Toxodon

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Toxodon
Temporal range: Late Miocene-Holocene (Serravallian-Greenlandian)
11.6–0.011 Ma
Toxodon skeleton in BA.JPG
Skeleton of Toxodon in Buenos Aires
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Notoungulata
Family: Toxodontidae
Subfamily: Toxodontinae
Genus: Toxodon
Owen, 1837
Type species
Toxodon platensis
Owen, 1837
Other species
  • T. burmeisteri Giebel, 1866
  • T. chapalmalensis Ameghino, 1908
  • T. darwini Burmeister, 1866
  • T. ensenadensis Ameghino, 1887
  • T. expansidens Cope, 1886
  • T. gracilis Gervais and Ameghino, 1880
Synonyms

Genus-level

  • Dilobodon Ameghino, 1886
  • Chapalmalodon Pascual, 1957
  • Chapadmalodon Tonni et al., 1992 (lapsus calami)

T. platensis

  • T. angustidens Owen, 1846
  • T. owenii Burmeister, 1866
  • T. gervaisii Gervais & Ameghino, 1880
  • T. aguirrei Ameghino, 1917
  • T. gezi Ameghino, 1917

T. burmeisteri

  • T. paradoxus Ameghino, 1882
  • T. protoburmeisteri Ameghino, 1887
  • T. bilobidens Ameghino, 1887

T. chapalmalensis

  • Chapalmalodon chapalmalensis Pascual, 1957
  • T. chapadmalensis Cione & Tonni, 1995 (lapsus calami)
  • T. chapalmalalensis Oliva & Cerdeno, 2007 (lapsus calami)

T. ensenadensis

  • T. giganteus Moreno, 1888
  • T. elongatus Roth, 1898

T. gracilis

  • T. voghti Moreno, 1888

Toxodon (meaning "bow tooth" in reference to the curvature of the teeth) is an extinct genus of South American mammals from the Late Miocene to early Holocene epochs (Mayoan to Lujanian in the SALMA classification) (about 11.6 million to 11,000 years ago).[1][2] It is a member of Notoungulata, one of several now extinct orders of hoofed mammals indigenous to South America distinct from living perissodactyls and artiodactyls. It was among the largest and last members of its order, and was probably the most common large hoofed mammal in South America of its time.

Taxonomy[edit]

Skeletal diagram

Toxodon was one of the last members of Notoungulata, a group of ungulates that had been part of the fauna of South America since the Paleocene. Toxodon was a member of Toxodontidae a large bodied group including similar, vaguely rhinoceros like forms.

Charles Darwin was one of the first to collect Toxodon fossils, after paying 18 pence for a T. platensis skull from a farmer in Uruguay.[3] In 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."[4] 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,

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!

Analysis of collagen sequences obtained from Toxodon as well as from Macrauchenia found that South America's native notoungulates and litopterns form a sister group to perissodactyls, making them true ungulates.[5][6] This finding has been corroborated by an analysis of mitochondrial DNA extracted from a Macrauchenia fossil, which yielded a date of 66 Ma for the time of the split with perissodactyls.[7]

Evolution[edit]

In 2014, a study identifying a new species of toxodontid resolved the phylogenetic relations of the toxodontids, including to Toxodon. The below cladogram was found by the study:[8]

   †Notoungulata   

Pampahippus arenalesi

Rhynchippus spp.

Scarrittia canquelensis

Leonitinia gaudri

  †Toxodontidae  

Proadinotherium leptognathum

Adinotherium spp.

Nesodon taweretus

Nesodon imbricatus

Palyeidodon obtusum

Hyperoxotodon speciosus

Nonotherium henningi

Xotodon spp.

Andinotoxodon bolivariensis

Dinotoxodon paranensis

Toxodon platensis

Gyrinodon quassus

Ocnerotherium intermedium

Hoffstetterius imperator

Posnanskytherium desaguaderoi

Pisanodon nazari

Pericotoxodon platignathus

Calchaquitherium mixtum

Mixotoxodon larensis

Paratrigodon euguii

Trigodon gaudri

Description[edit]

Toxodon was about 2.7 m (8 ft 10 in) in body length, with an estimated weight up to 1,415 kg (3,120 lb)[9] and about 1.5 m (4 ft 11 in) high at the shoulder and resembled a heavy rhinoceros, with a short and vaguely hippopotamus-like head.[10] Because of the position of its nasal openings, it is believed that Toxodon had a well-developed snout.[citation needed] Toxodon possessed a large, barrel shaped body.[11] It had short stout legs with plantigrade feet with three functional relatively short toes.[11] The hind limbs are longer and raised higher than the front limbs, giving a sloped appearance to the body.[11] Like horses, it had a stay apparatus allowing the knees to be passively locked while standing.[12]

The vertebrae were equipped with high apophyses, which most likely supported the massive weight and muscles as well as its powerful head.[citation needed] Toxodon had broad jaws which were filled with bow shaped teeth and incisors.[13] The teeth of Toxodon have no roots and are ever-growing (euhypsodont) like those of rodents and lagomorphs, and often exhibit enamel hypoplasia.[14]

Palaeobiology[edit]

Toxodon skull in front view

It was initially believed to have been amphibious, but after examining the proportions of the femur and tibia, as well as the position of its head, below the top of the spinal column, palaeontologists realized that it had features similar to terrestrial animals such as elephants or rhinoceroses. The fossils are also usually found in arid and semi-arid areas, typically an indication of a primarily terrestrial life.[citation needed]

Toxodon would have had a very unusual gait, due to its peculiar proportions. It may have galloped to escape predators, but like a rhino, it probably relied more on its size as protection.[citation needed]

Toxodon is believed to have been ecologically plastic, with its diet varying according to local conditions,[15] with an almost totally C3 browsing diet in the Amazon rainforest, mixed feeding C3 in Bahia and the Pampas to almost completely C4 dominated grazing diet in the Chaco.[16]

Extinction[edit]

Toxodon became extinct at the beginning of the Holocene as part of the Quaternary extinction event, alongside almost all other large animals in South America. Previous mid-Holocene dates are now thought to be in error.[17] Remains from the Arroyo Seco 2 site in the Pampas have been interpreted to be the result of butchery, suggesting that human hunting was a contributing factor to extinction.[18]

Restoration of T. platensis
Toxodon skull, Zoologisk Museum, Copenhagen

Distribution[edit]

Restoration of Toxodon platensis

Toxodon has a wide distribution in South America during the Late Pleistocene, extending from the Pampas into the Amazon rainforest.

Fossils of Toxodon have been found in:[2][19]

Holocene
Pleistocene
Miocene-Pliocene (Montehermosan)
Miocene

References[edit]

  1. ^ Baffa O, Brunetti A, Karmann I, Neto CM (May 2000). "ESR dating of a toxodon tooth from a Brazilian karstic cave". Applied Radiation and Isotopes. 52 (5): 1345–9. doi:10.1016/S0969-8043(00)00093-2. PMID 10836452.
  2. ^ a b Turvey ST (28 May 2009). Holocene Extinctions. OUP Oxford. ISBN 978-0-19-157998-1.
  3. ^ Quammen, D. (February 2009). "Darwin's first clues". National Geographic. p. 45.
  4. ^ Darwin, Charles (1997) [1839]. Browne, J.; Neve, M. (eds.). The Voyage of the Beagle. ISBN 978-0-14-043268-8. Read, 19th April 1837. A detailed account will appear in the first part of the zoology of Voyage of the Beagle.
  5. ^ Welker F, Collins MJ, Thomas JA, Wadsley M, Brace S, Cappellini E, et al. (June 2015). "Ancient proteins resolve the evolutionary history of Darwin's South American ungulates". Nature. 522 (7554): 81–4. Bibcode:2015Natur.522...81W. doi:10.1038/nature14249. PMID 25799987. S2CID 4467386.
  6. ^ Buckley, M. (7 May 2015). "Ancient collagen reveals evolutionary history of the endemic South American 'ungulates'". Proceedings of the Royal Society B: Biological Sciences. 282 (1806): 20142671. doi:10.1098/rspb.2014.2671. PMC 4426609. PMID 25833851.
  7. ^ Westbury M, Baleka S, Barlow A, Hartmann S, Paijmans JL, Kramarz A, et al. (June 2017). "A mitogenomic timetree for Darwin's enigmatic South American mammal Macrauchenia patachonica". Nature Communications. 8: 15951. Bibcode:2017NatCo...815951W. doi:10.1038/ncomms15951. PMC 5490259. PMID 28654082.
  8. ^ Forasiepi AM, Cerdeno E, Bond M, Schmidt GI, Naipauer M, Straehl FR, et al. (2014). "New toxodontid (Notoungulata) from the Early Miocene of Mendoza, Argentina". Paläontologische Zeitschrift. 89 (3): 611–634. doi:10.1007/s12542-014-0233-5. S2CID 129293436.
  9. ^ Fariña RA, Czerwonogora A, di Giacomo M (March 2014). "Splendid oddness: revisiting the curious trophic relationships of South American Pleistocene mammals and their abundance". Anais da Academia Brasileira de Ciencias. 86 (1): 311–31. doi:10.1590/0001-3765201420120010. PMID 24676170.
  10. ^ Fariña RA, Vizcaíno SF, de Iuliis G (2012). Megafauna: Giant Beasts of Pleistocene South America. Indiana University Press. ISBN 978-0-253-00230-3.
  11. ^ a b c Defler T (2019), "The Native Ungulates of South America (Condylarthra and Meridiungulata)", History of Terrestrial Mammals in South America, Topics in Geobiology, Cham: Springer International Publishing, 42, p. 102, doi:10.1007/978-3-319-98449-0_5, ISBN 978-3-319-98448-3, retrieved 10 July 2020
  12. ^ Shockey BJ. 2001. "Specialized knee joints in some extinct, endemic, South American herbivores" Acta Palaeontologica Polonica 46:277–88
  13. ^ Croft DA, Gelfo JN, López GM (30 May 2020). "Splendid Innovation: The Extinct South American Native Ungulates". Annual Review of Earth and Planetary Sciences. 48 (1): 259–290. Bibcode:2020AREPS..48..259C. doi:10.1146/annurev-earth-072619-060126. ISSN 0084-6597.
  14. ^ Braunn PR, Ribeiro AM, Ferigolo J (July 2014). "Microstructural defects and enamel hypoplasia in teeth of Toxodon Owen, 1837 from the Pleistocene of Southern Brazil". Lethaia. 47 (3): 418–431. doi:10.1111/let.12063.
  15. ^ Pansani TR, Muniz FP, Cherkinsky A, Pacheco ML, Dantas MA (October 2019). "Isotopic paleoecology (δ13C, δ18O) of Late Quaternary megafauna from Mato Grosso do Sul and Bahia States, Brazil". Quaternary Science Reviews. 221: 105864. Bibcode:2019QSRv..22105864P. doi:10.1016/j.quascirev.2019.105864.
  16. ^ MacFadden BJ (September 2005). "Diet and habitat of toxodont megaherbivores (Mammalia, Notoungulata) from the late Quaternary of South and Central America". Quaternary Research. 64 (2): 113–124. Bibcode:2005QuRes..64..113M. doi:10.1016/j.yqres.2005.05.003.
  17. ^ Politis GG, Messineo PG, Stafford TW, Lindsey EL (March 2019). "Campo Laborde: A Late Pleistocene giant ground sloth kill and butchering site in the Pampas". Science Advances. 5 (3): eaau4546. Bibcode:2019SciA....5.4546P. doi:10.1126/sciadv.aau4546. PMC 6402857. PMID 30854426.
  18. ^ Politis GG, Gutiérrez MA, Rafuse DJ, Blasi A (28 September 2016). Petraglia MD (ed.). "The Arrival of Homo sapiens into the Southern Cone at 14,000 Years Ago". PLOS ONE. 11 (9): e0162870. Bibcode:2016PLoSO..1162870P. doi:10.1371/journal.pone.0162870. PMC 5040268. PMID 27683248.
  19. ^ Toxodon at Fossilworks.org

Further reading[edit]