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South American native ungulates

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South American native ungulates,commonly abbreviated asSANUs,areextinctungulate-likemammalsthat were indigenous toSouth Americafrom thePaleocene(from at least 63 million years ago) until the end of theLate Pleistocene(~12,000 years ago). They represented a dominant element of South America'sCenozoicterrestrial mammal fauna prior to the arrival of living unguate groups in South America during thePlioceneandPleistoceneas part of theGreat American Interchange.They comprise five major groups conventionally ranked asorders—Astrapotheria,Litopterna,Notoungulata,Pyrotheria,andXenungulata—as well as the primitive "condylarth"groupsDidolodontidaeandKollpaniinae.It has been proposed that some or all of the members of this group form a clade, namedMeridiungulata,though the relationships of South American ungulates remain largely unresolved. The two largest groups of South American ungulates, the notoungulates and the litopterns, were the only groups to persist beyond the midMiocene.Only a few (mostly large) species of notoungulates and litopterns survived until theend-Pleistocene extinction eventaround 12,000 years ago where they became extinct with most other large mammals in the Americas, shortly after the first arrival of humans into the region.

Meridiungulata
Temporal range:Paleocene–Holocene
Toxodon,anotoungulate
Thesodon,alitoptern
Scientific classificationEdit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Infraclass: Placentalia
Clade: †Meridiungulata
McKenna 1975
Orders

Though most SANUs lived in South America, astrapotheres and litopterns are known fromEoceneaged deposits in theAntarctic Peninsula[1]and the notoungulateMixotoxodonspread as far north as what is now Texas during the Pleistocene as part of the Great American Biotic Interchange.[2]

The relationships of SANUs to living mammals has been historically uncertain, though analysis of DNA and collagen suggests that at least notoungulates and litopterns are members ofLaurasiatheria,and closely related to livingperissodactyls.

Taxonomy

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Meridiungulata might have originated inSouth Americafrom aNorth Americancondylarthancestor,[3]and they may be members of the cladeLaurasiatheria,related to other ungulates, includingartiodactylsandperissodactyls.[4]It has, however, been suggested the Meridiungulata are part of a different macro-group of placental mammals calledAtlantogenata.[5][1]

Much of the evolution of meridiungulates occurred in isolation from other ungulates, a great example ofconvergent evolution.However, the argument that meridiungulates are related to artiodactyls and perissodactyls needs support from molecular sequencing. Somepaleontologistshave also challenged themonophylyof Meridiungulata by suggesting that the pyrotheres are more closely related to other mammals, such asEmbrithopoda(an African order possibly related toelephants), than to other South American ungulates.[6]

Molecular sequence data from both collagen[7][8]and mitochondrial DNA[9]supports that litopterns and notoungulates are most closely related toPerissodactyla(the group containingequids,rhinoceroses,andtapirs) among living mammals, as part of the cladePanperissodactyla,making them true ungulates, which has also been supported by some analyses of morphology.[10][11]However, other morphological analyses have placed Litopterna elsewhere within Laurasiatheria.[12][13]Didolodontids may be closely related to litopterns,[12][14]and it has been proposed that they should be classified within Litopterna,[15]but some analyses do not find them to be close relatives.[10][11]

Molecular sequence data from collagen suggests Notoungulata and Litopterna are more closely related to each other than to Perissodactyla, suggesting that at least part of Meridiungulata is monophyletic.[7][8]By contrast, morphology-based analyses have found a range of possible positions for notoungulates. They have been found to be elsewhere within Laurasiatheria,[13]withinAfrotheria,[12][14][16]and as stem-groupatlantogenatans.[13]A position within Afrotheria has been argued to be unlikely on biogeographic grounds, and some of the afrotherian characteristics present in notoungulates have been refuted.[1]

Litopterns and notoungulates are the only South American ungulates to have gone extinct recently enough for molecular data to be available, so the relationships of astrapotheres, pyrotheres, and xenungulates must be determined based on morphology alone.[8][1]

The clade Sudamericungulata has been proposed to encompass astrapotheres, notoungulates, pyrotheres, and xenoungulates but not litopterns.[14]Such a clade had been found in previous studies, but left unnamed.[16][11]The study proposing the name Sudamericungulata found them to be afrotheres.[14]The study proposing Sudamericungulata was questioned in a later study, who suggested that the taxon and character sampling in the analysis was poor (including only a single perissodactyl), and that the placement of Sudamericungulata within Afrotheria was not robustly supported, and that a placement withinLaurasiatheriawas supported for Sudamericungulata and Litopterna when Afrotheria and Laurasiatheria were constrained to be monophyletic by molecular results.[17]

A 2024 study based on morphology supported the monophyly of Meridiungulata as traditionally defined.[18]

Evolution

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The earliest SANUs appeared during the earlyPaleocene,around 63-65 million years ago. SANU diversity reached its greatest extent during the lateEoceneandOligoceneperiods. During theMiocene,genus and species diversity was stable, but family diversity declined. During thePlioceneandPleistoceneepochs, SANU diversity substantially declined to the point that there were only a handful of living species by theLate Pleistocene.[1]The causes of the decline are unclear, but may be due to climatic change,[19]or competition/predation from new arrivals from North America as part of theGreat American interchange.[1]

Notes

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  1. ^abcdefCroft, Gelfo & López 2020.
  2. ^Lundelius et al. 2013.
  3. ^Muizon & Cifelli 2000
  4. ^Hunter & Janis 2006
  5. ^Naish 2008
  6. ^Shockey & Anaya 2004
  7. ^abBuckley 2015.
  8. ^abcWelker et al. 2015.
  9. ^Westbury et al. 2017.
  10. ^abChimento & Agnolin 2020.
  11. ^abcMacPhee et al. 2021.
  12. ^abcO'Leary et al. 2013.
  13. ^abcHalliday, Upchurch & Goswami 2017.
  14. ^abcdAvilla & Mothé 2021.
  15. ^Gelfo, López & Lorente 2016.
  16. ^abde Muizon et al. 2015.
  17. ^Kramarz, Alejandro G.; Macphee, Ross D. E. (March 2023)."Did some extinct South American native ungulates arise from an afrothere ancestor? A critical appraisal of Avilla and Mothé's (2021) Sudamericungulata – Panameridiungulata hypothesis".Journal of Mammalian Evolution.30(1): 67–77.doi:10.1007/s10914-022-09633-5.ISSN1064-7554.S2CID253433775.
  18. ^Püschel, Hans P; Shelley, Sarah L; Williamson, Thomas E; Perini, Fernando A; Wible, John R; Brusatte, Stephen L (2024-09-02)."A new dentition-based phylogeny of Litopterna (Mammalia: Placentalia) and 'archaic' South American ungulates".Zoological Journal of the Linnean Society.202(1).doi:10.1093/zoolinnean/zlae095.ISSN0024-4082.
  19. ^Freitas-Oliveira, Roniel; Lima-Ribeiro, Matheus; Faleiro, Frederico Valtuille; Jardim, Lucas; Terribile, Levi Carina (June 2024)."Temperature changes affected mammal dispersal during the Great American Biotic Interchange".Journal of Mammalian Evolution.31(2).doi:10.1007/s10914-024-09717-4.ISSN1064-7554.

References

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