Editing Artiodactyl (section)

==Taxonomy and phylogeny==
[[File:Thomas Herbert Maguire - Richard Owen 1850.png|thumb|[[Richard Owen]] coined the term "even-toed ungulate".|alt=Portrait of Richard Owen]]

The classification of artiodactyls was hotly debated because ocean-dwelling [[cetacea]]ns evolved from land-dwelling even-toed ungulates. Some [[semiaquatic]] even-toed ungulates ([[hippopotamus]]es) are more closely related to ocean-dwelling cetaceans than to other even-toed ungulates.<ref name="montgelard97"/>

Phylogenetic classification only recognizes [[monophyletic]] taxa; that is, groups that descend from a common ancestor and include all of its descendants. To address this problem, the traditional order Artiodactyla and infraorder [[Cetacea]] are sometimes subsumed into the more inclusive Cetartiodactyla taxon.<ref name="montgelard97">{{Cite journal |last1=Montgelard |first1=Claudine |last2=Catzeflis |first2=Francois M. |last3=Douzery |first3=Emmanuel |year=1997 |title=Phylogenetic relationships of artiodactyls and cetaceans as deduced from the comparison of cytochrome b and 12S rRNA mitochondrial sequences |journal=Molecular Biology and Evolution |volume=14 |issue=5 |pages=550–559 |doi=10.1093/oxfordjournals.molbev.a025792 |pmid=9159933 |doi-access=}}</ref> An alternative approach is to include both land-dwelling even-toed ungulates and ocean-dwelling cetaceans in a revised Artiodactyla taxon.<ref name="spaulding2009" />

===Classification===
{{main|List of artiodactyls}}
* '''Order Artiodactyla'''/'''Clade Cetartiodactyla'''<ref name="spaulding2009">{{Cite journal |last1=Spaulding |first1=M |last2=O'Leary |first2=MA |last3=Gatesy |first3=J |year=2009 |editor-last=Farke |editor-first=Andrew Allen |title=Relationships of Cetacea (Artiodactyla) Among Mammals: Increased Taxon Sampling Alters Interpretations of Key Fossils and Character Evolution |journal=PLOS ONE |volume=4 |issue=9 |pages=e7062 |bibcode=2009PLoSO...4.7062S |doi=10.1371/journal.pone.0007062 |pmc=2740860 |pmid=19774069 |doi-access=free}}</ref><ref>{{Cite book |last1=Groves |first1=Colin P. |title=Ungulate Taxonomy |last2=Grubb |first2=Peter |date=2011 |publisher=Johns Hopkins University Press |isbn=978-1-4214-0093-8 |location=Baltimore, Maryland |page=25}}</ref>
** Family {{Abbr|†|Extinct}}[[Diacodexeidae]]
** Family {{Abbr|†|Extinct}}[[Amphimerycidae]]
** Family {{Abbr|†|Extinct}}[[Robiacinidae]]
** Family {{Abbr|†|Extinct}}[[Cainotheriidae]]
**'''Suborder [[Tylopoda]]'''
*** Family {{Abbr|†|Extinct}}[[Anoplotheriidae]]?
*** Family {{Abbr|†|Extinct}}[[Merycoidodontidae]]
*** Family {{Abbr|†|Extinct}}[[Agriochoeridae]]
*** Family [[Camelidae]]: [[camel]]s, [[llama]]s, [[alpaca]]s, [[vicuña]]s, and [[guanaco]]s (7 extant and 13 extinct species)
*** Family {{Abbr|†|Extinct}}[[Oromerycidae]]
*** Family {{Abbr|†|Extinct}}[[Xiphodontidae]]?
*** Family {{Abbr|†|Extinct}}[[Protoceratidae]]?
** '''Clade [[Artiofabula]]'''
***'''Suborder [[Suina]]'''
**** Family [[Suidae]]: pigs (19 species)
**** Family [[Tayassuidae]]: peccaries (4 species)
**** Family {{Abbr|†|Extinct}}[[Sanitheriidae]]
****Family {{Abbr|†|Extinct}}[[Doliochoeridae]]
*** '''Clade [[Cetruminantia]]'''
****'''Clade [[Cetancodontamorpha]]'''
***** Genus {{Abbr|†|Extinct}}''[[Andrewsarchus]]''?
***** Family {{Abbr|†|Extinct}}[[Entelodontidae]]
***** '''Suborder [[Whippomorpha]]'''
****** Family {{Abbr|†|Extinct}}[[Raoellidae]]
****** Superfamily [[Dichobunoidea]] – paraphyletic to Cetacea and Raoellidae
******* Family {{Abbr|†|Extinct}}[[Dichobunidae]]
******* Family {{Abbr|†|Extinct}}[[Helohyidae]]
******* Family {{Abbr|†|Extinct}}[[Choeropotamidae]]
******* Family {{Abbr|†|Extinct}}[[Cebochoeridae]] (Family contains [[Cebochoerus]])
******* Family {{Abbr|†|Extinct}}[[Mixtotheriidae]]
****** '''Infraorder [[Ancodonta]]'''
******* Family {{Abbr|†|Extinct}}[[Anthracotheriidae]] – paraphyletic to Hippopotamidae
******* Family [[Hippopotamidae]]: hippos (two species)
****** '''Infraorder [[Cetacea]]''': whales (about 90 species)
*******'''Parvorder {{Abbr|†|Extinct}}[[Archaeoceti]]'''
******** Family {{Abbr|†|Extinct}}[[Pakicetidae]]
******** Family {{Abbr|†|Extinct}}[[Ambulocetidae]]
******** Family {{Abbr|†|Extinct}}[[Remingtonocetidae]]
******** Family {{Abbr|†|Extinct}}[[Basilosauridae]]
******* '''Clade [[Neoceti]]'''
******** '''Parvorder [[Mysticeti]]''': baleen whales
********* Superfamily Balaenoidea: [[right whale]]s
********** Family [[Balaenidae]]: greater [[right whale]]s (four species)
********** Family [[Cetotheriidae]]: [[pygmy right whale]] (one species)
********* Superfamily Balaenopteroidea: large [[baleen whale]]s
********** Family [[Balaenopteridae]]: [[Balaenoptera|slender-back rorquals]] and [[humpback whale]] (eight species)
********** Family [[Eschrichtiidae]]: [[gray whale]] (one species)
******** '''Parvorder [[Odontoceti]]''': toothed whales
********* Superfamily [[Delphinoidea]]: [[oceanic dolphin]]s, [[porpoise]]s, and others
********** Family [[Delphinidae]]: [[Oceanic dolphin|oceanic true dolphins]] (38 species)
********** Family [[Monodontidae]]: [[Monodontidae|Arctic whales]]; [[narwhal]] and [[Beluga whale|beluga]] (two species)
********** Family [[Phocoenidae]]: [[porpoise]]s (six species)
********* Superfamily [[Physeteroidea]]: [[Physeteroidea|sperm whales]]
********** Family [[Kogiidae]]: [[Kogiidae|lesser sperm whales]] (two species)
********** Family [[Physeteridae]]: [[sperm whale]] (one species)
********* Superfamily [[Platanistoidea]]: [[river dolphin]]s
********** Family [[Iniidae]]: [[Iniidae|South American river dolphins]] (two species)
********** Family [[Lipotidae]]: [[Chinese river dolphin]] (one species, possibly extinct)
********** Family [[Platanistidae]]: [[South Asian river dolphin]] (one species)
********** Family [[Pontoporiidae]]: [[La Plata dolphin]] (one species)
********* Superfamily Ziphioidea
********** Family [[Ziphiidae]]: [[beaked whale]]s (22 species)
**** '''Total-group Ruminantia'''
***** '''Suborder [[Ruminantia]]'''
****** '''Infraorder [[Tragulina]]'''
******* Family {{Abbr|†|Extinct}}[[Leptomerycidae]]
******* Family {{Abbr|†|Extinct}}[[Hypertragulidae]]
******* Family {{Abbr|†|Extinct}}[[Praetragulidae]]
******* Family {{Abbr|†|Extinct}}[[Gelocidae]]
******* Family {{Abbr|†|Extinct}}[[Bachitheriidae]]
******* Family [[Tragulidae]]: chevrotains (ten species)
******* Family {{Abbr|†|Extinct}}[[Archaeomerycidae]]
******* Family {{Abbr|†|Extinct}}[[Lophiomerycidae]]
****** '''Infraorder [[Pecora]]'''
******* Family {{Abbr|†|Extinct}}[[Palaeomerycidae]]
******* Family {{Abbr|†|Extinct}}[[Dromomerycidae]]
******* Family [[Antilocapridae]]: [[pronghorn]] (one species)
******* Family {{Abbr|†|Extinct}}[[Climacoceratidae]]
******* Family [[Giraffidae]]: [[okapi]] and four species of [[giraffe]] (five species total)
******* Family {{Abbr|†|Extinct}}[[Hoplitomerycidae]]
******* Family [[Cervidae]]: [[deer]] (49 species)
******* Family [[Moschidae]]: [[musk deer]] (7 species)
******* Family [[Bovidae]]: [[Bos|cattle]], [[Bubalina|buffaloes]], [[Capra (genus)|goat]]s, [[Ovis|sheep]], [[antelope]]s, [[Caprinae|caprine]]s, and [[bison]] (135 species)

===Research history===
[[File:Humpback Whale underwater shot.jpg|thumb|Molecular and morphological studies confirmed that cetaceans are the closest living relatives of hippopotamuses.|alt=Humpback whale swimming under water]]

In the 1990s, biological [[systematics]] used not only morphology and fossils to classify organisms, but also [[molecular biology]]. Molecular biology involves sequencing an organism's DNA and RNA and comparing the sequence with that of other living beings—the more similar they are, the more closely they are related. Comparison of even-toed ungulate and cetaceans genetic material has shown that the closest living relatives of [[whale]]s and [[hippopotamus]]es is the paraphyletic group Artiodactyla.<ref name=Gatesy1996/><ref name=Amrine2003/>

Dan Graur and Desmond Higgins were among the first to come to this conclusion, and included a paper published in 1994.<ref>{{Cite journal |last1=Graur |first1=Dan |last2=Higgins |first2=Desmond G. |year=1994 |title=Molecular Evidence for the Inclusion of Cetaceans within the Order Artiodactyla |url=http://mbe.library.arizona.edu/data/1994/1103/3grau.pdf |url-status=dead |journal=Molecular Biology and Evolution |pages=357–364 |archive-url=https://web.archive.org/web/20160305180005/http://mbe.library.arizona.edu/data/1994/1103/3grau.pdf |archive-date=5 March 2016 |access-date=23 August 2015}}</ref> However, they did not recognize hippopotamuses and classified the [[ruminant]]s as the sister group of cetaceans. Subsequent studies established the close relationship between hippopotamuses and cetaceans; these studies were based on [[Casein|casein genes]],<ref name=Gatesy1996>{{Cite journal |last1=Gatesy |first1=John |last2=Hayashi |first2=Cheryl |last3=Cronin |first3=Mathew A. |last4=Arctander |first4=Peter |year=1996 |title=Evidence from milk casein genes that cetaceans are close relatives of hippopotamid artiodactyls |journal=Molecular Biology and Evolution |volume=13 |issue=7 |pages=954–963 |doi=10.1093/oxfordjournals.molbev.a025663 |pmid=8752004 |doi-access=free}}</ref> [[Short interspersed nuclear element|SINEs]],<ref>{{Cite journal |last=Shimamura |first=M. |year=1997 |title=Molecular evidence from retroposons that whales form a clade within even-toed ungulates |journal=Nature |volume=388 |issue=6643 |pages=666–670 |bibcode=1997Natur.388..666S |doi=10.1038/41759 |pmid=9262399 |doi-access=free |s2cid=4429657}} {{closed access}}</ref> [[fibrinogen]] sequences,<ref>{{Cite journal |last=Gatesy |first=John |year=1997 |title=More DNA Support for a Cetacea/Hippopotamidae Clade: The Blood-Clotting Protein Gene y-Fibrinogen |journal=Molecular Biology and Evolution |volume=14 |issue=5 |pages=537–543 |doi=10.1093/oxfordjournals.molbev.a025790 |pmid=9159931 |doi-access=free}}</ref> [[cytochrome]] and [[rRNA]] sequences,<ref name=montgelard97/><ref name="ReferenceA">{{Cite journal |last1=Agnarsson |first1=Ingi |last2=May-Collado |first2=Laura J. |year=2008 |title=The phylogeny of Cetartiodactyla: The importance of dense taxon sampling, missing data, and the remarkable promise of cytochrome b to provide reliable species-level phylogenies |url=https://www.researchgate.net/publication/5262443 |journal=Molecular Phylogenetics and Evolution |volume=48 |issue=3 |pages=964–85 |doi=10.1016/j.ympev.2008.05.046 |pmid=18590827 |bibcode=2008MolPE..48..964A |access-date=3 September 2018 |archive-date=4 September 2020 |archive-url=https://web.archive.org/web/20200904193253/https://www.researchgate.net/publication/5262443_The_phylogeny_of_Cetartiodactyla_The_importance_of_dense_taxon_sampling_missing_data_and_the_remarkable_promise_of_cytochrome_b_to_provide_reliable_species-level_phylogenies |url-status=live }}</ref> [[RBP3|IRBP]] (and [[Von Willebrand factor|vWF]]) gene sequences,<ref>{{Cite journal |last1=Gatesy |first1=John |last2=Milinkovitch |first2=Michel |last3=Waddell |first3=Victor |last4=Stanhope |first4=Michael |year=1999 |title=Stability of Cladistic Relationships between Cetacea and Higher-Level Artiodactyl Taxa |journal=Systematic Biology |volume=48 |issue=1 |pages=6–20 |doi=10.1080/106351599260409 |pmid=12078645 |doi-access=free}}</ref> [[adrenergic receptor]]s,<ref>{{Cite journal |last1=Madsen |first1=Ole |last2=Willemsen |first2=Diederik |last3=Ursing |first3=Björn M. |last4=Arnason |first4=Ulfur |last5=de Jong |first5=Wilfried W. |year=2002 |title=Molecular Evolution of the Mammalian Alpha 2B Adrenergic Receptor |journal=Molecular Biology and Evolution |volume=19 |issue=12 |pages=2150–2160 |doi=10.1093/oxfordjournals.molbev.a004040 |pmid=12446807 |doi-access=free}}</ref> and [[apolipoprotein]]s.<ref name=Amrine2003>{{Cite journal |last1=Amrine-Madsen |first1=Heather |last2=Koepfli |first2=Klaus-Peter |last3=Wayne |first3=Robert K. |last4=Springer |first4=Mark S. |year=2003 |title=A new phylogenetic marker, apolipoprotein B, provides compelling evidence for eutherian relationships |url=https://www.researchgate.net/publication/10647632 |journal=Molecular Phylogenetics and Evolution |volume=28 |issue=2 |pages=225–240 |doi=10.1016/s1055-7903(03)00118-0 |pmid=12878460 |bibcode=2003MolPE..28..225A |access-date=3 September 2018 |archive-date=4 September 2020 |archive-url=https://web.archive.org/web/20200904193254/https://www.researchgate.net/publication/10647632_A_new_phylogenetic_marker_apolipoprotein_B_provides_compelling_evidence_for_eutherian_relationships |url-status=live }}</ref>

In 2001, the fossil limbs of a ''[[Pakicetus]]'' (amphibioid cetacean the size of a wolf) and ''[[Ichthyolestes]]'' (an early whale the size of a fox) were found in Pakistan. They were both [[archaeocete]]s ("ancient whales") from about 48 million years ago (in the Eocene). These findings showed that archaeocetes were more terrestrial than previously thought, and that the special construction of the [[Talus bone|talus]] (ankle bone) with a double-rolled joint surface,{{Clarify|reason=What is a 'double-rolled joint surface'?|date=September 2016}} previously thought to be unique to even-toed ungulates, were also in early cetaceans.<ref name="MamEv">{{Cite book |last1=Savage |first1=R. J. G. |url=https://archive.org/details/mammalevolutioni0000sava |title=Mammal Evolution: an illustrated guide |last2=Long |first2=M. R. |publisher=Facts on File |year=1986 |isbn=978-0-8160-1194-0 |location=New York |pages=[https://archive.org/details/mammalevolutioni0000sava/page/208 208] |url-access=registration}}</ref> The [[mesonychia]]ns, another type of ungulate, did not show this special construction of the talus, and thus was concluded to not have the same ancestors as cetaceans.{{citation needed|date=December 2024}}

[[File:Hippopotamus amphibius.JPG|thumb|Hippos are a geologically young group, which raises questions about their origin.|alt=A hippo splashes in the water]]

The oldest cetaceans date back to the early Eocene (53 million years ago), whereas the oldest known hippopotamus dates back only to the Miocene (15 million years ago). The hippopotamids are descended from the anthracotheres, a family of semiaquatic and terrestrial artiodactyls that appeared in the late Eocene, and are thought to have resembled small- or narrow-headed hippos. Research is therefore focused on anthracotheres (family Anthracotheriidae); one dating from the Eocene to Miocene was declared to be "hippo-like" upon discovery in the 19th century. A study from 2005 showed that the anthracotheres and hippopotamuses had very similar [[skull]]s, but differed in the adaptations of their teeth. It was nevertheless believed that cetaceans and anthracothereres descended from a common ancestor, and that hippopotamuses developed from anthracotheres. A study published in 2015 confirmed this, but also revealed that hippopotamuses were derived from older anthracotherians.<ref name="ReferenceA" /><ref name="ReferenceB">{{Cite journal |last1=Price |first1=Samantha A. |last2=Bininda-Emonds |first2=Olaf R. P. |last3=Gittleman |first3=John L. |year=2005 |title=A complete phylogeny of the whales, dolphins and even-toed hoofed mammals (Cetartiodactyla) |url=https://www.researchgate.net/publication/7665216 |journal=Biological Reviews |volume=80 |issue=3 |pages=445–73 |doi=10.1017/s1464793105006743 |pmid=16094808 |s2cid=45056197 |access-date=3 September 2018 |archive-date=4 September 2020 |archive-url=https://web.archive.org/web/20200904193253/https://www.researchgate.net/publication/7665216_A_complete_phylogeny_of_the_whales_dolphins_and_even-toed_hoofed_mammals_Cetartiodactyla |url-status=live }}</ref> The newly introduced genus ''[[Epirigenys]]'' from Eastern Africa is thus the sister group of hippos.

====Historical classification of Artiodactyla====
[[Linnaeus]] postulated a close relationship between camels and ruminants as early as the mid-1700s.<ref>{{cite book|url=https://books.google.com/books?id=DhchVG_rbQ8C&pg=PA216|publisher=Johns Hopkins University Press|isbn=9780801880223|date=2005|title=The Rise of Placental Mammals: Origins and Relationships of the Major Extant Clades|first1=Kenneth|last1=D. Rose|editor=J. David Archibald|page=216|access-date=20 June 2024|archive-date=21 June 2024|archive-url=https://web.archive.org/web/20240621034329/https://books.google.com/books?id=DhchVG_rbQ8C&pg=PA216#v=onepage&q&f=false|url-status=live}}</ref> [[Henri de Blainville]] recognized the similar anatomy of the limbs of pigs and hippos,{{when|date=July 2016}} and British zoologist [[Richard Owen]] coined the term "even-toed ungulates" and the scientific name "Artiodactyla" in 1848.<ref>{{Cite journal |last=Owen |first=Richard |author-link=Richard Owen |date=1848 |title=Description of Teeth and portions of Jaws of two extinct Anthracotherioid Quadrupeds (Hyopotamus vectianus and Hyop. bovinus) discovered by the Marchioness of Hastings in the Eocene Deposits on the N.W. coast of the Isle of Wight: with an attempt to develope Cuvier's idea of the Classification of Pachyderms by the Number of their Toes |url=https://www.biodiversitylibrary.org/page/37048577 |journal=Quarterly Journal of the Geological Society of London |volume=4 |issue=1 |pages=103–141 |doi=10.1144/GSL.JGS.1848.004.01-02.21 |access-date=February 16, 2024 |archive-date=6 November 2023 |archive-url=https://web.archive.org/web/20231106171352/https://www.biodiversitylibrary.org/page/37048577 |url-status=live }}</ref>

Internal morphology (mainly the stomach and the molars) were used for classification. [[Suines]] (including pigs) and hippopotamuses have molars with well-developed roots and a simple stomach that digests food. Thus, they were grouped together as non-ruminants (porcine). All other even-toed ungulates have molars with a [[selenodont]] construction (crescent-shaped cusps) and have the ability to [[ruminant|ruminate]], which requires regurgitating food and re-chewing it. Differences in stomach construction indicated that rumination evolved independently between [[tylopod]]s and [[ruminant]]s; therefore, tylopods were excluded from [[Ruminantia]].<ref name="ReferenceB"/>

The taxonomy that was widely accepted by the end of the 20th century was:<ref name="ReferenceB"/>

{{Clade|style=font-size:100%;line-height:100%
  |label1={{nowrap|Even-toed ungulates }}
  |1={{Clade
    |label1=[[Suina]]
    |1={{Clade
      |1=[[Suidae]] [[File:Recherches pour servir à l'histoire naturelle des mammifères (Pl. 80) (white background).jpg|50 px]]
      |2=[[Hippopotamidae]]  [[File:Voyage en Abyssinie Plate 2 (white background).jpg|50 px]]
  }}
    |label2=[[Selenodont]]
    |2={{Clade
      |1=[[Tylopoda]] [[File:Cladogram of Cetacea within Artiodactyla (Camelus bactrianus).png|50 px]]
      |label2=[[Ruminant]]s
      |2={{Clade
        |1=[[Tragulidae]] [[File:Tragulus napu - 1818-1842 - Print - Iconographia Zoologica - Special Collections University of Amsterdam - (white background).jpg|50 px]]
        |2=[[Pecora]] [[File:Walia ibex illustration white background.png|50 px]]
    }}
  }}
}}
}}

====Historical classification of Cetacea====
[[File:Mesonyx.jpg|thumb|The [[mesonychia]]ns were long considered ancestors of [[whale]]s.|alt=An illustration of a mesonychian, which looks like a wolf-like animal]]

Modern cetaceans are highly adapted sea creatures which, morphologically, have little in common with land mammals; they are similar to other [[marine mammal]]s, such as [[pinniped|seals]] and [[sea cow]]s, due to [[convergent evolution]]. However, they evolved from originally terrestrial mammals. The most likely ancestors were long thought to be mesonychians—large, carnivorous animals from the early Cenozoic ([[Paleocene]] and [[Eocene]]), which had [[hooves]] instead of [[claw]]s on their feet. Their molars were adapted to a carnivorous diet, resembling the teeth in modern [[toothed whale]]s, and, unlike other mammals, had a uniform construction.<ref>{{Cite journal |last1=Ando |first1=Konami |last2=Fujiwara |first2=Shin-ichi |date=2016-07-10 |title=Farewell to life on land – thoracic strength as a new indicator to determine paleoecology in secondary aquatic mammals |journal=Journal of Anatomy |volume=229 |issue=6 |pages=768–777 |doi=10.1111/joa.12518 |issn=0021-8782 |pmc=5108153 |pmid=27396988}}</ref>

The suspected relations can be shown as follows:<ref name="ReferenceB" /><ref>{{Cite book |first1=Malcolm C. |last1=McKenna |title='Classification of Mammals - Above the Species Level |first2=Susan K. |last2=Bell |publisher=Columbia University Press |year=1997 |isbn=978-0-231-11013-6}}{{Page needed|date=September 2016}}</ref>

{{Clade|style=font-size:100%;line-height:100%
       |label1=[[Paraxonia]]
       |1={{Clade
           |1=[[Artiodactyla]] [[File:Walia ibex illustration white background.png|50 px]]
           |label2=Cetaceamorpha
           |2={{Clade
               |1=[[Mesonychia]] {{Abbr|†|Extinct}}[[File:Synoplotherium112DB.jpg|50 px]]
               |2=[[Cetacea]] [[File:Bowhead-Whale1 (16273933365).jpg|50 px]]
             }}
          }}
       }}

===Inner systematics===
Molecular findings and morphological indications suggest that artiodactyls, as traditionally defined, are paraphyletic with respect to cetaceans. Cetaceans are deeply nested within the former; the two groups together form a [[monophyletic]] taxon, for which the name Cetartiodactyla is sometimes used. Modern nomenclature divides Artiodactyla (or Cetartiodactyla) in four subordinate taxa: camelids (Tylopoda), pigs and peccaries (Suina), ruminants (Ruminantia), and hippos plus cetaceans (Whippomorpha).

The presumed lineages within Artiodactyla can be represented in the following [[cladogram]]:<ref>{{Cite journal |last=Beck |first=N.R. |year=2006 |title=A higher-level MRP supertree of placental mammals |journal=BMC Evol Biol |volume=6 |pages=93 |doi=10.1186/1471-2148-6-93 |pmc=1654192 |pmid=17101039 |doi-access=free }}</ref><ref name="O'Leary2013">{{Cite journal |last1=O'Leary |first1=M.A. |last2=Bloch |first2=J.I. |last3=Flynn |first3=J.J. |last4=Gaudin |first4=T.J. |last5=Giallombardo |first5=A. |last6=Giannini |first6=N.P. |last7=Goldberg |first7=S.L. |last8=Kraatz |first8=B.P. |last9=Luo |first9=Z.-X. |last10=Meng |first10=J. |last11=Ni |first11=X. |last12=Novacek |first12=M.J. |last13=Perini |first13=F.A. |last14=Randall |first14=Z.S. |last15=Rougier |first15=G.W. |year=2013 |title=The Placental Mammal Ancestor and the Post-K-Pg Radiation of Placentals |journal=Science |volume=339 |issue=6120 |pages=662–667 |bibcode=2013Sci...339..662O |doi=10.1126/science.1229237 |pmid=23393258 |hdl-access=free |last16=Sargis |first16=E.J. |last17=Silcox |first17=M.T. |last18=Simmons |first18=N.B. |last19=Spaulding |first19=M. |last20=Velazco |first20=P.M. |last21=Weksler |first21=M. |last22=Wible |first22=J.R. |last23=Cirranello |first23=A.L. |s2cid=206544776 |hdl=11336/7302}}</ref><ref name="Song2012">{{Cite journal |last1=Song |first1=S. |last2=Liu |first2=L. |last3=Edwards |first3=S.V. |last4=Wu |first4=S. |year=2012 |title=Resolving conflict in eutherian mammal phylogeny using phylogenomics and the multispecies coalescent model |journal=Proceedings of the National Academy of Sciences |volume=109 |issue=37 |pages=14942–14947 |bibcode=2012PNAS..10914942S |doi=10.1073/pnas.1211733109 |pmc=3443116 |pmid=22930817 |doi-access=free}}</ref><ref name="dos Reis2012">{{Cite journal |last1=dos Reis |first1=M. |last2=Inoue |first2=J. |last3=Hasegawa |first3=M. |last4=Asher |first4=R.J. |last5=Donoghue |first5=P.C.J. |last6=Yang |first6=Z. |year=2012 |title=Phylogenomic datasets provide both precision and accuracy in estimating the timescale of placental mammal phylogeny |journal=Proceedings of the Royal Society B: Biological Sciences |volume=279 |issue=1742 |pages=3491–3500 |doi=10.1098/rspb.2012.0683 |pmc=3396900 |pmid=22628470 |doi-access=free}}</ref><ref name="Upham2019">{{Cite journal |last1=Upham |first1=N.S. |last2=Esselstyn |first2=J.A. |last3=Jetz |first3=W. |year=2019 |title=Inferring the mammal tree: Species-level sets of phylogenies for questions in ecology, evolution, and conservation |journal=PLOS Biology |volume=17 |issue=12 |pages=e3000494 |doi=10.1371/journal.pbio.3000494 |pmc=6892540 |pmid=31800571 |doi-access=free}}(see e.g. Fig S10)</ref>

{{clade
    |style=font-size:100%;line-height:100%
    |label1='''Artiodactyla'''
    |1={{clade
        |1=[[Tylopoda]] (camels) [[File:Cladogram of Cetacea within Artiodactyla (Camelus bactrianus).png|50 px]]
        |label2=[[Artiofabula]]
        |2={{clade
            |1=[[Suina]] (pigs) [[File:Recherches pour servir à l'histoire naturelle des mammifères (Pl. 80) (white background).jpg|50 px]]
            |label2=[[Cetruminantia]]
            |2={{clade
                |label1=[[Ruminantia]] (ruminants)
                |1={{clade
                    |1=[[Tragulidae]] (mouse deer) [[File:Tragulus napu - 1818-1842 - Print - Iconographia Zoologica - Special Collections University of Amsterdam - (white background).jpg|50 px]]
                    |2=[[Pecora]] (horn bearers) [[File:Walia ibex illustration white background.png|50 px]]
              }}
                |label2=[[Cetancodonta]]
                |sublabel2=(or [[Whippomorpha]])
                |2={{clade
                    |1=[[Hippopotamidae]] (hippopotamuses) [[File:Voyage en Abyssinie Plate 2 (white background).jpg|50 px]]
                    |2=[[Cetacea]] (whales) [[File:Bowhead-Whale1 (16273933365).jpg|50 px]]
              }}
          }}
       }}
    }}
 }}
[[File:Camelus dromedarius in Singapore Zoo.JPG|thumb|[[Camel]]s are now considered a sister group of [[Artiofabula]].|alt=A camel chillaxing.]]
[[File:Antilocapra americana.jpg|thumb|The [[pronghorn]] is the only extant antilocaprid.|alt=A pronghorn]]

The four summarized Artiodactyla taxa are divided into ten extant families:<ref>{{Cite book |title=Mammal Species of the World |publisher=Johns Hopkins University Press |year=2005 |isbn=978-0-8018-8221-0 |editor-last=Wilson, D. E. |edition=3rd |pages=111–184 |editor-last2=Reeder, D. M.}}</ref>
* The camelids ([[Tylopoda]]) comprise only one family, [[Camelidae]]. It is a species-poor artiodactyl suborder of North American origin<ref name="Cui2007">{{Cite journal |last1=Cui |first1=P. |last2=Ji |first2=R. |last3=Ding |first3=F. |last4=Qi |first4=D. |last5=Gao |first5=H. |last6=Meng |first6=H. |last7=Yu |first7=J. |last8=Hu |first8=S. |last9=Zhang |first9=H. |year=2007 |title=A complete mitochondrial genome sequence of the wild two-humped camel (''Camelus bactrianus ferus''): an evolutionary history of Camelidae |journal=BMC Genomics |volume=8 |issue=1 |pages=241 |doi=10.1186/1471-2164-8-241 |pmc=1939714 |pmid=17640355 |doi-access=free }}</ref> that is well adapted to extreme habitats—the [[dromedary]] and [[Bactrian camel|Bactrian]] camels in the Old World deserts and the [[guanaco]]s, llamas, [[vicuña]]s, and [[alpaca]]s in South American high mountain regions.
* The pig-like creatures ([[Suina]]) are made up of two families:
** The pigs ([[Suidae]]) are limited to the Old World. These include the [[wild boar]] and the domesticated form, the [[domestic pig]].
** The peccaries ([[Tayassuidae]]) are named after glands on their belly and are indigenous to Central and South America.
* The ruminants ([[Ruminantia]]) consist of six families:
** The mouse deer ([[Tragulidae]]) are the smallest and most primitive even-toed-ruminants; they inhabit forests of Africa and Asia.
** The giraffe-like creatures ([[Giraffidae]]) are composed of two species: the giraffe and the [[okapi]].
** The musk deer ([[Moschidae]]) is indigenous to East Asia.
** The antilocaprids ([[Antilocapridae]]) of North America comprise only one extant species: the [[pronghorn]].
** The deer ([[Cervidae]]) are made up of about 45 species, which are characterized by a pair of [[antler]]s (generally only in males). They are spread across Europe, Asia, and the Americas. This group includes, among other species, the [[red deer]], [[moose]], [[elk]] (wapiti), and [[reindeer]] (caribou).
** The bovids ([[Bovidae]]) are the most species-rich. Among them are [[Bos|cattle]], [[Ovis|sheep]], [[Caprinae|caprine]]s, and [[antelope]]s, and more.
* The [[Whippomorpha|whippomorphs]] include hippos and cetaceans:
** The hippos ([[Hippopotamidae]]) comprise two groups, the [[common hippo]] and the [[pygmy hippo]].
** The [[cetacea]]ns comprise 72 species and two parvorders: toothed whales ([[Odontoceti]]) and baleen whales ([[Mysticeti]])

Although deer, musk deer, and pronghorns have traditionally been summarized as cervids (Cervioidea), molecular studies provide different—and inconsistent—results, so the question of phylogenetic systematics of infraorder [[Pecora]] (the horned ruminants) for the time being, cannot be answered.

[[File:Indohyus BW.jpg|thumb|Reconstruction of ''[[Indohyus]]''|alt=Illustration of an Indohyus, a mouse-like mammal]]