]]s and [[cattle]] save that they are derived from ossified [[cartilage]],<ref>"The Nashville Zoo at Grassmere - Animals :: Masai Giraffe". The Nashville Zoo at Grassmere, n.d. Web. 15 Feb. 2010. {{cite web|title=The Nashville Zoo at Grassmere - Animals :: Masai Giraffe|url=http://www.nashvillezoo.org/animals_detail.asp?animalID=12|url-status=dead|archive-url=https://web.archive.org/web/20101220142807/http://nashvillezoo.org/animals_detail.asp?animalID=12|archive-date=2010-12-20|access-date=2013-02-10}}</ref> and that the ossicones remain covered in [[skin]] and [[fur]] rather than horn.

[[Pronghorn]] cranial appendages are unique. Each "horn" of the pronghorn is composed of a slender, laterally flattened blade of bone that grows from the frontal bones of the skull, forming a permanent core. As in the Giraffidae, skin covers the bony cores, but in the pronghorn it develops into a keratinous sheath that is shed and regrown on an annual basis. Unlike the horns of the family Bovidae, the horn sheaths of the pronghorn are branched, each sheath possessing a forward-pointing tine (hence the name pronghorn). The horns of males are well developed.

==See also==
* [[Altungulata]]

== References ==
{{Reflist}}

== External links ==
{{Wiktionary}}
* [https://web.archive.org/web/20070202174629/http://www.ultimateungulate.com/ Your Guide to the World's Hoofed Mammals] – The Ultimate Ungulate Page
* {{Cite EB1911|wstitle=Ungulata|short=x}}

{{Locomotion}}
{{Taxonbar|from=Q1231177}}
{{Authority control}}

[[Category:Ungulates| ]]
[[Category:Extant Paleocene first appearances]]
[[Category:Taxa named by Carl Linnaeus]]