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Meridiungulata Temporal range: Paleocene–Holocene PreꞒ Ꞓ O S D C P T J K Pg N
Toxodon, a notoungulate
Thesodon, a litoptern
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Infraclass:	Placentalia
Clade:	†Meridiungulata McKenna 1975
Orders
†Astrapotheria †Litopterna †Notoungulata †Pyrotheria †Xenungulata

South American native ungulates, commonly abbreviated as SANUs, are extinct ungulate-like mammals that were indigenous to South America from the Paleocene (from at least 63 million years ago) until the end of the Late Pleistocene (~12,000 years ago). They represented a dominant element of South America's Cenozoic terrestrial mammal fauna prior to the arrival of living unguate groups in South America during the Pliocene and Pleistocene as part of the Great American Interchange. They comprise five major groups conventionally ranked as orders—Astrapotheria, Litopterna, Notoungulata, Pyrotheria, and Xenungulata—as well as the primitive "condylarth" groups Didolodontidae and Kollpaniinae. It has been proposed that some or all of the members of this group form a clade, named Meridiungulata, 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 mid Miocene. Only a few (mostly large) species of notoungulates and litopterns survived until the end-Pleistocene extinction event around 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.

Though most SANUs lived in South America, astrapotheres and litopterns are known from Eocene aged deposits in the Antarctic Peninsula and the notoungulate Mixotoxodon spread as far north as what is now Texas during the Pleistocene as part of the Great American Biotic Interchange.

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 of Laurasiatheria, and closely related to living perissodactyls.

Taxonomy

Meridiungulata might have originated in South America from a North American condylarth ancestor, and they may be members of the clade Laurasiatheria, related to other ungulates, including artiodactyls and perissodactyls. It has, however, been suggested the Meridiungulata are part of a different macro-group of placental mammals called Atlantogenata.

Much of the evolution of meridiungulates occurred in isolation from other ungulates, a great example of convergent evolution. However, the argument that meridiungulates are related to artiodactyls and perissodactyls needs support from molecular sequencing. Some paleontologists have also challenged the monophyly of Meridiungulata by suggesting that the pyrotheres are more closely related to other mammals, such as Embrithopoda (an African order possibly related to elephants), than to other South American ungulates.

Molecular sequence data from both collagen and mitochondrial DNA supports that litopterns and notoungulates are most closely related to Perissodactyla (the group containing equids, rhinoceroses, and tapirs) among living mammals, as part of the clade Panperissodactyla, making them true ungulates, which has also been supported by some analyses of morphology. However, other morphological analyses have placed Litopterna elsewhere within Laurasiatheria. Didolodontids may be closely related to litopterns, and it has been proposed that they should be classified within Litopterna, but some analyses do not find them to be close relatives.

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. By contrast, morphology-based analyses have found a range of possible positions for notoungulates. They have been found to be elsewhere within Laurasiatheria, within Afrotheria, and as stem-group atlantogenatans. 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.

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.

The clade Sudamericungulata has been proposed to encompass astrapotheres, notoungulates, pyrotheres, and xenoungulates but not litopterns. Such a clade had been found in previous studies, but left unnamed. The study proposing the name Sudamericungulata found them to be afrotheres. 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 within Laurasiatheria was supported for Sudamericungulata and Litopterna when Afrotheria and Laurasiatheria were constrained to be monophyletic by molecular results.

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

Evolution

The earliest SANUs appeared during the early Paleocene, around 63-65 million years ago. SANU diversity reached its greatest extent during the late Eocene and Oligocene periods. During the Miocene, genus and species diversity was stable, but family diversity declined. During the Pliocene and Pleistocene epochs, SANU diversity substantially declined to the point that there were only a handful of living species by the Late Pleistocene. The causes of the decline are unclear, but may be due to climatic change, or competition/predation from new arrivals from North America as part of the Great American interchange.

Notes

1. ^ Croft, Gelfo & López 2020.
2. Lundelius et al. 2013.
3. Muizon & Cifelli 2000
4. Hunter & Janis 2006
5. Naish 2008
6. Shockey & Anaya 2004
7. ^ Buckley 2015.
8. ^ Welker et al. 2015.
9. Westbury et al. 2017.
10. ^ Chimento & Agnolin 2020.
11. ^ MacPhee et al. 2021.
12. ^ O'Leary et al. 2013.
13. ^ Halliday, Upchurch & Goswami 2017.
14. ^ Avilla & Mothé 2021.
15. Gelfo, López & Lorente 2016.
16. ^ de 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. ISSN 1064-7554. S2CID 253433775.
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. ISSN 0024-4082.
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. ISSN 1064-7554.

References

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v t e Genera of South American native ungulates
Kingdom: Animalia Phylum: Chordata Class: Mammalia Superorder: Laurasiatheria
Xenungulata, Pyrotheria, Astrapotheria, and other minor groups †Kollpaniidae? Andinodus Molinodus Pascualodus? Pucanodus Simoclaenus Tiuclaenus †Didolodontidae Didolodus Enneoconus Ernestokokenia Escribania? Lamegoia Paulogervaisia Raulvaccia Ricardocifellia Saltaodus Umayodus Xesmodon †Protolipternidae Asmithwoodwardia Miguelsoria Protolipterna †Xenungulata †Carodniidae Carodnia Etayoa Notoetayoa Rodcania †Pyrotheria †Colombitheriidae Colombitherium Proticia †Pyrotheriidae Baguatherium Berracotherium Carolozittelia Griphodon Propyrotherium Pyrotherium †Astrapotheria Eoastrapostylops †Trigonostylopidae Shecenia Tetragonostylops Trigonostylops †Astrapotheriidae Antarctodon Astrapodon Comahuetherium Liarthrus Maddenia Parastrapotherium †Albertogaudryinae Albertogaudrya Astraponotus †Astrapotheriinae Astrapothericulus Astrapotherium Scaglia †Uruguaytheriinae Granastrapotherium Hilarcotherium Uruguaytherium Xenastrapotherium
Litopterna †Eulitopterna †Adianthidae Adianthus Proadiantus Proectocion? Proheptaconus Thadanius Tricoelodus †Macraucheniidae Polymorphis †Cramaucheniinae Caliphrium Coniopternium Cramauchenia Llullataruca Phoenixauchenia Pternoconius Theosodon †Macraucheniinae Cullinia Huayqueriana Macrauchenia Macraucheniopsis Micrauchenia Oxyodontherium Paranauchenia Promacrauchenia Scalabrinitherium Windhausenia Xenorhinotherium †Proterotherioidea †Anisolambdidae †Anisolambdinae Anisolambda Eolicaphrium Guilielmofloweria Lambdaconops Paranisolambda Polyacrodon Protheosodon Wainka †Sparnotheriodontinae Heteroglyphis Notiolofos Phoradiadius Sparnotheriodon Victorlemoinea †Proterotheriidae Mesolicaphrium Neodolodus Olisanophus Promylophis Prothoatherium Pseudobrachytherium Salladolodus †Megadolodinae Bounodus Megadolodus †Proterotheriinae Anisolophus Brachytherium Diadiaphorus Diplasiotherium Eoauchenia Epecuenia Epitherium Lambdaconus Neobrachytherium Neolicaphrium Paramacrauchenia Picturotherium Prolicaphrium Proterotherium Tetramerorhinus Thoatheriopsis Thoatherium Uruguayodon Villarroelia †Notopterna †Amilnedwardsiidae Amilnedwardsia Ernestohaeckelia Rutimeyeria †Indaleciidae Adiantoides Indalecia †Notonychopidae Notonychops Requisia Incertae sedis Kyraodus Proacrodon
Notoungulata incertae sedis Acoelodus Archaeogaia Carolodarwinia Perutherium †Notioprogonia Satshatemnus Seudenius †Henricosborniidae Henricosbornia Nanolophodon Othnielmarshia Peripantostylops Simpsonotus †Notostylopidae Boreastylops Chilestylops Edvardotrouessartia Homalostylops Notostylops Otrhonia Parastylops †Toxodontia †Homalodotheriidae Asmodeus Chasicotherium Homalodotherium Trigonolophodon †Isotemnidae Anisotemnus Coelostylodon Distylophorus Hedralophus Isotemnus Lophocoelus Pampatemnus Periphragnis Pleurocoelodon Pleurostylodon Rhyphodon Thomashuxleya †Eutoxodontia †Leontiniidae Anayatherium Ancylocoelus Colpodon Coquenia Elmerriggsia Gualta Henricofilholia Huilatherium Leontinia Martinmiguelia Purperia? Scarrittia Taubatherium Termastherium †Notohippidae Acoelohyrax Argyrohippus Deuterotherium? Edvardocopeia Eomorphippus Eurygenium Mendozahippus Moqueguahippus Morphippus Nesohippus Notohippus Pampahippus Pascualihippus Patagonhippus Perhippidion Plexotemnus Puelia Purperia? Rhynchippus Rosendo Stilhippus Teushentherium Trimerostephanos †Toxodontidae †Nesodontinae Adinotherium Nesodon Proadinotherium †Toxodontinae Abothrodon Andinotoxodon Calchaquitherium Ceratoxodon Charruatoxodon Dinotoxodon Eutomodus Falcontoxodon Gyrinodon Haplodontherium Hemixotodon Hoffstetterius Hyperoxotodon Mesenodon Mesotoxodon Minitoxodon Mixotoxodon Neoadinotherium Neotoxodon Nesodonopsis Nonotherium Ocnerotherium Palyeidodon Paratrigodon Pericotoxodon Piauhytherium Pisanodon Plesiotoxodon Posnanskytherium Prototrigodon Stenotephanos Stereotoxodon Toxodon Toxodontherium Trigodon Trigodonops Xotodon †Typotheria Campanorco Griphotherion †Archaeopithecidae Archaeopithecus Teratopithecus †Oldfieldthomasiidae Allalmeia Brachystephanus Camargomendesia Colbertia Dolichostylodon Itaboraitherium Kibenikhoria Maxschlosseria Oldfieldthomasia Paginula Suniodon Tsamnichoria Ultrapithecus Xenostephanus †Interatheriidae Antofagastia Ignigena Johnbell Munizia Punapithecus †Interatheriinae Archaeophylus Argyrohyrax Boleatherium Brucemacfaddenia Caenophilus Choichephilum Cochilius Eopachyrucos Federicoanaya Interatherium Juchuysillu Miocochilius Neoicochilus Patriarchus Proargyrohyrax Progaleopithecus Protypotherium Santiagorothia †Notopithecinae Antepithecus Guilielmoscottia Notopithecus Transpithecus †Mesotheriidae Fiandraia? Trachytherus †Mesotheriinae Altitypotherium Caraguatypotherium Eotypotherium Eutypotherium Hypsitherium Mesotherium Microtypotherium Plesiotypotherium Pseudotypotherium Rusconitherium Typotheriopsis †Archaeohyracidae Archaeohyrax Archaeotypotherium Bryanpattersonia Eohyrax Pascualhyrax Protarchaeohyrax Pseudhyrax Punahyrax †Hegetotheriidae †Hegetotheriinae Ethegotherium Hegetotheriopsis Hegetotherium Hemihegetotherium Prohegetotherium Pseudohegetotherium Sallatherium †Pachyrukhinae Medistylus Propachyrucos Prosotherium Tremacyllus †Pachyrukhini Pachyrukhos Paedotherium Tremacyllus

• Meridiungulata
• Cenozoic mammals of South America
• Mammal unranked clades
• Prehistoric mammals of South America
• Ungulates
• Taxa named by Malcolm McKenna