toxodon

File:Toxodon platensis.jpg

Charles Darwin, who was in South America as part of the second voyaging expedition of HMS Beagle, was one of the first to collect Toxodon fossils. In September–October 1832 and October 1833, Darwin collected several isolated teeth as well as a mandible from various localities in northern Argentina. On November 26, 1833, Darwin paid 18 pence (equivalent to £6.40 in 2018) for a T. platensis skull from a farmer in Uruguay.{{cite magazine |last=Quammen |first=D. |date=February 2009 |title=Darwin's first clues |magazine=National Geographic |page=45}}{{Cite web |title=Darwin's Fossil Mammals - Toxodon platensis - cranium - Data Portal |url=https://data.nhm.ac.uk/dataset/darwins-fossil-mammals/resource/dadf577f-fa52-4f48-8cdb-d11c98448009 |access-date=2024-11-28 |website=data.nhm.ac.uk |language=en-GB}} In his book covering the expedition, The Voyage of the Beagle. Darwin wrote, "November 26th – I set out on my return in a direct line for Montevideo. Having heard of some giant's bones at a neighbouring farm-house on the Sarandis, a small stream entering the Rio Negro, I rode there accompanied by my host, and purchased for the value of eighteen pence the head of the Toxodon." The skull had been propped up against a fence and been used as target practice for throwing stones by local children, who had knocked out its teeth.{{cite book |last=Darwin |first=Charles |title=The Voyage of the Beagle |date=1997 |publisher=Penguin |isbn=978-0-14-043268-8 |editor1-last=Browne |editor1-first=J. |quote=Read, 19th April 1837. A detailed account will appear in the first part of the zoology of Voyage of the Beagle. |editor2-last=Neve |editor2-first=M. |orig-year=1839}}{{Cite news |last=Kennedy |first=Maev |date=2018-04-06 |title=Darwin's lost fossils – including a sloth the size of a car – to be made public |url=https://www.theguardian.com/science/2018/apr/06/charles-darwin-lost-fossils-including-a-sloth-the-size-of-a-car-to-be-made-public |access-date=2024-11-28 |work=The Guardian |language=en-GB |issn=0261-3077}} Since Darwin discovered that the fossils of similar mammals of South America were different from those in Europe, he invoked many debates about the evolution and natural selection of animals.

In his own words, Darwin wrote down in his journal,

{{blockquote| Lastly, the Toxodon, perhaps one of the strangest animals ever discovered: In size it equaled an elephant or megatherium, but the structure of its teeth, as Mr. Owen states, proves indisputably that it was intimately related to the Gnawers, the order which, at the present day, includes most of the smallest quadrupeds: In many details it is allied to the Pachydermata: Judging from the position of its eyes, ears, and nostrils, it was probably aquatic, like the Dugong and Manatee, to which it is also allied. How wonderfully are the different Orders, at the present time so well separated, blended together in different points of the structure of the Toxodon!}}

Toxodon and its type species, T. platensis, were described in 1837 by Richard Owen based on remains collected by Darwin, in a paper titled "A description of the cranium of the Toxodon platensis, a gigantic extinct mammiferous species, referrible by its dentition to the Rodentia, but with affinities to the Pachydermata and the herbivorous Cetacea", reflecting the many unusual characteristics of its anatomy.Fernicola, J. C., Vizcaino, S. F., & De Iuliis, G. (2009). The fossil mammals collected by Charles Darwin in South America during his travels on board the HMS Beagle. Revista De La Asociación Geológica Argentina, 64(1), 147-159. Retrieved from https://revista.geologica.org.ar/raga/article/view/1339

Toxodon is a member of Notoungulata, a group of South American native ungulates that had been part of the fauna of South America since the Paleocene, over 60 million years ago, and had evolved in isolation in South America, prior to the arrival of living ungulates in South America around 2.5 million years ago as part of the Great American Interchange. Notoungulata represents the most diverse group of indigenous South American ungulates, with over 150 described genera in 13 different families.{{Cite journal |last1=Rezende Castro |first1=Luis Otavio |last2=García-López |first2=Daniel A. |last3=Bergqvist |first3=Lilian Paglarelli |last4=De Araújo-Júnior |first4=Hermínio Ismael |date=2021-06-30 |title=A New Basal Notoungulate from the Itaboraí Basin (Paleogene) of Brazil |url=https://bioone.org/journals/ameghiniana/volume-58/issue-3/AMGH.05.02.2021.3387/A-New-Basal-Notoungulate-from-the-Itabora%c3%ad-Basin-Paleogene-of/10.5710/AMGH.05.02.2021.3387.full |journal=Ameghiniana |volume=58 |issue=3 |doi=10.5710/AMGH.05.02.2021.3387 |issn=0002-7014 |s2cid=234220780}} Notoungulates are morphologically diverse, including forms morphologically distant from Toxodon such as rodent and rabbit-like forms.

Analysis of collagen sequences obtained from Toxodon as well as from Macrauchenia, a member of another indigenous South American ungulate order, Litopterna, found that notoungulates and litopterns were closely related to each other, and form a sister group to perissodactyls (which contains equids, rhinoceroses and tapirs) as part of the clade Panperissodactyla, making them true ungulates.{{cite journal |display-authors=6 |vauthors=Welker F, Collins MJ, Thomas JA, Wadsley M, Brace S, Cappellini E, Turvey ST, Reguero M, Gelfo JN, Kramarz A, Burger J, Thomas-Oates J, Ashford DA, Ashton PD, Rowsell K, Porter DM, Kessler B, Fischer R, Baessmann C, Kaspar S, Olsen JV, Kiley P, Elliott JA, Kelstrup CD, Mullin V, Hofreiter M, Willerslev E, Hublin JJ, Orlando L, Barnes I, MacPhee RD |date=June 2015 |title=Ancient proteins resolve the evolutionary history of Darwin's South American ungulates |url=http://eprints.whiterose.ac.uk/91438/1/Welker_postprint.docx |journal=Nature |volume=522 |issue=7554 |pages=81–4 |bibcode=2015Natur.522...81W |doi=10.1038/nature14249 |pmid=25799987 |s2cid=4467386 |hdl-access=free |hdl=11336/14769}}{{cite journal |last=Buckley |first=M. |date=7 May 2015 |title=Ancient collagen reveals evolutionary history of the endemic South American 'ungulates' |journal=Proceedings of the Royal Society B: Biological Sciences |volume=282 |issue=1806 |pages=20142671 |doi=10.1098/rspb.2014.2671 |pmc=4426609 |pmid=25833851}} This finding has been corroborated by an analysis of mitochondrial DNA extracted from a Macrauchenia fossil, which yielded a date of 66 million years ago for the time of the split from perissodactyls.{{cite journal |display-authors=6 |vauthors=Westbury M, Baleka S, Barlow A, Hartmann S, Paijmans JL, Kramarz A, Forasiepi AM, Bond M, Gelfo JN, Reguero MA, López-Mendoza P, Taglioretti M, Scaglia F, Rinderknecht A, Jones W, Mena F, Billet G, de Muizon C, Aguilar JL, MacPhee RD, Hofreiter M |date=June 2017 |title=A mitogenomic timetree for Darwin's enigmatic South American mammal Macrauchenia patachonica |journal=Nature Communications |volume=8 |page=15951 |bibcode=2017NatCo...815951W |doi=10.1038/ncomms15951 |pmc=5490259 |pmid=28654082}}

Toxodon belongs to Toxodontidae, a large bodied group of notoungulates which first appeared in the Late Oligocene (Deseadan), ~28-23 million years ago,{{Cite journal |last1=Bonini |first1=Ricardo A. |last2=Schmidt |first2=Gabriela I. |last3=Reguero |first3=Marcelo A. |last4=Cerdeño |first4=Esperanza |last5=Candela |first5=Adriana M. |last6=Solís |first6=Natalia |date=May 2017 |title=First record of Toxodontidae (Mammalia, Notoungulata) from the late Miocene–early Pliocene of the southern central Andes, NW Argentina |url=https://www.cambridge.org/core/product/identifier/S0022336016001608/type/journal_article |journal=Journal of Paleontology |language=en |volume=91 |issue=3 |pages=566–576 |doi=10.1017/jpa.2016.160 |bibcode=2017JPal...91..566B |issn=0022-3360|hdl=11336/49805 |hdl-access=free }} and underwent a great radiation during the Miocene epoch (~23-5.3 million years ago), when they reached their apex of diversity.{{Cite journal |last1=Ferrero |first1=Brenda S. |last2=Schmidt |first2=Gabriela I. |last3=Costamagna |first3=Donato |last4=Miño-Boilini |first4=Ángel R. |last5=Zurita |first5=Alfredo E. |last6=Quiñones |first6=Sofía I. |last7=Cuadrelli |first7=Francisco |last8=Luna |first8=Carlos A. |last9=Solís |first9=Natalia |last10=Candela |first10=Adriana M. |date=March 2024 |title=First record of Posnanskytherium (Notoungulata, Toxodontidae) in the late Neogene of eastern Puna, Argentina |url=https://link.springer.com/10.1007/s10914-023-09700-5 |journal=Journal of Mammalian Evolution |language=en |volume=31 |issue=1 |doi=10.1007/s10914-023-09700-5 |issn=1064-7554}} The diversity of toxodontids, along with other notoungulates began to decline from around the Pliocene onwards, possibly as a result of climate change, as well as the arrival of competitors and predators from North America during the Great American Interchange following formation of the Isthmus of Panama.{{Cite journal |last1=Solórzano |first1=Andrés |last2=Núñez-Flores |first2=Mónica |last3=Rodríguez-Serrano |first3=Enrique |date=November 2024 |title=The rise and fall of notoungulates: How Andean uplift, available land area, competition, and depredation driven its diversification dynamics |url=https://linkinghub.elsevier.com/retrieve/pii/S1342937X24002193 |journal=Gondwana Research |language=en |volume=135 |pages=116–132 |doi=10.1016/j.gr.2024.08.002|bibcode=2024GondR.135..116S }} By the Late Pleistocene (Lujanian), the once great diversity of notoungulates had declined to only a few of species of toxodontids (belong to the genera Toxodon, Mixotoxodon, Trigodonops and Piauhytherium, the last possibly being a synonym of Trigodonops) with all other notoungulate families having become extinct.

Cladogram of Toxodontidae, showing the position of Toxodon relative to other toxodontids, after Forasiepi et al., 2014:{{cite journal |display-authors=6 |vauthors=Forasiepi AM, Cerdeno E, Bond M, Schmidt GI, Naipauer M, Straehl FR, Martinelli AG, Garrido AC, Schmitz MD, Crowley JL |year=2014 |title=New toxodontid (Notoungulata) from the Early Miocene of Mendoza, Argentina |url=http://sedici.unlp.edu.ar/handle/10915/127531 |journal=Paläontologische Zeitschrift |volume=89 |issue=3 |pages=611–634 |doi=10.1007/s12542-014-0233-5 |s2cid=129293436 |hdl-access=free |hdl=11336/20443}}

{{clade| style=font-size:85%; line-height:85%

|label1=†Notoungulata

|1={{clade

|1=†Pampahippus arenalesi

|2={{clade

|1={{clade

|1=†Rhynchippus spp.

|2={{clade

|1=†Scarrittia canquelensis

|2=†Leontinia gaudri }} }}

|label2=†Toxodontidae

|2={{clade

|1=†Proadinotherium leptognathum

|2={{clade

|1={{clade

|1=†Adinotherium spp.

|2={{clade

|1=†Nesodon taweretus

|2=†Nesodon imbricatus }} }}

|2={{clade

|1=†Palyeidodon obtusum

|2={{clade

|1=†Hyperoxotodon speciosus

|2={{clade

|1={{clade

|1=†Nonotherium henningi

|2=†Xotodon spp. }}

|2={{clade

|1={{clade

|1=†Andinotoxodon bolivariensis

|2={{clade

|1={{clade

|1=†Dinotoxodon paranensis

|2=†Toxodon platensis }}

|2={{clade

|1=†Gyrinodon quassus

|2={{clade

|1=†Ocnerotherium intermedium

|2=†Hoffstetterius imperator }} }} }} }}

|2={{clade

|1=†Posnanskytherium desaguaderoi

|2={{clade

|1=†Pisanodon nazari

|2={{clade

|1=†Pericotoxodon platignathus

|2={{clade

|1={{clade

|1=†Calchaquitherium mixtum

|2=†Mixotoxodon larensis }}

|2={{clade

|1=†Paratrigodon euguii

|2=†Trigodon gaudri }} }}

}} }} }} }} }} }} }} }} }} }} }}

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There has not been a recent taxonomic revision of the genus Toxodon, leaving the number of valid species uncertain.{{Cite journal |last1=Carrillo |first1=Juan D. |last2=Püschel |first2=Hans P. |date=December 2023 |title=Pleistocene South American native ungulates (Notoungulata and Litopterna) of the historical Roth collections in Switzerland, from the Pampean Region of Argentina |journal=Swiss Journal of Palaeontology |language=en |volume=142 |issue=1 |page=28 |bibcode=2023SwJP..142...28C |doi=10.1186/s13358-023-00291-5 |issn=1664-2376 |pmc=10558389 |pmid=37810207 |doi-access=free}}

The species Toxodon chapalmalensis is known from the Pliocene (Montehermosan-Chapadmalalan) of Argentina,{{Cite journal |last1=Tomassini |first1=Rodrigo L. |last2=Montalvo |first2=Claudia I. |last3=Deschamps |first3=Cecilia M. |last4=Manera |first4=Teresa |date=December 2013 |title=Biostratigraphy and biochronology of the Monte Hermoso Formation (early Pliocene) at its type locality, Buenos Aires Province, Argentina |url=http://dx.doi.org/10.1016/j.jsames.2013.08.002 |journal=Journal of South American Earth Sciences |volume=48 |pages=31–42 |bibcode=2013JSAES..48...31T |doi=10.1016/j.jsames.2013.08.002 |issn=0895-9811 |access-date=2 January 2024 |via=Elsevier Science Direct |hdl-access=free |hdl=11336/21606}} while Toxodon platensis, the type species, is known from the Pleistocene. The validity of other potential species like Toxodon darwini Burmeister, 1866, and Toxodon ensenadensis Ameghino, 1887 from the Early Pleistocene of Argentina is uncertain, and the species Toxodon gezi C. Ameghino, 1917 and Toxodon aguirrei Ameghino, 1917 have been considered junior synonyms of Toxodon platensis by recent authors.{{Cite journal |last1=Guérin |first1=Claude |last2=Faure |first2=Martine |date=March 2013 |title=Un nouveau Toxodontidae (Mammalia, Notoungulata) du Pléistocène supérieur du Nordeste du Brésil |url=http://dx.doi.org/10.5252/g2013n1a7 |journal=Geodiversitas |volume=35 |issue=1 |pages=155–205 |doi=10.5252/g2013n1a7 |issn=1280-9659}} Some recent authors have argued that Toxodon gracilis Gervais and Ameghino, 1880, should be recognised as a distinct species from the Pleistocene of the Pampas significantly smaller than T. platensis, with these authors suggesting that T. platensis and T. gracilis represent the only valid species of Toxodon in the Pleistocene of the Pampas region. Other authors have argued that all Pleistocene Toxodon species should be considered synonymous with T. platensis.{{Cite journal |last1=Costamagna |first1=Donato |last2=Ferrero |first2=Brenda S. |last3=Giri |first3=Federico |last4=Ribeiro |first4=Ana María |date=August 2024 |title=Study of the shape and size in lower molars of Toxodon platensis (Mammalia: Toxodontidae) of the Late Pleistocene of South America |url=https://linkinghub.elsevier.com/retrieve/pii/S0016699524000627 |journal=Geobios |language=en |doi=10.1016/j.geobios.2024.05.005}}

The bodyform of Toxodon and other toxodontids have been compared to those of hippopotamuses and rhinoceroses.{{Citation |last1=Cassini |first1=Guillermo H. |title=Paleobiology of Santacrucian native ungulates (Meridiungulata: Astrapotheria, Litopterna and Notoungulata) |date=2012-10-11 |work=Early Miocene Paleobiology in Patagonia |pages=243–286 |editor-last=Vizcaíno |editor-first=Sergio F. |url=https://www.cambridge.org/core/product/identifier/9780511667381%23c19461-14-1/type/book_part |access-date=2023-06-29 |edition=1 |publisher=Cambridge University Press |doi=10.1017/cbo9780511667381.015 |isbn=978-0-511-66738-1 |last2=Cerdeño |first2=Esperanza |last3=Villafañe |first3=Amalia L. |last4=Muñoz |first4=Nahuel A. |editor2-last=Kay |editor2-first=Richard F. |editor3-last=Bargo |editor3-first=M. Susana}} Toxodon platensis is one of the largest known toxodontids and notoungulates, with an estimated body mass of approximately {{Convert|1000-1200|kg|lb}},{{Cite journal |last1=Nelson |first1=Allison |last2=Engelman |first2=Russell K. |last3=Croft |first3=Darin A. |date=September 2023 |title=How to weigh a fossil mammal? South American notoungulates as a case study for estimating body mass in extinct clades |url=https://link.springer.com/10.1007/s10914-023-09669-1 |journal=Journal of Mammalian Evolution |language=en |volume=30 |issue=3 |pages=773–809 |doi=10.1007/s10914-023-09669-1 |issn=1064-7554}} and a body length of around {{Convert|2.7|m}}.Fariña RA, Vizcaíno SF& De Iuliis G. 2012 Megafauna: giant beasts of Pleistocene South America. Bloomington, IN: Indiana University Press. p. 264-265

The skull of Toxodon is proportionally large, and triangular in shape when viewed from above.{{Cite journal |last1=Ferrero |first1=Brenda S. |last2=Schmidt |first2=Gabriela I. |last3=Pérez-García |first3=María I. |last4=Perea |first4=Daniel |last5=Ribeiro |first5=Ana M. |date=2021-08-27 |title=A new Toxodontidae (Mammalia, Notoungulata) from the upper Pliocene–lower Pleistocene of Uruguay |url=https://www.tandfonline.com/doi/full/10.1080/02724634.2021.2023167 |journal=Journal of Vertebrate Paleontology |language=en |volume=41 |issue=5 |doi=10.1080/02724634.2021.2023167 |bibcode=2021JVPal..41E3167F |issn=0272-4634}} All of the teeth in the jaws are high-crowned (hypsodont).Scott WB. [https://www.biodiversitylibrary.org/item/212227#page/175/mode/1up Mammalia of the Santa Cruz Beds. Volume VI, Paleontology. Part II, Toxodontia]. In: Scott WB, editor. Reports of the Princeton University Expeditions to Patagonia, 1896–1899. Stuttgart: Princeton University, E. Schweizerbart’sche Verlagshandlung (E. Nägele); 1912. pp. 211-216 Like other toxodontids, the upper and lower first incisors (I1 and i1) are large and protrude, with the second upper incisors (I2) and lower third incisors (i3) being modified into evergrowing tusks.{{Cite journal |last1=Braunn |first1=Patrícia |last2=Ferigolo |first2=Jorge |last3=Ribeiro |first3=Ana |date=2021 |title=Enamel microstructure of permanent and deciduous teeth of notoungulate Toxodon: development, functional and evolutionary implications |url=http://www.app.pan.pl/article/item/app007722020.html |journal=Acta Palaeontologica Polonica |volume=66 |doi=10.4202/app.00772.2020|doi-access=free }} The upper incisors display an arched shape,S.F. Vizcaino, R.A. Farina, J.C. Fernicola "[https://www.researchgate.net/publication/288069897_Young_Darwin_and_the_ecology_and_extinction_of_Pleistocene_South_American_fossil_mammals#pf4 Young Darwin and the ecology and extinction of Pleistocene South American fossil mammals]" Revista de la Asociacion Geologica Argentina, 64 (2009), pp. 160-169 while the lower incisors project horizontally forwards at the front of the lower jaw. The wide front of the lower jaw with the horizontally-arranged incisors has been described as "spade-like". There is a gap (diastema) between the incisors and the cheek teeth.E. Anderson Who's who in the Pleistocene: a mammalian bestiary P.S. Martin, R.G. Klein (Eds.), Quaternary Extinctions: a Prehistoric Revolution, The University of Arizona Press, Tucson, AZ (1989), pp. 64 Like other derived toxodontids, Toxodon had long, ever-growing (hypselodont) cheek (premolar and molar) teeth,{{Cite journal |last1=Gomes Rodrigues |first1=Helder |last2=Herrel |first2=Anthony |last3=Billet |first3=Guillaume |date=2017-01-31 |title=Ontogenetic and life history trait changes associated with convergent ecological specializations in extinct ungulate mammals |journal=Proceedings of the National Academy of Sciences |language=en |volume=114 |issue=5 |pages=1069–1074 |bibcode=2017PNAS..114.1069G |doi=10.1073/pnas.1614029114 |issn=0027-8424 |pmc=5293108 |pmid=28096389 |doi-access=free}} with the name Toxodon deriving from the curved shape of the upper molars, which are bowed inwards towards the midline of the skull to fit in the upper jaw. Evergrowing cheek teeth are unknown in any living ungulates, but are present in some other mammal groups like wombats and rodents. The surface of the cheek teeth is primarily composed of dentine.

The thoracic vertebrae of Toxodon have elongate neural spines, which likely anchored muscles which supported the large head. The legs of Toxodon are relatively short, with their bones being robust.{{Cite journal |last1=Oliveira |first1=Édison V. |last2=Bélo |first2=Pétrius S. |last3=Fambrini |first3=Gelson L. |last4=Sial |first4=Alcides N. |last5=Silva |first5=Ana K.B. |last6=Barreto |first6=Alcina M.F. |date=October 2019 |title=A new late Pleistocene ichnological site with mammal footprints from Brazil |url=https://linkinghub.elsevier.com/retrieve/pii/S089598111930135X |journal=Journal of South American Earth Sciences |language=en |volume=94 |pages=102216 |doi=10.1016/j.jsames.2019.102216|bibcode=2019JSAES..9402216O }} The hindlimb is considerably longer than the forelimb, resulting in the back being elevated and the shoulder, neck and head being relatively low. The ulna has a strongly backwardly projecting olecranon process similar to that of rhinos, suggesting that the front leg was held extended when standing. The (distal) part of the femur closest to the foot shows a pronounced medial trochlear ridge, which likely served along with the patella (kneecap) to allow the knees to be locked when standing akin to the stay apparatus of living horses as an energy saving mechanism.Shockey BJ. 2001. "[https://www.app.pan.pl/article/item/app46-277.html Specialized knee joints in some extinct, endemic, South American herbivores]" Acta Palaeontologica Polonica 46:277–88 There are three functional digits on each foot, which are tipped with hoof-like phalanges.{{Cite journal |last1=Lorente |first1=Malena |last2=Gelfo |first2=Javier N. |last3=López |first3=Guillermo M. |date=April 2019 |title=First skeleton of the notoungulate mammal Notostylops murinus and palaeobiology of Eocene Notostylopidae |url=https://www.idunn.no/doi/10.1111/let.12310 |journal=Lethaia |language=en |volume=52 |issue=2 |pages=244–259 |doi=10.1111/let.12310 |bibcode=2019Letha..52..244L |issn=0024-1164}}

{{gallery|ToxodonMLP1 (cropped).jpg|Mount at Museo de La Plata, Argentina|Toxodon platensis skull 3.JPG|Skull in front-on view|File:Crani de Toxodon, Museu de Ciències Naturals de València.JPG|Skull in oblique view|Em - Toxodon platensis - 1.jpg|Skeleton in side-on view|Cráneo de Toxodon.jpg|Skull in side-on view|||||||width=200|height=180|align=center}}

Toxodon had a widespread distribution in South America east of the Andes, ranging from northern Argentina and Bolivia to the western Amazon on the Peru-Brazil border, to Northeast Brazil. Although some authors suggest that the distribution of Toxodon extended into Venezuela, other authors suggest that the related Mixotoxodon (which ranged as far north as the southern United States) was the only toxodontid present in the region during the Pleistocene.{{Cite journal |last1=Carrillo-Briceño |first1=Jorge Domingo |last2=Amson |first2=Eli |last3=Zurita |first3=Alfredo |last4=Sánchez-Villagra |first4=Marcelo Ricardo |date=2016-12-12 |title=Hermann Karsten (1817–1908): a German naturalist in the Neotropics and the significance of his paleovertebrate collection |url=https://fr.copernicus.org/articles/20/21/2016/ |journal=Fossil Record |language=en |volume=20 |issue=1 |pages=21–36 |doi=10.5194/fr-20-21-2016 |doi-access=free |bibcode=2016FossR..20...21C |issn=2193-0074|hdl=11336/81200 |hdl-access=free }}

File:A-Pleistocene-meso-megamammals-from-Sergipe-Brazil.jpg (foreground right), the glyptodonts Glyptotherium and Panochthus, the pampathere Holmesina paulacoutoi (midground centre-left) and the armadillo Pachyarmatherium brasiliense (foreground left)]]

Although some authors have suggested that Toxodon was semiaquatic based on the similarity of some aspects of its anatomy to hippopotamuses, this has been disputed by other authors, and analysis of oxygen isotope ratios (which differ between terrestrial and aquatic animals) suggests a terrestrial lifestyle for Toxodon.{{Cite journal |last1=Lopes |first1=Renato P. |last2=Ribeiro |first2=Ana Maria |last3=Dillenburg |first3=Sérgio Rebello |last4=Schultz |first4=Cesar Leandro |date=January 2013 |title=Late middle to late Pleistocene paleoecology and paleoenvironments in the coastal plain of Rio Grande do Sul State, Southern Brazil, from stable isotopes in fossils of Toxodon and Stegomastodon |url=https://linkinghub.elsevier.com/retrieve/pii/S0031018212006293 |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |language=en |volume=369 |pages=385–394 |doi=10.1016/j.palaeo.2012.10.042|bibcode=2013PPP...369..385L }} As such, it has been suggested that Toxodon was probably more ecologically comparable to rhinoceroses.

Toxodon is suggested to have been capable of moving at considerable speed. Toxodon is believed to have been ecologically plastic and have had a wide niche breadth,{{Cite journal |last1=Dantas |first1=Mário André Trindade |last2=Cherkinsky |first2=Alexander |last3=Bocherens |first3=Hervé |last4=Drefahl |first4=Morgana |last5=Bernardes |first5=Camila |last6=França |first6=Lucas de Melo |date=15 August 2017 |title=Isotopic paleoecology of the Pleistocene megamammals from the Brazilian Intertropical Region: Feeding ecology (δ13C), niche breadth and overlap |url=https://www.sciencedirect.com/science/article/pii/S0277379117300616 |journal=Quaternary Science Reviews |volume=170 |pages=152–163 |doi=10.1016/j.quascirev.2017.06.030 |issn=0277-3791 |access-date=2 January 2024 |via=Elsevier Science Direct}} with its diet varying according to local conditions,{{Cite journal |last1=Pansani |first1=Thaís Rabito |last2=Muniz |first2=Fellipe Pereira |last3=Cherkinsky |first3=Alexander |last4=Pacheco |first4=Mírian Liza Alves Forancelli |last5=Dantas |first5=Mário André Trindade | name-list-style = vanc |date=October 2019|title=Isotopic paleoecology (δ13C, δ18O) of Late Quaternary megafauna from Mato Grosso do Sul and Bahia States, Brazil |url=https://linkinghub.elsevier.com/retrieve/pii/S0277379119302926 |journal=Quaternary Science Reviews |language=en |volume=221 |pages=105864 |doi=10.1016/j.quascirev.2019.105864 |bibcode=2019QSRv..22105864P |s2cid=202200336 }} with an almost totally C₃ browsing diet in the Amazon rainforest, mixed feeding C₃ in Bahia and the Pampas, and an almost completely C₄ dominated grazing diet in the Chaco.{{Cite journal |last=MacFadden |first=Bruce J. |name-list-style=vanc |date=September 2005 |title=Diet and habitat of toxodont megaherbivores (Mammalia, Notoungulata) from the late Quaternary of South and Central America |url=http://linkinghub.elsevier.com/retrieve/pii/S0033589405000712 |journal=Quaternary Research |language=en |volume=64 |issue=2 |pages=113–124 |bibcode=2005QuRes..64..113M |doi=10.1016/j.yqres.2005.05.003 |access-date=2 January 2024 |via=Elsevier Science Direct}} Within the Brazilian Intertropical Region (BIR), T. platensis was a mixed feeder;{{Cite journal |last=Andrade |first=Luana Cardoso de |last2=Dantas |first2=Mário André Trindade |last3=Oliveira |first3=Édison Vicente |date=15 July 2024 |title=Tracking the past: Isotopic paleoecology (δ13C, δ18O) of the Late Pleistocene megafauna from northeast of South America |url=https://www.sciencedirect.com/science/article/pii/S0895981124001391?casa_token=qLcs1buwqXkAAAAA:ZIHLtF23TcC75dts2dusZHvPUG6tyb-uAfAT8Ng2gZM5elZYP_YsUAJJrpaMoWMMU-I2Ibw6-10 |journal=Journal of South American Earth Sciences |language=en |volume=140 |pages=104917 |doi=10.1016/j.jsames.2024.104917 |access-date=19 March 2025 |via=Elsevier Science Direct}} seasonal variations in the BIR had little impact on the diet of T. platensis.{{Cite journal |last1=Gomes |first1=Verônica Santos |last2=Lessa |first2=Carlos Micael Bonfim |last3=Oliveira |first3=Gustavo Ribeiro de |last4=Bantim |first4=Renan Alfredo Machado |last5=Sayão |first5=Juliana |last6=Bocherens |first6=Hervé |last7=Araújo-Júnior |first7=Hermínio Ismael de |last8=Dantas |first8=Mário André Trindade |date=January 2023 |title=Seasonal variations in diet (δ13C) and climate (δ 18O) inferred through toxodonts enamel teeth during the Late Pleistocene in the brazilian intertropical region |url=https://linkinghub.elsevier.com/retrieve/pii/S0895981122004345 |journal=Journal of South American Earth Sciences |language=en |volume=121 |pages=104148 |doi=10.1016/j.jsames.2022.104148 |access-date=19 April 2024 |via=Elsevier Science Direct}} Although Toxodon is thought to have inhabited open landscapes like steppe and savannah,{{Cite journal |last1=Dantas |first1=Mário André Trindade |last2=Dutra |first2=Rodrigo Parisi |last3=Cherkinsky |first3=Alexander |last4=Fortier |first4=Daniel Costa |last5=Kamino |first5=Luciana Hiromi Yoshino |last6=Cozzuol |first6=Mario Alberto |last7=Ribeiro |first7=Adauto de Souza |last8=Vieira |first8=Fabiana Silva |date=January 2013 |title=Paleoecology and radiocarbon dating of the Pleistocene megafauna of the Brazilian Intertropical Region |url=https://www.cambridge.org/core/product/identifier/S0033589400002945/type/journal_article |journal=Quaternary Research |language=en |volume=79 |issue=1 |pages=61–65 |doi=10.1016/j.yqres.2012.09.006 |bibcode=2013QuRes..79...61D |issn=0033-5894}}{{Cite journal |last1=Lopes |first1=Renato Pereira |last2=Scherer |first2=Carolina Saldanha |last3=Pereira |first3=Jamil Corrêa |last4=Dillenburg |first4=Sérgio Rebello |date=July 2023 |title=Paleoenvironmental changes in the Brazilian Pampa based on carbon and oxygen stable isotope analysis of Pleistocene camelid tooth enamel |url=https://onlinelibrary.wiley.com/doi/10.1002/jqs.3502 |journal=Journal of Quaternary Science |language=en |volume=38 |issue=5 |pages=702–718 |doi=10.1002/jqs.3502 |bibcode=2023JQS....38..702L |issn=0267-8179}} in some areas like the southwestern Brazilian Amazon, it is suggested to have inhabited woodland.{{Cite journal |last1=Asevedo |first1=Lidiane |last2=Ranzi |first2=Alceu |last3=Kalliola |first3=Risto |last4=Pärssinen |first4=Martti |last5=Ruokolainen |first5=Kalle |last6=Cozzuol |first6=Mário Alberto |last7=Nascimento |first7=Ednair Rodrigues do |last8=Negri |first8=Francisco Ricardo |last9=Souza-Filho |first9=Jonas P. |last10=Cherkinsky |first10=Alexander |last11=Trindade Dantas |first11=Mário André |date=January 2021 |title=Isotopic paleoecology (δ13C, δ18O) of late Quaternary herbivorous mammal assemblages from southwestern Amazon |url=https://linkinghub.elsevier.com/retrieve/pii/S0277379120306624 |journal=Quaternary Science Reviews |language=en |volume=251 |pages=106700 |doi=10.1016/j.quascirev.2020.106700}}{{Cite journal |last1=Chahud |first1=Artur |last2=de Oliveira Costa |first2=Paulo Ricardo |last3=Ferreira Figueiredo |first3=Gisele |last4=Okumura |first4=Mercedes |date=January 2023 |title=Quaternary ungulates of the Abismo Ponta de Flecha Cave, Ribeira of Iguape Valley, Southeast Brazil: Zooarchaeological and Paleoenvironmental aspects |url=https://linkinghub.elsevier.com/retrieve/pii/S0895981122003935 |journal=Journal of South American Earth Sciences |language=en |volume=121 |pages=104107 |doi=10.1016/j.jsames.2022.104107|bibcode=2023JSAES.12104107C }}

Like living animals of similar size, it has been suggested that Toxodon probably only gave birth to a single offspring at a time.{{Cite journal |last=Andrea |first=Elissamburu |date=July 2016 |title=Prediction of offspring in extant and extinct mammals to add light on paleoecology and evolution |url=https://linkinghub.elsevier.com/retrieve/pii/S0031018216300542 |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |language=en |volume=453 |pages=73–79 |doi=10.1016/j.palaeo.2016.03.033|bibcode=2016PPP...453...73A |hdl=11336/54314 |hdl-access=free }}

T. platensis bones have been found displaying signs of disease like osteomyelitis and spondyloarthropathies.{{Cite journal |last1=Luna |first1=Carlos A. |last2=De S. Barbosa |first2=Fernando H. |last3=Gonzalez |first3=Romina |last4=Miño-Boilini |first4=Ángel R. |last5=Repetto |first5=Carolina |last6=Zurita |first6=Alfredo E. |date=7 February 2024 |title=Bone diseases in a Pleistocene South American native ungulate species: the case of Toxodon platensis Owen, 1837 (Mammalia, Notoungulata, Toxodontidae) |url=https://onlinelibrary.wiley.com/doi/10.1002/jqs.3601 |journal=Journal of Quaternary Science |volume=39 |issue=8 |pages=1206–1215 |language=en |doi=10.1002/jqs.3601 |issn=0267-8179 |access-date=28 March 2024 |via=Wiley Online Library}} The teeth of Toxodon often display enamel hypoplasia (loss of tooth enamel) in the form of grooves and pits, which is likely due to their evergrowing nature and/or environmental stresses.{{Cite journal |last=Braunn |first=Patrícia R. |last2=Ribeiro |first2=Ana M. |last3=Ferigolo |first3=Jorge |date=July 2014 |title=Microstructural defects and enamel hypoplasia in teeth of Toxodon Owen, 1837 from the Pleistocene of Southern Brazil |url=https://www.idunn.no/doi/10.1111/let.12063 |journal=Lethaia |language=en |volume=47 |issue=3 |pages=418–431 |doi=10.1111/let.12063 |issn=0024-1164}}

Tracks probably attributable to Toxodon have been reported from eastern Pernambuco in Northeast Brazil.

Isotopic analysis suggests that Toxodon may have been predated upon by the large sabertooth cat Smilodon populator, the apex predator of South American ecosystems during much of the Pleistocene.{{Cite journal |last1=Dantas |first1=Mário André Trindade |last2=Cherkinsky |first2=Alexander |last3=Lessa |first3=Carlos Micael Bonfim |last4=Santos |first4=Luciano Vilaboim |last5=Cozzuol |first5=Mario Alberto |last6=Omena |first6=Érica Cavalcante |last7=Silva |first7=Jorge Luiz Lopes |last8=Sial |first8=Alcides Nóbrega |last9=Bocherens |first9=Hervé |date=2020-07-14 |title=Isotopic paleoecology (δ13C, δ18O) of a late Pleistocene vertebrate community from the Brazilian Intertropical Region |journal=Revista Brasileira de Paleontologia |language=en |volume=23 |issue=2 |pages=138–152 |doi=10.4072/rbp.2020.2.05 |issn=2236-1715 |doi-access=free}}

Toxodon and the other remaining toxodontids became extinct at the end of the Late Pleistocene around 12,000 years as part of the end-Pleistocene extinction event alongside almost all other large animals in South America. mid-Holocene dates for Toxodon and Pampas other megafauna have been questioned and are suggested to be the result of contamination.{{cite journal |vauthors=Politis GG, Messineo PG, Stafford TW, Lindsey EL |date=March 2019 |title=Campo Laborde: A Late Pleistocene giant ground sloth kill and butchering site in the Pampas |journal=Science Advances |volume=5 |issue=3 |pages=eaau4546 |bibcode=2019SciA....5.4546P |doi=10.1126/sciadv.aau4546 |pmc=6402857 |pmid=30854426}} These extinctions followed the first arrival of humans in the Americas, and it has been suggested human hunting may have been a casual factor in the extinctions. Several sites record apparent interactions between Toxodon and humans. Remains of Toxodon from the Arroyo Seco 2 site in the Pampas are associated with unambiguously butchered megafauna, but it is unclear if the Toxodon itself was actually butchered or the remains were naturally transported to the site.{{cite journal |vauthors=Politis GG, Gutiérrez MA, Rafuse DJ, Blasi A |date=28 September 2016 |title=The Arrival of Homo sapiens into the Southern Cone at 14,000 Years Ago |journal=PLOS ONE |volume=11 |issue=9 |pages=e0162870 |bibcode=2016PLoSO..1162870P |doi=10.1371/journal.pone.0162870 |pmc=5040268 |pmid=27683248 |doi-access=free |veditors=Petraglia MD}} At the Paso Otero 5 site in the Pampas of northeast Argentina, burned bones of Toxodon alongside those of numerous other extinct megafauna species are associated with Fishtail points (a type of knapped stone spear point common across South America at the end of the Pleistocene, suggested to be used to hunt large mammals{{Cite journal |last1=Prates |first1=Luciano |last2=Rivero |first2=Diego |last3=Perez |first3=S. Ivan |date=2022-10-25 |title=Changes in projectile design and size of prey reveal the central role of Fishtail points in megafauna hunting in South America |journal=Scientific Reports |language=en |volume=12 |issue=1 |page=16964 |bibcode=2022NatSR..1216964P |doi=10.1038/s41598-022-21287-0 |issn=2045-2322 |pmc=9596454 |pmid=36284118}}). The bones of the megafauna were probably deliberately burned as fuel. No cut marks are visible on the vast majority of bones at the site (with only one bone of a llama possibly displaying any butchery marks), which may be due to the burning degrading the bones.G. Martínez, M. A. Gutiérrez, [https://www.researchgate.net/publication/255171250_Paso_Otero_5_a_summary_of_the_interdisciplinary_lines_of_evidence_for_reconstructing_early_human_occupation_and_paleoenvironment_in_the_Pampean_region_Argentina Paso Otero 5: A summary of the interdisciplinary lines of evidence for reconstructing early human occupation and paleoenvironment in the Pampean region, Argentina], in Peuplements et Préhistoire de l’Amérique, D. Vialou, Ed. (Muséum National d’ Histoire Naturelle. Departement de Prehistoire, U.M.R, Paris, 2011), pp. 271–284. Various remains of Toxodon platensis in the collection of the Museum national d'Histoire naturelle collected from the Pampas region in the 19th century including a femur, an iliac fragment, a tibia, as well as a mandible (the latter of which has been radiocarbon dated to around 13,000 years ago), have been found to display cut marks indicative of butchery.{{Cite journal |last=Toledo |first=Marcelo Javier |date=April 2023 |title=Anthropic modifications on megafauna bones in the paleontological collections of the Museum national d'Histoire naturelle de Paris: Historical aspects and implications for the Pampean Pleistocene peopling |url=https://linkinghub.elsevier.com/retrieve/pii/S0003552123000195 |journal=L'Anthropologie |language=en |volume=127 |issue=2 |pages=103134 |doi=10.1016/j.anthro.2023.103134}}

{{Reflist}}

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• {{cite book | first1 = Barry | last1 = Cox | first2 = Colin | last2 = Harrison | first3 = R.J.G. | last3 = Savage | first4 = Brian | last4 = Gardiner | name-list-style = vanc | title = The Simon & Schuster Encyclopedia of Dinosaurs and Prehistoric Creatures: A Visual Who's Who of Prehistoric Life | url = https://archive.org/details/simonschusterenc00coxb | url-access = registration | publisher = Simon & Schuster | date = October 1999 | isbn = 978-0-684-86411-2 }}

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{{Meridiungulata|N.|state=collapsed}}

{{Taxonbar|from=Q131467}}

Category:Toxodonts

Category:Miocene genus first appearances

Category:Holocene extinctions

Category:Miocene mammals of South America

Category:Pliocene mammals of South America

Category:Pleistocene mammals of South America

Category:Lujanian

Category:Ensenadan

Category:Uquian

Category:Chapadmalalan

Category:Montehermosan

Category:Huayquerian

Category:Chasicoan

Category:Mayoan

Category:Neogene Argentina

Category:Ituzaingó Formation

Category:Sopas Formation

Category:Pleistocene Argentina

Category:Pleistocene Bolivia

Category:Pleistocene Brazil

Category:Pleistocene Paraguay

Category:Dolores Formation, Uruguay

Category:Fossils of Argentina

Category:Fossils of Bolivia

Category:Fossils of Brazil

Category:Fossils of Paraguay

Category:Fossils of Uruguay

Category:Fossil taxa described in 1837

Category:Taxa named by Richard Owen

Category:Prehistoric placental genera