Editing Mylodon

{{Short description|Extinct genus of mylodontid ground sloths}}
{{Speciesbox
| fossil_range = [[Pleistocene|Early Pleistocene]]-[[Holocene|Early Holocene]]<br>~{{fossil range|0.781|0.01}} ([[Uquian]]-[[Lujanian]])
| image = Mylodon skull (cropped).jpg
| image_caption = Lithograph of the skull of ''Mylodon''
| display_parents = 2
| genus = Mylodon
| parent_authority = [[Richard Owen|Owen]], 1840
| species = darwini
| authority = [[Richard Owen|Owen]], 1840
}}

'''''Mylodon''''' is an extinct [[genus]] of [[ground sloth]] belonging to the family [[Mylodontidae]], known from southern South America. With a total length of 3 to 4 m and a body mass of 1-2 tonnes, it is one of the largest mylodontids (though it was considerably exceeded in size by the mylodontid ''[[Lestodon]]'').

The oldest finds probably date to the Lower [[Pleistocene]]; however, most of the fossil remains date to the [[Late Pleistocene]]. Its distribution ranged from southern [[Bolivia]] and the [[Pampas]] in the north southwards to the southernmost part of [[Patagonia]] at around [[52nd parallel south|52]]-[[53rd parallel south|53]] degrees south, the furthest south of any Pleistocene ground sloth, with some of the best known remains of the species being from the eponymous [[Cueva del Milodon]] (cave of ''Mylodon'') in southern Chile. 

In addition to skeletal remains, ''Mylodon'' is also known from preserved skin and hair. Preserved dung ([[Coprolite|coprolites]]) indicates that ''Mylodon'' was a primarily a [[Grazing (behaviour)|grazer]], feeding on [[grasses]] and [[sedges]].

''Mylodon'' has generally only a single recognised species, ''Mylodon darwini'', which was described by [[Richard Owen]] in 1840 based on remains collected in the Pampas by [[Charles Darwin]] (for whom the species is named) during the [[Second voyage of HMS Beagle|Voyage of the Beagle]]. Some recent authors suggest that there were two species, with ''M. darwini'' restricted to the Pampas, with the Patagonian remains belonging to the separate species ''Mylodon listai.''<ref name=":0">{{Cite journal |last1=Brambilla |first1=Luciano |last2=Haro |first2=José Augusto |date=2023-11-02 |title=A comparative study of the postcranial skeleton of Patagonian and Pampean specimens of the Pleistocene giant sloth genus Mylodon Owen, 1839 (Xenarthra, Pilosa) and its implications |url=https://www.tandfonline.com/doi/full/10.1080/08912963.2022.2132157 |journal=Historical Biology |language=en |volume=35 |issue=11 |pages=2045–2054 |doi=10.1080/08912963.2022.2132157 |bibcode=2023HBio...35.2045B |issn=0891-2963}}</ref>

''Mylodon'' went extinct at the end of the Late Pleistocene-beginning of the Holocene, around 12-10,000 years ago, as part of the [[Late Pleistocene extinctions|end-Pleistocene extinction event]], along with other ground sloths and most large animals across the Americas. ''Mylodon'' chronologically overlapped with [[Paleo-Indians|Paleoindians]], the first humans to inhabit the Americas, evidence from several sites suggest that they may have hunted ''Mylodon''. The extinction of ''Mylodon'' may be the result of climatic change, hunting by Paleoindians, or a combination of both factors.

== Discovery ==
''Mylodon'' was named by [[Richard Owen]] on the basis of a nearly complete lower jaw with teeth, which was found by [[Charles Darwin]] in a consolidated gravel cliff at [[Bahía Blanca]]<!--date unclear, could be 1832 in 1834-->, during [[Second voyage of HMS Beagle#Fossil finds|the survey expedition of HMS ''Beagle'']].<ref>{{aut|R. Owen}} (1840). Zoology of the Voyage of the Beagle.  Part 1, Fossil Mammalia.  Pp. [http://darwin-online.org.uk/content/frameset?viewtype=text&itemID=F8.7&pageseq=27 63]-[http://darwin-online.org.uk/content/frameset?viewtype=text&itemID=F8.8&pageseq=8 73].</ref> At several sites, preserved hide and dung have been discovered, and are in such a state of conservation that the people who first discovered them believed they belonged to a living animal, instead of to an extinct species. The discovery of fresh-looking samples of skin and dung sparked a small wave of expeditions during the early 20th century to search for a living example of the animal.<ref name="PATAGONIA">{{cite news|date=20 December 1902|title=Patagonia; Hesketh-Prichard's Stirring Tale of Exploration in the Far South|newspaper=The New York Times|url=https://www.nytimes.com/1902/12/20/archives/patagonia-heskethprichards-stirring-tale-of-exploration-in-the-far.html|access-date=2008-11-22}}</ref> The samples have since been found to be around 10,000 years old, although they look fresh because of the extreme cold and stable conditions in the caves in which they were found. 

Well preserved samples of ''Mylodon'' remains have been discovered in the [[Cueva del Milodón]] site in [[Patagonia]], [[Chile]] along the southern flank of [[Cerro Benítez]] in the year 1896. Associated with bones of other early Patagonian animals, these remains of ''Mylodon'' date from an era earlier than 10,000 BC.<ref>[http://www.megalithic.co.uk/article.php?sid=18820 C. Michael Hogan (2008) ''Cueva del Milodon'', Megalithic Portal]</ref> The [[American Museum of Natural History]] has exhibited a sample of ''Mylodon'' dung from Argentina with a note that reads "deposited by [[Theodore Roosevelt]]".<ref name="Bell2002" /><ref name="TRCenter">{{cite web|last=Roosevelt|first=T.R.|date=1915-01-04|title=Letter from Theodore Roosevelt to George Herbert Sherwood|url=https://www.theodorerooseveltcenter.org/Research/Digital-Library/Record?libID=o211307|access-date=2019-10-12|website=theodorerooseveltcenter.org|publisher=[[Dickinson State University]]}}</ref><ref name="AMNH">{{cite web|title=Roosevelt Collections|url=https://www.amnh.org/exhibitions/permanent/south-american-peoples/roosevelt-collection|access-date=2019-10-12|website=amnh.org/exhibitions|publisher=[[American Museum of Natural History|AMNH]]}}</ref><ref name="Warren2015">{{cite web|last=Warren|first=D.|date=2016-05-28|title=The ground sloth|url=https://www.davidwarrenonline.com/2015/05/28/the-ground-sloth/|access-date=2019-10-12|website=Essays in Idleness}}</ref>

== Description ==
=== General ===
[[File:Mylodon size comparison.png|thumb|Size comparison of ''Mylodon darwini'' compared to a human]]
''Mylodon'' was a large representative of the [[Mylodontidae]]. Its total length was estimated to be around 3 to 4 m. Based on the size of the skull, a weight between 1 and 2 tonnes is assumed, with an approximate estimate of 1.65 tonnes.<ref name="christiansenfarina2003">{{cite book |last1=Christiansen |first1=Per |last2=Fariña |first2=Richard A. |chapter=Mass estimation of two fossil ground sloths (Mammalia, Xenarthra, Mylodontidae) |pages=95–101 |chapter-url=https://www.researchgate.net/publication/292021908 |editor1-last=Farina |editor1-first=R. A. |title=Morphological Studies in Fossil and Extant Xenarthra (Mammalia) |series=Senckenbergiana biologica |volume=83 |issue=1 |date=2003 |publisher=E. Schweizerbartsche Verlagsbuchhandlung |isbn=978-3-510-61358-8 }}</ref> Thus, ''Mylodon'' had about the size of related forms such as ''[[Glossotherium]]'' or ''[[Paramylodon]]'', but was significantly smaller than the giant ''[[Lestodon]]''. In terms of physique, it largely corresponded with the other large ground-living sloths.<ref name="Bell2002">{{cite journal |last1=Bell |first1=C. M. |title=Did elephants hang from trees? – the giant sloths of South America |journal=Geology Today |date=March 2002 |volume=18 |issue=2 |pages=63–66 |doi=10.1046/j.1365-2451.2002.00334.x |bibcode=2002GeolT..18...63B |s2cid=130426084 }}</ref><ref name="forasiepietal2007">{{cite book |last1=Forasiepi |first1=Analía |last2=Martinelli |first2=Agustín |last3=Blanco |first3=Jorge Luis |title=Bestiario fósil: mamíferos del pleistoceno de la Argentina |trans-title=Fossil bestiary: Pleistocene mammals of Argentina |language=es |date=2007 |publisher=Albatros |isbn=978-950-24-1101-9 |oclc=230208342 |pages=60–61 }}</ref>

=== Skull and dentition features ===
Especially in the construction of the skull, ''Mylodon'' differed significantly from other related forms. Its length varied between 59 and 71.5 cm, which is significantly longer than ''Glossotherium'' or ''Lestodon''. At the skull it was between 16.5 and 22.5 cm wide, in the front nasal area between 11.3 and 15.5 cm. The height of the posterior skull was 14.0 to 19.0 cm and the anterior 15.0 to 23.5 cm.<ref name="brandonietal2010">{{cite journal |last1=Brandoni |first1=Diego |last2=Ferrero |first2=Brenda S. |last3=Brunetto |first3=Ernesto |title=Mylodon darwini Owen (Xenarthra, Mylodontinae) from the Late Pleistocene of Mesopotamia, Argentina, with remarks on individual variability, paleobiology, paleobiogeography, and paleoenvironment |journal=Journal of Vertebrate Paleontology |date=September 2010 |volume=30 |issue=5 |pages=1547–1558 |doi=10.1080/02724634.2010.501449 |bibcode=2010JVPal..30.1547B |s2cid=86181187 |hdl=11336/79988 |hdl-access=free }}</ref> The skull was thereby elongated and narrow, unlike ''Glossotherium'' and ''Lestodon'' that had a short and very broad skull. The extraordinary length of the skull of ''Mylodon'' was mainly due to elongations in the [[rostrum (anatomy)|rostrum]]. Seen from above, the rostrum narrowed towards the front. This is where the most important difference to most of the other representatives of the Mylodontidae can be found: The nasal bone was long and narrow and curved downwards in the front area. At the front end, it connected to the middle jawbone, which was lengthened by an appendage, and which in turn fused with the upper jaw. This resulted in a completely closed nasal arch in adult individuals, which is largely unknown in other sloths. In comparison, the skulls of ''Glossotherium'' and ''Lestodon'', but also of ''Paramylodon'', showed a nasal area, seen from above, which was rather short and looked clearly cut off when viewed from the side; the roof of the skull was largely straight in ''Mylodon'', only a slight indentation could occur above the orbit. On parietal, significant temporal lines were present, but no head crest formed. The zygomatic arch was slim, the anterior attachment began above the third and fourth molars. It did not form a solid end with the rear arch attachment. As is usual with sloths, the front arch base consisted of three appendages: one ascending, one horizontal, and one descending, the former of which was the longest. The rear arch formed a triangular plate. The occiput bent at an angle of 120° from the roof of the skull. The underside of the occiput was at about the level of the occlusal plane. When viewed from behind, the occiput appeared almost circular and not as depressed as in ''Glossotherium'' and ''Lestodon''.<ref name="brambilla&ibarra2018">{{cite journal |last1=Brambilla |first1=Luciano |last2=Ibarra |first2=Damian A. |title=The occipital region of late Pleistocene Mylodontidae of Argentina |journal=Boletín del Instituto de Fisiografía y Geología |date=15 November 2018 |volume=88 |pages=1–9 |url=https://www.fceia.unr.edu.ar/fisiografia/volumen88/brambilla_etal_bifg88.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.fceia.unr.edu.ar/fisiografia/volumen88/brambilla_etal_bifg88.pdf |archive-date=2022-10-09 |url-status=live |hdl=2133/14367 |hdl-access=free }}</ref> The palate was narrow and was more or less triangularly oriented towards the front of the skull. Numerous small bone openings were characteristic here. The glenoid pit, in which the joint of the lower jaw engages, corresponding to that of other mylodonts with its weak form, but this provided free rotation overall.<ref name="brandonietal2010" /><ref name="bargo&vizcaino2008">{{cite journal |last1=Bargo |first1=M. Susana |last2=Vizcaíno |first2=Sergio F. |title=Paleobiology of Pleistocene ground sloths (Xenarthra, Tardigrada): biomechanics, morphogeometry and ecomorphology applied to the masticatory apparatus |journal=Ameghiniana |date=2008 |volume=45 |issue=1 |pages=175–196 |url=https://www.ameghiniana.org.ar/index.php/ameghiniana/article/view/216 }}</ref><ref name="mcafee2007">{{cite thesis |last1=McAfee |first1=R.K. |year=2007 |title=Reassessing the Taxonomy and Affinities of the Myodontinae sloths, ''Glossotherium'' and ''Paramylodon'' (Mammalia: Xenarthra: Tardigrada) }}</ref>

[[File:Mylodon jaw.jpg|thumb|right|Lower jaw of ''Mylodon'']]
The lower jaw of ''Mylodon'' varied in length between 42 and 48 cm. It was elongated, more noticeable than in ''Glossotherium'' and ''Lestodon'', since in ''Mylodon'' the area in front of the teeth, in particular, is strongly elongated. The horizontal bone body increased continuously in height towards the rear, below the last molar it was about 10.5 to 12.7 cm. The symphysis at the front end for the jointing of the two halves of the lower jaw was about 12.4 cm long. Here the lower edge of the body of the lower jaw rose at an angle so that the anterior end of the symphysis was above the occlusal plane of the teeth. As with other sloths, the symphysis extended forward, it ended slightly rounded. According to the rostrum of the skull, ''Mylodon'''s symphysis was narrow and not as wide as in ''Glossotherium'' and ''Lestodon''. The mandible foramen opened shortly behind the symphysis. The ascending branch started behind the last molar and formed an angle of 140° to the occlusal plane. The crown process rose up to 20&nbsp;cm. In contrast, the articular process was lower, roughly at the level of the occlusal plane, resulting in a low cranial-mandibular connection. The angular process at the rear end of the lower jaw was clearly visible. Sometimes it tipped down and was below the lower edge of the horizontal bone body. The upper side of the angular process does not reach the occlusal plane.<ref name="brandonietal2010" /><ref name="bargo&vizcaino2008" /><ref name="mcafee2007" />

The dentition of ''Mylodon'' differs greatly from that of the other [[placental|placental mammals]] and usually consists of five teeth at the top and four teeth at the bottom per jaw arch, meaning a total of 18 teeth. In the mylodonts, the first tooth was often [[canine (tooth)|caniniform]] while the rear teeth were more [[molar (tooth)|molariform]]. Within the sloth, this structure of the teeth can be called original. A special feature of ''Mylodon'' was that the upper canine-like tooth of each row was completely regressed and only the molar-like four rear teeth were found here. In the lower row of teeth, the anterior caniniform tooth was transformed into a molariform. The dentition thus consisted of a total of 16 teeth. This is somewhat reminiscent of ''Paramylodon'', in which the upper canine-shaped teeth were also missing, but the lower ones had retained their strikingly pointed shape. In contrast to this, ''Glossotherium'' and ''Lestodon'' had the original decayed teeth. The flat, flap-like and largely indented structure of the '' molariform '' teeth can be emphasized as a characteristic of the mylodonts, which clearly differs from that of the [[Megatheriidae]] and [[Megalonychidae]] with their two transverse raised ridges per tooth. The shapes of the teeth present in ''Mylodon'' were simpler. In the upper jaw row, they had a rather round to oval outline, in the lower jaw row a more [[diamond]]-shaped outline. The typically more complex bilobed design of the molar-like teeth of ''Glossotherium'' and ''Lestodon'', caused by a central constriction, only occurred on the lower rearmost tooth in ''Mylodon''. In general, the rows of teeth diverged to the front, and the teeth were very high crowned ([[hypsodont]]). The upper row of teeth ranges in length from 10.9 to 13.3&nbsp;cm, the lower row was between 12.0 and 15.0&nbsp;cm in length.<ref name="bargo&vizcaino2008" /><ref name="brandonietal2010" /><ref name="mcafee2007" /><ref name="bargoetal2006">{{cite journal |last1=Bargo |first1=M. Susan |last2=De Iuliis |first2=Gerardo |last3=Vizcaíno |first3=Sergio F. |title=Hypsodonty in Pleistocene ground sloths |journal=Acta Palaeontologica Polonica |date=2006 |volume=51 |issue=1 |pages=53–61 |url=http://webaccess.app.pan.pl/article/item/app51-053.html |citeseerx=10.1.1.728.7025 }}</ref>

=== Postcrania ===
Postcranial skeletons are far rarer in ''Mylodon'' than in the other large mylodontid sloths. As a result, the skeleton is less well documented. Only individual elements of the spine, such as the atlas and various thoracic vertebrae, have been described. The humerus was massive and extremely long at 46 to 48&nbsp;cm. The joint head, the diameter of which was over 10&nbsp;cm, stood out due to its hemispherical, but laterally somewhat flattened shape. A distinct deltopectoral ridge ran down the shaft, which acted as an anchor point for the shoulder muscles. As with many ground sloths, the lower end of the joint extended far and brought it here to a width of almost 26&nbsp;cm. In part, this was caused by a massive internal epicondyle. The articular surfaces (capitulum and trochlea) were almost perpendicular to each other and did not form such an obtuse angle as in ''Glossotherium''. The cubit was built gracefully. Their length was around 37&nbsp;cm. The olecranon, i.e. the upper articular process, took up about 8.1&nbsp;cm of it, which corresponds to about 22% of the total length and is significantly less than in comparison with ''Glossotherium'' and ''Lestodon''. It was laterally narrowed, which is also found in ''Paramylodon''. The spoke largely resembled that of Glossotherium and was compact and straight built with a length of about 30&nbsp;cm. The head was oval in shape with a prominent lip. The pelvis was extremely expansive and 114&nbsp;cm wide between the two iliac bones. The thigh bone measured between 55 and 59&nbsp;cm in length. It was typical of ground sloths, being flat in shape. Its width decreased significantly on the shaft, the lowest value was reached just below the midpoint. Here the width was about 18&nbsp;cm, the thickness about 7.5&nbsp;cm. The joint ends, on the other hand, were markedly wider, around 30&nbsp;cm at the knee end and around 26&nbsp;cm at the foot end. The thighbone reached the shin with only about half of its length, a characteristic of mylodonts. This bone, too, was clearly flat with a thickness that was only half the value of the width at the shaft. The fibula is so far only fragmented. It was drawn in on the shaft and widened at the joint ends, with the upper joint end showing more pronounced curves than in ''Glossotherium''.<ref name="kraglievich1934">Lucas Kraglievich: Contribución al conocimiento de ''Mylodon darwini'' Owen y especies afines. Revista del Museo de La Plata 34, 1934, pp. 255–292</ref><ref name="mcafee2016">{{cite journal |last1=McAfee |first1=Robert K. |title=Description of New Postcranial Elements of Mylodon darwinii Owen 1839 (Mammalia: Pilosa: Mylodontinae), and Functional Morphology of the Forelimb |journal=Ameghiniana |date=August 2016 |volume=53 |issue=4 |pages=418–443 |doi=10.5710/AMGH.24.02.2016.2950 |s2cid=88450788 }}</ref><ref name="haroetal2017">{{cite journal |last1=Haro |first1=José A. |last2=Tauber |first2=Adan A. |last3=Krapovickas |first3=Jerónimo M. |title=Thoracic member (pectoral girdle and forelimb) bones of Mylodon darwinii Owen (Xenarthra, Mylodontidae) from the Late Pleistocene of Central Argentina and their phylogenetic implications |journal=PalZ |date=September 2017 |volume=91 |issue=3 |pages=439–457 |doi=10.1007/s12542-017-0350-z |bibcode=2017PalZ...91..439H |s2cid=90593541 }}</ref>

The hand comprised a total of five digits (I to V), whereby the metacarpal bone was fused with the large polygonal bone on the first digit. This created the so-called Metacrapal Carpal Complex (MCC for short), which is typical for many ground sloths. As a special feature of the wrist, the pea bone was clearly flat, its shape resembled that of ''Glossotherium'', but differed from the corresponding bone of other Mylodonts with spherical, walnut-like or a pyramidal shape. The fourth digit had formed the longest metacarpal bone, while that of the fifth was only slightly shorter. The respective bones measured there around 12.5 and 10.7&nbsp;cm in length. As with ''Glossotherium'' and ''Paramylodon'', only the three inner digits were probably clawed, but only of the second digit have all bone elements been documented. The metacarpal bone was 7.8&nbsp;cm long and was built very gracefully. The first phalanx was extremely short and only about 2.5&nbsp;cm long, the second was about 4.2&nbsp;cm long and the third at least 11.5&nbsp;cm. It was tubular and went forward into an extension on which the claw rested. The first phalanges of the two outer digits were significantly reduced in length. Only individual root bones of the foot, such as the talus, are present.<ref name="mcafee2016" />

=== Integument ===
[[File:Mylodon darwini - skin, droppings and toenails.JPG|thumb|Toenails, dung and skin, Natural History Museum, London]]
[[File:Mylodon fur.jpg|thumb|Fur and skin at the Museum für Naturkunde, Berlin]]
''Mylodon'' is one of the few extinct mammals that has mummified skin remains. The most important location for such finds is the Cueva del Milodón in the Chilean province of Última Esperanza, where the first skin parts were brought to light at the end of the 19th century.<ref name="moreno&woodward1899"/><ref name="nordenskjöld1899">Otto Nordenskjöld (with the participation of other authors): Scientific results of the Swedish expedition to the Magellan lands 1895–1897, under the direction of Dr. Otto Nordenskjöld. Volume II: Zoology. Stockholm, 1899, pp. 1–170 (especially pp. 149–170)</ref> Individual pieces have lengths of up to 150&nbsp;cm, but have shrunk through drying processes. Its thickness is up to 1.5&nbsp;cm in some places, but it is usually around 1&nbsp;cm. The skin is densely covered with stiff, slightly wavy hair, with only the top hair being developed, while the undercoat is missing. This feature is similar to the [[Choloepus|two-toed sloths]] but less so than the [[Bradypus|three-toed sloths]], which possess an undercoat. The length of the individual hairs vary between 5 and sometimes over 20&nbsp;cm with the shortest in the area of the back of the head, medium-length hair on the back and very long hair on the limbs. Their known color ranges from yellowish to reddish-brown. The hair shafts are uniformly tubular, at the upper end they form blunt tips. As with today's sloths, the hair did not have a pith (medulla). In contrast to the hair of the two-toed sloth, they lack their characteristic longitudinal ribbing.<ref name="moreno&woodward1899">{{cite journal |first1=Francesco P. |last1=Moreno |first2=Arthur Smith |last2=Woodward |title=On a Portion of Mammalian Skin, named ''Neomylodon listai'', from a Cave near Consuelo Cove, Last Hope Inlet, Patagonia |journal=Proceedings of the Zoological Society |year=1899 |pages=144–156 }}</ref><ref name="nordenskjöld1899"/><ref name="lonnberg1900">{{cite journal |first1=Einar |last1=Lönnberg |title=On a remarkable piece of skin from Cueva Eberhardt, Last Hope Inlet, Patagonia |journal=Proceedings of the Zoological Society |volume=199 |year=1900 |pages=379–383 }}</ref><ref name="woodward1900">{{cite journal |last1=Woodward |first1=A. Smith |title=On some Remains of Grypotherium (Neomylodori) listai and associated Mammals from a Cavern near Consuelo Cove, Last Hope Inlet, Patagonia. |journal=Proceedings of the Zoological Society of London |date=21 August 2009 |volume=69 |issue=1 |pages=64–78 |doi=10.1111/j.1096-3642.1890.tb01704.x |url=https://www.biodiversitylibrary.org/part/72554 }}</ref><ref name="ridewood1901">{{cite journal |last1=Ridewood |first1=W. G. |title=Memoirs: On the Structure of the Hairs of Mylodon Listai and other South American Edentata |journal=Journal of Cell Science |date=1 May 1901 |volume=s2-44 |issue=175 |pages=393–411 |doi=10.1242/jcs.s2-44.175.393 |doi-access=free }}</ref>

The mylodonts are the only representatives of the sloths to have bony plates embedded in their skin. Such structures, called [[osteoderms]], are known today to a greater extent only in armadillos. In contrast to the outer armor of the armadillos, the bone platelets of the mylodonts were rather loosely scattered. Hermann Burmeister published the first finds of individual osteoderms of ''Mylodon'' as early as the 1860s.<ref name="burmeister1865">Hermann Burmeister: skin armor at Mylodon. Archives for anatomy, physiology and scientific medicine 1865, pp. 334–336</ref><ref name="burmeister1867">Hermann Burmeister: Fauna Argentina. Primera party. Mamiferos fósiles. Lista de los mamiferos fósiles del terreno diluviano. Anales del Museo Público de Buenos Aires 1, 1867, pp. 87–300 (p. 173)</ref> The remains of skin found in the caves of Última Esperanza give an impression of how they were embedded in the skin and distributed over the body. The bone platelets are all located in the lower section of the skin, while the hairs originate in the upper sections. The distribution turned out to be very inconsistent. Some areas with a dense array of osteoderms contain between 83 and 95 platelets per 10&nbsp;cm<sup>2</sup>. For others, however, the number is very thin. However, even with a close arrangement, the osteoderms never unite to form a closed shell, but are always separated from one another by individual skin folds. In accordance with the armadillos' shells, the bone platelets form a single layer and do not appear stacked. Since all skin residues were found isolated from the body skeletons, it is sometimes difficult to assign the skin areas with a dense and thin arrangement of bone platelets to a specific part of the body. However, it can be assumed that the back was largely armored and the stomach was free. In the sections with dense osteoderm formation, these were larger than in the clear areas. The bone platelets of ''Mylodon'' were mostly of irregular oval shape with dimensions of 0.5 to 2.5&nbsp;cm in length, 0.3 to 1.8&nbsp;cm in width and 0.2 to 1.1&nbsp;cm in thickness, with weights of a maximum of 2&nbsp;g. On the surface, they showed individual dimples.<ref name="hill2005">{{cite journal |last1=Hill |first1=Robert V. |title=Comparative anatomy and histology of xenarthran osteoderms |journal=Journal of Morphology |date=December 2006 |volume=267 |issue=12 |pages=1441–1460 |doi=10.1002/jmor.10490 |pmid=17103396 |s2cid=22294139 }}</ref> In cross-section, they consisted of numerous bundles of fibers mixed with hard bone blades (osteoma). This made their structure much simpler than that of the armadillos, and they probably lacked the keratin layer known from the armadillos. In principle, the osteoderms of ''Mylodon'' were similar to those of other large mylodonts.<ref name="moreno&woodward1899"/><ref name="nordenskjöld1899"/><ref name="lopezmendozaetal2011">{{cite journal |last1=López-Mendoza |first1=Patricio |last2=Mena-Larraín |first2=Francisco |title=Extinct ground sloth dermal bones and their role in the taphonomic research of caves: the case of Baño Nuevo-1 (Andean Central Patagonia, Chile) |journal=Revista Mexicana de Ciencias Geológicas |date=December 2011 |volume=28 |issue=3 |pages=519–532 |url=http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1026-87742011000300013 }}</ref><ref name="branco1906">Wilhelm Branco: The application of X-rays in paleontology. Treatises of the Royal Prussian Academy of Sciences Berlin 1906, pp. 1–55</ref><ref name="hill2005"/><ref name="mcdonald2018">{{cite journal |last1=McDonald |first1=H. Gregory |title=An Overview of the Presence of Osteoderms in Sloths: Implications for Osteoderms as a Plesiomorphic Character of the Xenarthra |journal=Journal of Mammalian Evolution |date=December 2018 |volume=25 |issue=4 |pages=485–493 |doi=10.1007/s10914-017-9415-8 |s2cid=38600428 }}</ref>

==Distribution and important fossil finds==
===Overview and origins===
''Mylodon'' was mainly distributed in the southern part of South America. Fossil finds are known from Argentina, Chile, southern Bolivia, Uruguay, Paraguay and southern Brazil.<ref>{{Cite journal |last1=Brandoni |first1=Diego |last2=Ferrero |first2=Brenda S. |last3=Brunetto |first3=Ernesto |date=September 2010 |title=Mylodon darwini Owen (Xenarthra, Mylodontinae) from the Late Pleistocene of Mesopotamia, Argentina, with remarks on individual variability, paleobiology, paleobiogeography, and paleoenvironment |url=https://www.tandfonline.com/doi/full/10.1080/02724634.2010.501449 |journal=Journal of Vertebrate Paleontology |language=en |volume=30 |issue=5 |pages=1547–1558 |doi=10.1080/02724634.2010.501449 |bibcode=2010JVPal..30.1547B |hdl=11336/79988 |issn=0272-4634|hdl-access=free }}</ref> Thus, the colonized regions include very far southern sites on the island of [[Tierra del Fuego]] as well as most of [[Patagonia]] northward to the [[Pampas]] region. Its northern limit was around 19.6° S, while its southern limit reached the range at about 53° south. The Tres Arroyos site on Tierra del Fuego and the region around Cueva del Milodón in southwestern Patagonia are among the southernmost known records of a sloth representative in the Pleistocene.<ref>{{Cite journal |last=McDonald |first=H. Gregory |date=June 2023 |title=A Tale of Two Continents (and a Few Islands): Ecology and Distribution of Late Pleistocene Sloths |journal=Land |language=en |volume=12 |issue=6 |pages=1192 |doi=10.3390/land12061192 |doi-access=free |issn=2073-445X}}</ref><ref name="latorre1998">Claudio Latorre: "Paleontología de mamíferos del alero Tres Arroyos 1, Tierra del Fuego". In: ''Anales del Instituto de la Patagonia''. Volume 26, 1998, pp. 77–90.</ref><ref name="mcdonald2008">H. Gregory McDonald, Gerardo de Iuliis: "Fossil history of sloths". In: Sergio F. Vizcaíno, WJ Loughry (Ed.): ''The Biology of the Xenarthra''. University Press of Florida, 2008, pp. 39–55.</ref> In the Pampa region, the northern limit was found approximately at the Chuí River in the southeastern Brazilian state of Rio Grande do Sul around 30 degrees south latitude. Even more northerly points of discovery, such as Ñuapua in Bolivia, are tangent to the 20th parallel south. Finds reported from Paraguay, however, are considered rather uncertain.<ref name="marshalletal1984">{{cite journal |last1=Marshall |first1=Larry G. |last2=Berta |first2=Annalisa |last3=Hoffster |first3=Robert |last4=Pascual |first4=Rosendo |last5=Reig |first5=Osvaldo A. |last6=Bombin |first6=Miguel |last7=Mones |first7=Alvaro |title=Mammals and stratigraphy: geochronology of the continental mammal-bearing quaternary of South America |journal=Palaeovertebrata |date=1983 |pages=1–76 |url=http://cuevasdelperu.org/publicaciones/peru/1984_Paleovertebra_Marshall.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://cuevasdelperu.org/publicaciones/peru/1984_Paleovertebra_Marshall.pdf |archive-date=2022-10-09 |url-status=live }}</ref><ref name="marshall&sempere1991">{{cite book |first1=Larry G. |last1=Marshall |first2=Thierry |last2=Sempere |chapter=The Eocene to Pleistocene vertebrates of Bolivia and their stratigraphic context: a review |pages=631–652 |chapter-url=https://horizon.documentation.ird.fr/exl-doc/pleins_textes/pleins_textes_7/b_fdi_57-58/010024180.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://horizon.documentation.ird.fr/exl-doc/pleins_textes/pleins_textes_7/b_fdi_57-58/010024180.pdf |archive-date=2022-10-09 |url-status=live |editor1-last=Suárez Soruco |editor1-first=Ramiro |title=Fósiles y facies de Bolivia. Vol. 1, Vertebrados Vol. 1, Vertebrados |date=1991 |series=Revista Técnica de Yacimientos Petrolíferos Fiscales Bolivianos |volume=12 |issue=3–4 |oclc=954042711 }}</ref><ref name="favottietal2015">{{cite journal |last1=Favotti |first1=Sergio Emmanuel |last2=Ferrero |first2=Brenda Soledad |last3=Brandoni |first3=Diego |title=Primer registro de Mylodon Darwini Owen (xenarthra, tardigrada, mylodontidae) en la formación Arroyo Feliciano (pleistoceno tardío), Entre Ríos, Argentina |journal=Revista Brasileira de Paleontologia |date=December 2015 |volume=18 |issue=3 |pages=547–554 |doi=10.4072/rbp.2015.3.15 |doi-access=free |hdl=11336/42066 |hdl-access=free }}</ref>

The first occurrence of ''Mylodon'' may have been in the Lower Pleistocene, but finds are rather rare.<ref name="scillatoyaneetal1995">{{cite book |first1=Gustavo J. |last1=Scillato-Yané |first2=Alfredo A. |last2=Carlini |first3=Sergio F. |last3=Vizcaíno |first4=Edgardo Ortiz |last4=Jaureguizar |chapter=Los Xenartros |pages=183–175 |editor1-last=Alberdi |editor1-first=M. T. |editor2-last=Leone |editor2-first=Gabriello |editor3-last=Tonni |editor3-first=Eduardo P. |title=Evolución biológica y climática de la región pampeana durante los últimos cinco millones de años: un ensayo de correlación con el Mediterráneo Occidental |date=1995 |publisher=Museo Nacional de Ciencias Naturales |isbn=978-84-00-07558-3 |language=es}}</ref><ref name="carlinietal1999">{{cite book |first1=Alfredo A. |last1=Carlini |first2=Gustavo J. |last2=Scillato-Yané |chapter=Evolution of Quaternary Xenarthrans (Mammalia) of Argentina |editor1-first=Jorge |editor1-last=Rabassa |editor2-first=Mónica |editor2-last=Salemme |title=Quaternary of South America and Antarctic Peninsula |location=Rotterdam |year=1999 |pages=149–175 }}</ref> During this period, the possibly closely related form ''[[Archaeomylodon]]'' also occurred in the Pampas region, whose foremost canine teeth of the upper dentition were greatly reduced in size, but not yet completely reduced.<ref name="brambillaetal2018">{{cite journal |last1=Brambilla |first1=Luciano |last2=Ibarra |first2=Damián Alberto |title=Archaeomylodon sampedrinensis , gen. et sp. nov., a new mylodontine from the middle Pleistocene of Pampean Region, Argentina |journal=Journal of Vertebrate Paleontology |date=2 November 2018 |volume=38 |issue=6 |pages=e1542308 |doi=10.1080/02724634.2018.1542308 |bibcode=2018JVPal..38E2308B |s2cid=91874640 }}</ref> Among the early and more northerly finds of ''Mylodon'' is, for example, a skull from the El Palmar Formation in the Argentine province of Entre Ríos, which dates to the end of the last warm period about 80,000 years ago.<ref name="brandonietal2010"/> Also from the northern distribution areas two partial skeletons are worth mentioning, one of which was found at the Río Anisacate in the Argentine province of Córdoba and the other in Arroyo Quequén Salado near Oriente in the Argentine province of Buenos Aires. Mainly in the Pampas, there was an overlap in the occurrence of ''Mylodon'' with the two other major mylodontid sloth representatives ''[[Glossotherium]]'' and ''[[Lestodon]]'' during the Upper Pleistocene. However, actual co-occurrence is rarely attested. These include the important archaeological site of Paso Otero in Buenos Aires Province, the locality of Arroyo de Vizcaíno in southern Uruguay, and the Chuí River.<ref name="farinaetal2014">{{cite journal |last1=Fariña |first1=Richard A. |last2=Tambusso |first2=P. Sebastián |last3=Varela |first3=Luciano |last4=Czerwonogora |first4=Ada |last5=Di Giacomo |first5=Mariana |last6=Musso |first6=Marcos |last7=Bracco |first7=Roberto |last8=Gascue |first8=Andrés |title=Arroyo del Vizcaíno, Uruguay: a fossil-rich 30-ka-old megafaunal locality with cut-marked bones |journal=Proceedings of the Royal Society B: Biological Sciences |date=7 January 2014 |volume=281 |issue=1774 |pages=20132211 |doi=10.1098/rspb.2013.2211 |pmid=24258717 |pmc=3843831 }}</ref>

===Important Upper Pleistocene finds===
As with many of the other large ground sloths, most of the ''Mylodon'' material is from the Upper Pleistocene, with a focus toward the end of the last glacial period. It is also the phase when ''Mylodon'' again disappeared from the fossil record. From a global perspective, numerous larger animals became extinct during the transition from the Pleistocene to the Holocene, which is why this event is considered a Quaternary extinction wave. In South America, this coincides with the first appearance of humans. Whether the two are causally related is the subject of much controversy. In addition to potential hunting and possible landscape overprinting by early human hunter-gatherer groups, climatic changes may also have had an influence.<ref name="villavincencioetal2016">{{cite journal |last1=Villavicencio |first1=Natalia A. |last2=Lindsey |first2=Emily L. |last3=Martin |first3=Fabiana M. |last4=Borrero |first4=Luis A. |last5=Moreno |first5=Patricio I. |last6=Marshall |first6=Charles R. |last7=Barnosky |first7=Anthony D. |title=Combination of humans, climate, and vegetation change triggered Late Quaternary megafauna extinction in the Última Esperanza region, southern Patagonia, Chile |journal=Ecography |date=February 2016 |volume=39 |issue=2 |pages=125–140 |doi=10.1111/ecog.01606 |doi-access=free |bibcode=2016Ecogr..39..125V }}</ref> Numerous archaeological sites, especially in the Pampa region and in the Patagonian area, are between 13,500 and 10,000 years old. The majority of these attest to at least a coexistence of humans and ground sloths over an extended period of time. Direct associations of human cultural products and fossil remains of ''Mylodon'' are found, among others, at [[Gruta del Indio]] in the eastern foothills of the Andes, at Piedra Museo or Las Buitreras, all in Argentina, and at Tres Arroyos in Tierra del Fuego, respectively.

''Mylodon'' is often represented by isolated osteoderms, bones or in the form of coprolites, while human remains are limited to stone artifacts and/or hearths. Whether this also involved a more or less intensive raw material use of sloth bones on the part of humans is in many cases unproven. Numerous bone marks that were originally interpreted as anthropogenically caused are, according to recent studies, due to predation. Evidence of direct hunting by humans of the large ground sloths is even more difficult. One piece of evidence is often considered to be Quebrada de Quereo, a site on an ancient coastline in northern Chile. From here come, among other things, skeletal remains of two individuals of ''Mylodon'', distributed in each case over a narrowly defined area, but in two different stratigraphic units and at a spatial distance of 21 m from each other. One of the individuals was associated with about 70 stone objects, whose anthropogenic origin is under discussion. No cut marks are found on the bones as evidence of any human manipulation. The age of the site is given as 11,600 to 10,900 years before present.<ref name="jacksonetal2003">Donald Jackson S .: "Evaluating evidence of cultural associations of Mylodon in the semiarid region of Chile". In: L. Miotti, M. Salemme, M. Flegenheimer (Eds.): ''Where the south winds blow: ancient evidence of Paleo South Americans''. Texas A&M University, 2003, pp. 77–81.</ref><ref name=Borrero2009>{{cite book |doi=10.1007/978-1-4020-8793-6_8 |chapter=The Elusive Evidence: The Archeological Record of the South American Extinct Megafauna |title=American Megafaunal Extinctions at the End of the Pleistocene |series=Vertebrate Paleobiology and Paleoanthropology |year=2009 |last1=Borrero |first1=Luis Alberto |pages=145–168 |isbn=978-1-4020-8792-9 }}</ref>

[[File:Milodon cave.JPG|thumb|left|Entrance of [[Cueva del Milodón]]]]
[[File:Knochen milodon cueva del milodon 2018-11-14.jpg|thumb|Various finds of ''Mylodon'' from Cueva del Milodón (femur, mandible, hair)]]
One of the most important sites is the Cueva del Milodón near [[Lago Sofía]] in the Chilean province of [[Última Esperanza Province|Última Esperanza]], known mainly for its surviving skin remains. It is part of a whole system of caves in the region, such as the [[Cueva del Medio]]<ref name="Martin et al. 2015">{{cite journal |last1=Martin |first1=Fabiana M |last2=Todisco |first2=Dominique |last3=Rodet |first3=Joël |last4=San Román |first4=Manuel |last5=Morello |first5=Flavia |last6=Prevosti |first6=Francisco |last7=Stern |first7=Charles |last8=Borrero |first8=Luis A |title=Nuevas excavaciones en Cueva del Medio: Procesos de formación de la cueva y avances en los estudios de interacción entre cazadores-recolectores y fauna extinta (Pleistoceno Final, Patagonia Meridional) |trans-title=New excavations in Cueva del Medio: Cave formation processes and advances in the interaction studies between hunter-gatherers and extinct fauna (Late Pleistocene, Southern Patagonia) |language=es |journal=Magallania (Punta Arenas) |date=2015 |volume=43 |issue=1 |pages=165–189 |doi=10.4067/S0718-22442015000100010 |doi-access=free |hdl=11336/46105 |hdl-access=free }}</ref><ref name="Nami et al. 2015">Hugo G. Nami, Calvin J. Heusser: Cueva del Medio: A Paleoindian Site and Its Environmental Setting in Southern South America. In: Archaeological Discovery. Volume 3, 2015, pp. 62–71.</ref> or the [[Cueva Chica]],<ref name="Martin et al. 2013">{{cite journal |last1=Martin |first1=Fabiana |last2=San Román |first2=Manuel |last3=Morello |first3=Flavia |last4=Todisco |first4=Dominique |last5=Prevosti |first5=Francisco J. |last6=Borrero |first6=Luis A. |title=Land of the ground sloths: Recent research at Cueva Chica, Ultima Esperanza, Chile |journal=Quaternary International |date=August 2013 |volume=305 |pages=56–66 |doi=10.1016/j.quaint.2012.11.003 |bibcode=2013QuInt.305...56M |hdl=11336/3082 |hdl-access=free }}</ref> which line the southern flank of the 556 m high [[Cerro Benitez]] like pearls. Cueva del Milodón is a large cave 250&nbsp;m long, 140&nbsp;m wide and 30&nbsp;m high at the entrance and 10&nbsp;m at the back, respectively. It was discovered in 1895 by the German captain [[Hermann Eberhard]], who also found the first skin remains. The great importance of these finds led to the cave, initially known as "Cueva Eberhardt", being subsequently visited and explored by numerous scientists. As a result, a large number of finds accumulated over time, among which ''Mylodon'' with bone remains, and numerous [[coprolite]]s has a large share. Other finds belong to [[camels]] such as ''[[Lama (genus)|Lama]]'', [[Equidae|horses]] such as ''[[Hippidion]]'' or [[South American ungulates]] such as ''[[Macrauchenia]]'', in addition, several [[predators]] are represented, including the [[jaguar]], ''[[Smilodon]]'' as a member of the [[saber-toothed cats]], and the giant [[bear]] form ''[[Arctotherium]]''. Some of the mammal bones have marks that were originally associated with human activity, but the current view is that they are more likely due to predator browsing. In addition to faunal remains, the cave also held a myriad of botanical material. It also yielded one of the most extensive data sequences from the Upper Pleistocene. Several [[radiocarbon dating|radiocarbon dates]], measured from a wide variety of ''Mylodon'' finds, span a period from about 16,700 to 10,200 years ago. The upper data are among the most recent obtained directly from finds of the sloth vertebrate.<ref name="Tonni et al. 2003">{{cite journal |last1=Tonni |first1=Eduardo P. |last2=Carlini |first2=Alfredo A. |last3=Yané |first3=Gustavo J. Scillato |last4=Figini |first4=Aníbal J. |title=Cronología radiocarbónica y condiciones climáticas en la 'Cueva del Milodón' (sur de Chile) durante el Pleistoceno Tardío |journal=Ameghiniana |trans-title=Radiocarbon chronology and climatic conditions in the 'Cueva del Milodon' (southern Chile) during the Late Pleistocene |language=es |date=2003 |volume=40 |issue=4 |pages=609–615 |url=https://www.ameghiniana.org.ar/index.php/ameghiniana/article/view/987 }}</ref><ref name=Borrero2009/><ref name="Barnosky et al. 2010">{{cite journal |last1=Barnosky |first1=Anthony D. |last2=Lindsey |first2=Emily L. |title=Timing of Quaternary megafaunal extinction in South America in relation to human arrival and climate change |journal=Quaternary International |date=April 2010 |volume=217 |issue=1–2 |pages=10–29 |doi=10.1016/j.quaint.2009.11.017 |bibcode=2010QuInt.217...10B }}</ref><ref name="Borrero & Martin 2012"/><ref name="Borrero et al. 2012b">{{cite journal |last1=Borrero |first1=Luis Alberto |last2=Martin |first2=Fabiana María |title=Ground sloths and humans in southern Fuego-Patagonia: taphonomy and archaeology |journal=World Archaeology |date=March 2012 |volume=44 |issue=1 |pages=102–117 |doi=10.1080/00438243.2012.646145 |s2cid=86180858 }}</ref>

== Taxonomy ==
''Mylodon'''s close relatives include the ground sloths of the genera ''Glossotherium'' and ''Paramylodon''. The latter genus has often been confused with ''Glossotherium'', but ''Paramylodon'' is a distinct genus that was restricted to the [[Pleistocene]] of North America.<ref name="mcafee2007"/> ''Glossotherium'' also shares a long history of taxonomic confusion with ''Mylodon'', and currently the only recognized species is ''Mylodon darwini''. At one time, the elephant-sized ''[[Megatherium]]'' was thought to be closely related, but is recognized as belonging to a separate family ([[Megatheriidae]]).

Below is a phylogenetic tree of the Mylodontidae, based on the work of Boscaini ''et al.''. 2019.<ref name="boscainietal2019">{{cite journal |last1=Boscaini |first1=Alberto |last2=Pujos |first2=François |last3=Gaudin |first3=Timothy J. |title=A reappraisal of the phylogeny of Mylodontidae (Mammalia, Xenarthra) and the divergence of mylodontine and lestodontine sloths |journal=Zoologica Scripta |date=November 2019 |volume=48 |issue=6 |pages=691–710 |doi=10.1111/zsc.12376 |s2cid=201194980 }}</ref>

{{clade|style=white-space:nowrap;font-size:100%;line-height:100%
|label1=[[Mylodontidae]]
|1={{clade
   |1={{clade
      |1=''[[Urumacotherium]]''
      |2=''[[Pseudoprepotherium]]''
      }}
   |2={{clade
      |1={{clade
         |1=''[[Paroctodontotherium]]''
         |2=''[[Octodontotherium]]''
         }}
      |2={{clade
         |1=''[[Brievabradys]]''
         |label2=[[Mylodontinae]]
          |2={{clade
            |label1=[[Lestodontini]]
            |1={{clade
               |1={{clade
                  |1=''[[Lestodon]]''
                  |2=''[[Bolivartherium]]''
                  }}
               |2={{clade
                  |1=''[[Thinobadistes]]''
                  |2={{clade
                     |1=''[[Sphenotherus]]''
                     |2=''[[Lestobradys]]''
                     }}
                  }}
               }}
            |label2=[[Mylodontini]]
            |2={{clade
               |1=''[[Pleurolestodon]]''
               |2={{clade
                  |1={{clade
                     |1=''[[Glossotheridium]]''
                     |2=''[[Simomylodon]]''
                     }}
                  |2={{clade
                     |1={{clade
                        |1={{clade
                           |1=''[[Kiyumylodon]]''
                           |2='''''Mylodon'''''
                           }}
                        |2=''[[Paramylodon]]''
                        }}
                     |2=''[[Glossotherium]]''
                     }}
                  }}
               }}
            }}
         }}
      }}
   }}
}}
Recent molecular sequence results obtained using [[collagen]]<ref name="Presslee2019">{{cite journal|last1= Presslee|first1= S.|last2= Slater|first2=G. J.|last3= Pujos|first3= F.|last4= Forasiepi|first4=A. M.|last5= Fischer|first5= R.|last6= Molloy|first6= K.|last7= Mackie|first7= M.|last8= Olsen|first8=J. V.|last9= Kramarz|first9= A.|last10= Taglioretti|first10= M.|last11= Scaglia|first11= F.|last12= Lezcano|first12= M.|last13= Lanata|first13=J. L.|last14= Southon|first14= J.|last15= Feranec|first15= R.|last16= Bloch|first16= J.|last17= Hajduk|first17= A.|last18= Martin|first18=F. M.|last19= Gismondi|first19= R. S.|last20= Reguero|first20 =M.|last21=de Muizon|first21= C.|last22= Greenwood|first22= A.|last23= Chait|first23=B. T.|last24= Penkman|first24= K.|author24-link= Kirsty Penkman |last25= Collins|first25= M.|last26= MacPhee|first26= R.D.E.|title= Palaeoproteomics resolves sloth relationships|journal=Nature Ecology & Evolution|volume= 3|issue= 7|pages= 1121–1130|year= 2019|doi= 10.1038/s41559-019-0909-z|pmid= 31171860|bibcode= 2019NatEE...3.1121P|s2cid= 174813630|url= https://eprints.whiterose.ac.uk/147061/1/5426_3_merged_1554730549.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://eprints.whiterose.ac.uk/147061/1/5426_3_merged_1554730549.pdf |archive-date=2022-10-09 |url-status=live}}</ref> and [[mitochondrial]] DNA<ref name="Delsuc2019">{{cite journal|last1= Delsuc|first1= F.|last2= Kuch|first2= M.|last3= Gibb|first3=G. C.|last4= Karpinski|first4= E.|last5= Hackenberger|first5= D.|last6= Szpak|first6= P.|last7= Martínez|first7=J. G.|last8= Mead|first8=J. I.|last9= McDonald|first9=H. G.|last10= MacPhee|first10= R.D.E.|last11= Billet|first11= G.|last12= Hautier|first12= L.|last13= Poinar|first13=H. N.|title= Ancient Mitogenomes Reveal the Evolutionary History and Biogeography of Sloths|journal= Current Biology|volume= 29|issue= 12|pages= 2031–2042.e6|year= 2019|doi= 10.1016/j.cub.2019.05.043|pmid= 31178321|url= https://www.researchgate.net/publication/333647272|doi-access= free|bibcode= 2019CBio...29E2031D|hdl= 11336/136908|hdl-access= free}}</ref> extracted from fossils indicate that the closest living relatives of ''Mylodon'' are the two-toed sloths of genus ''[[Choloepus]]''. This revelation came as a surprise, since morphological analyses had previously suggested that two-toed sloths were close to [[Caribbean sloth]]s and ''[[Megalonyx]]'', now regarded as representing two separate and distant branches of the sloth evolutionary tree.

Some authors suggest that there were two species, with ''M. darwini'' restricted to the Pampas, with the Patagonian remains belonging to the separate species ''Mylodon listai.''<ref name=":0" />

== History of research ==
=== First description ===
[[File:Richard Owen 1856.jpg|thumb|upright|left|[[Richard Owen]] (1856)]]
[[File:Mylodon holotype Owen 1840.png|thumb|left|The holotype of ''Mylodon'' used by Owen in his initial description]]
The taxonomic history of ''Mylodon'' is complex. It has involved confusion and equivocation with other mylodont forms such as ''[[Glossotherium]]'' and ''[[Paramylodon]]'' over a long period of time. Some of this complexity can be attributed to the [[first description|first describer]] of the genus itself, who is [[Richard Owen]] (1804-1892). Owen, one of the most important explorers of the Victorian era, was concerned from 1836 with fossil finds brought back by [[Charles Darwin]] from his pioneering voyage on [[HMS Beagle (1820)|HMS ''Beagle'']] to [[South America]]. The collection also included a mandible from [[Punta Alta]] near [[Bahía Blanca]] in the south of the [[Argentina]] [[Buenos Aires|Buenos Aires Province]] (specimen number [[Natural History Museum, London|NHM]] 16617). The nearly complete specimen was distinguished by a row of teeth consisting of a total of four [[molar (tooth)|molar-like]] Teeth. In an extensive 1840 paper, Owen referred the mandible to the new genus he had created, ''Mylodon,'' and named the species ''M. darwinii'' (''darwinii'' is the spelling used by Owen, but in modern times ''darwini'' is also often used; according to the [[International Rules of Zoological Nomenclature|Regulations of Zoological Nomenclature]], the former version is correct.<ref name="Iuliis et al. 2017">{{cite journal |last1=De Iuliis |first1=Gerardo |last2=Cartelle |first2=Cástor |last3=McDonald |first3=H. Gregory |last4=Pujos |first4=François |title=The mylodontine ground sloth Glossotherium tropicorum from the late Pleistocene of Ecuador and Peru |journal=Papers in Palaeontology |date=November 2017 |volume=3 |issue=4 |pages=613–636 |doi=10.1002/spp2.1088 |bibcode=2017PPal....3..613D |s2cid=135080382 |hdl=11336/64132 |hdl-access=free }}</ref>) He related the genus name to the molar-like teeth (from [[Greek language|Greek]] ''μυλη'' (''myle'') for "molar" and ''ὀδούς'' (''odoús'') for "tooth", thus translating as much as "molar tooth"), with the [[Specific name (zoology)|species epithet]] ''darwinii'' honoring Darwin as finder of the [[holotype|voucher specimen]]. As a second species besides ''M. darwinii'' Owen referred in his paper to ''M. harlani''. This form was based on a mandible and clavicle, both of which came from the Big Bone Lick in [[Boone County (Kentucky)|Boone County]] in the U.S. state of [[Kentucky]], and which [[Richard Harlan]] had already described in 1831 under the species assignment ''Megalonyx laqueatus''.<ref name="Harlan 1831">{{cite journal |id={{ProQuest|135712153}} |first1=Richard |last1=Harlan |title=Description of the jaws, teeth, and clavicle of the Megalonyx laqueatus |journal=Monthly American Journal of Geology and Natural Science |volume=1 |issue=2 |date=August 1831 |pages=74–76 }}</ref> Owen, however, recognized similarities in the construction of the mandible to his ''M. darwinii'' and renamed Harlan's form.<ref name="Owen 1840">Richard Owen: Fossil Mammalia. In: Charles Darwin (ed.): Zoology of the Voyage of HMS Beagle, under the command of Captain Fitzroy, during the years 1832 to 1836. Part I. Fossil Mammals. London, 1840, pp. 12-111 (pp. 63-73) ( biodiversitylibrary.org ).</ref> Harlan used an essay two years later to comment on Owen's choice of name regarding ''Mylodon,'' which he felt was not very descriptive. According to him, the name could be applied to almost any extinct mammalian form because almost all of them had the posterior molars. Moreover, the name would be inappropriate because, starting from the [[Latin]] version ''dens molaris'' for "molar tooth" and the second part of speech ''don'' (from ''dens'' for "tooth"), there is a duplication that would translate as "molar tooth-tooth".<ref name="Harlan 1842"/<ref name="Juan Carlos Fernicola 2009, pp. 147-159">{{cite journal |last1=Fernicola |first1=Juan Carlos |last2=Vizcaíno |first2=Sergio F. |last3=De Iuliis |first3=Gerardo |title=The fossil mammals collected byCharles Darwin in South America during his travels on board the HMS Beagle |journal=Revista de la Asociación Geológica Argentina |date=April 2009 |volume=64 |issue=1 |pages=147–159 |url=http://www.scielo.org.ar/scielo.php?pid=S0004-48222009000100016&script=sci_abstract&tlng=pt |citeseerx=10.1.1.1061.9082 }}</ref> Regardless, Owen's establishment of the genus ''Mylodon'' with two species resulted in the extinct sloth representative being distributed in both South and North America.<ref name="Juan Carlos Fernicola 2009, pp. 147-159"/><ref name="Vizcaino et al. 2009">{{cite journal |last1=Vizcaíno |first1=Sergio F. |last2=Fariña |first2=Richard A. |last3=Fernicola |first3=Juan Carlos |title=Young Darwin and the ecology and extinction of pleistocene south american fossil mammals |journal=Revista de la Asociación Geológica Argentina |date=April 2009 |volume=64 |issue=1 |pages=160–169 |url=http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0004-48222009000100017 }}</ref>

=== ''Glossotherium'', ''Grypotherium'' and ''Paramylodon'' ===
[[File:Glossotherium skull lithographic plate.jpg|thumb|right|Skull of ''[[Glossotherium]]'' with typical short and broad snout and open nasal cavity]]
Owen, in his 1840 work, established the genus ''Glossotherium'' in addition to ''Mylodon'', but without designation of a specific species. The basis here was a posterior skull fragment taken from the riverbed of the Arroyo Sarandi in the [[Uruguay]] department of [[Soriano Department|Soriano]]. In contrast to ''Mylodon'', for which Owen assumed a kinship proximity to the other large ground sloths known at the time, such as ''[[Megatherium]]'' or ''[[Megalonyx]]'', he placed ''Glossotherium'' in a series with the [[anteaters]] and with the [[pangolins]], respectively, and postulated an insectivorous lifestyle for the animals.<ref name="Owen 1840"/> Two years later, however, Owen discarded the name ''Glossotherium'' again. This occurred in the course of processing a nearly complete skeleton that had been discovered the year before in the flood plains of the [[Río de la Plata]] north of [[Buenos Aires]]. The largely intact skull was characterized by a short and broad snout and by a dentition consisting of a total of 18 teeth, of which the foremost tooth in each case showed a canine design. Based on the similarities in dental structure with the flat, molar-like teeth, Owen placed the skeleton in the genus ''Mylodon'' and introduced the new species ''M. robustus.'' The skull fragment that he had originally placed in ''Glossotherium'' he now associated with ''M. darwinii''.<ref name="Owen 1842">Richard Owen: Description of the skeleton of an extinct gigantic Sloth, Mylodon robustus, Owen, with observations on the osteology, natural affinities, and probable habitats of the Megatherioid quadrupeds in general. London, 1842, pp. 1-176 (especially p. 154) ( archive.org ).</ref> As a result of this study, three species of the genus ''Mylodon'' already existed in the 1840s.<ref name="Juan Carlos Fernicola 2009, pp. 147-159"/><ref name="mcafee2009">{{cite journal |last1=Mcafee |first1=Robert K. |title=Reassessment of the cranial characters of Glossotherium and Paramylodon (Mammalia: Xenarthra: Mylodontidae) |journal=Zoological Journal of the Linnean Society |date=April 2009 |volume=155 |issue=4 |pages=885–903 |doi=10.1111/j.1096-3642.2008.00468.x |doi-access=free }}</ref>

A skull including mandible found at [[Pergamino]] in Buenos Aires Province served the Danish zoologist [[Johannes Theodor Reinhardt]] (1816-1882) in 1879 as the basis for a comprehensive description. Characteristic of the skull was the narrow snout and a closed nasal arch, which was formed by the firm adhesion of the nasal bone to the middle jaw bone. Furthermore, the dentition consisted of a total of 16 teeth, the upper front canine-like tooth was reduced in each case, in the lower jaw, however, sat four molar-like teeth each. Reinhardt noticed similarities to ''M. darwinii'' in the construction of the lower jaw, but in the skull design his find deviated clearly from the broad-nosed ''M. robustus'' by the narrow snout. However, according to Reinhardt, there were matches in Owen's ''Glossotherium'' skull fragment with corresponding skull sections in ''M. robustus''. Based on the clear parallels between ''M. darwinii'' and his narrow-beaked skull finding, Reinhardt propagated the new genus ''Grypotherium'' with ''Grypotherium darwinii'' as the [[type species]].<ref name="Reinhardt 1879">Johannes Theodor Reinhardt: Beskrivelse af Hovedskallen af et Kæmpedovendyr, Grypotherium darwini. In: Det Kongelige Danske Videnskabernes Selskabs Skrifter. 5 Række. Naturvidenskabelig og Mathematisk Afdeling 12 (5), 1879, pp. 351–381 ( archive.org ).</ref> A different approach was taken by [[Florentino Ameghino]] (1854-1911) about ten years later. He confirmed in 1889, the separation of both ''M. darwinii'' and ''M. robustus'' not only at the species level, but also at the genus level. Deviating from Reinhardt, but agreeing with Owen, he considered the mandible of ''M. darwinii'' and the skull fragment of ''Glossotherium'' to belong together. Since in this scenario ''Glossotherium'' possessed [[principle of priority|priority]] over ''Mylodon'' (Owen mentioned the former over the latter in 1840) and ''Grypotherium,'' Ameghino introduced the species ''Glossotherium darwinii.'' In contrast, he left the status of ''M. robustus'' untouched.<ref name="Ameghino 1889">Florentino Ameghino: Contribución al conocimiento de los mamíferos fósiles de la República Argentina. In: Actas de la Academia Nacional de Ciencias. Volume 6, 1889, pp. 1-1027 (pp. 734-744).</ref> [[Arthur Smith Woodward]] (1864-1944), in turn, followed Reinhardt's reasoning. In a paper published in 1900, he presented findings from ground sloths of southern [[Patagonia]] and at the same time revised Charles Darwin's collection. In doing so, he equated the mandible of ''M. darwinii'' with Reinhardt's ''Grypotherium'' and subsequently recovered ''Grypotherium darwinii''. Smith Woodward assigned the skull fragment of ''Glossotherium'' to ''M. robustus'' by analogy with Reinhardt.<ref name="woodward1900"/><ref name="McDonald 1995">{{cite journal |last1=McDonald |first1=H. Gregory |title=Gravigrade xenarthrans from the early Pleistocene Leisey Shell Pit lA, Hillsborough County, Florida |journal=Bulletin of the Florida Museum of Natural History |volume=37 |issue=11 |year=1995 |pages=245–373 |doi=10.58782/flmnh.tdzu5337 |url=https://www.floridamuseum.ufl.edu/wp-content/uploads/sites/35/2017/03/Vol-37-No-11.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.floridamuseum.ufl.edu/wp-content/uploads/sites/35/2017/03/Vol-37-No-11.pdf |archive-date=2022-10-09 |url-status=live }}</ref><ref name="Juan Carlos Fernicola 2009, pp. 147-159" /><ref name="mcafee2009"/>

== Paleobiology ==
===Diet===
[[File:Mylodon model.jpg|thumb|left|Model in Cueva del Milodón Natural Monument where fossils were found in 1896]]
The mylodontids (particularly ''Mylodon'' itself) are often considered to be pronounced grazers because of their dental structure with flat chewing surfaces on the molar-like teeth. This is also supported by the high (hypsodont) tooth crowns and the wide mouth with numerous shapes. The ungulates are mostly used as analogous examples, in which shapes with high tooth crowns and broad-lipped mouths are usually grass-eating, such as various cattle, horses or the white rhinoceros. In contrast, those with low tooth crowns and narrow snouts such as the duiker or the black rhinoceros feed largely selective from various leaves and other soft vegetable foods. In contrast to other large mylodontid sloths such as ''Glossotherium'', ''Paramylodon'' or ''Lestodon'', the mouth of ''Mylodon'' is relatively narrow. A special feature is the closed nasal arch, which is heavily roughened in its front area and thus offers muscle attachment points for a mobile upper lip. Something similar can be said about individual depressions in the vicinity of the infraorbital foramen, which also functioned as starting points for individual muscle strands in the nose and lip area. Maybe ''Mylodon'' was more well-adapted to a mixed-vegetation diet, which was picked up with the help of a movable upper lip. The loss of the front teeth in the upper row of teeth also leads to the assumption that, comparable to cattle, there was a horn-like structure on the middle jawbone that could be used to pluck the food.<ref name="bargoetal2006b">{{cite journal |last1=Bargo |first1=M. Susana |last2=Toledo |first2=Néstor |last3=Vizcaíno |first3=Sergio F. |title=Muzzle of South American Pleistocene ground sloths (Xenarthra, Tardigrada) |journal=Journal of Morphology |date=February 2006 |volume=267 |issue=2 |pages=248–263 |doi=10.1002/jmor.10399 |pmid=16315216 |s2cid=39664746 }}</ref><ref name="bargo&vizcaino2008"/>

The entire anterior cranial structure of ''Mylodon'' is relatively solid, combined with a partially ossified nasal septum, it can be assumed that relatively high chewing forces acted when the food was chopped up. In contrast to the sometimes huge representatives of the [[Megatheriidae]], the joint between the lower jaw and the skull of the Mylodonts was relatively low, roughly at the chewing level of the teeth. The resulting decreasing lever arm of the masseter muscle experiences through the structure of the zygomatic arch, mainly of the descending process, a certain compensation, so that there should have been only minor differences to the Megatheria with regard to the biting force. The extended mandibular joint allows a wide freedom of movement when chewing. Against this, however, is the zygomatic arch, which is not closed and therefore could only withstand the opposing forces of the masseter and musculus pterygoideus to a limited extent. It can therefore be assumed that forwards and backwards directed chewing movements dominated in ''Mylodon''.<ref name="bargoetal2006b"/><ref name="bargo&vizcaino2008"/> The flat tooth crowns lead to a comparatively small size of the total available chewing surface. In ''Mylodon'', this amounts to a good 1320 mm<sup>2</sup> corresponding to other mylodonts of the same size. The Indian rhinoceros, which is comparable in terms of its dimensions, has, on the other hand, double to four times the value with 2660 to 5190 mm<sup>2</sup>. The situation is similar with the hippopotamus, the total surface area of which is between 3290 and 5410 mm<sup>2</sup>. The small total occlusal surface of the teeth in ''Mylodon'' probably resulted in a rather low processing capacity for the food in the mouth. This can result in either a high rate of fermentation in the gastrointestinal tract and/or a very slow metabolism concluded. The latter is the case with today's sloths. This is due to the long passage time of the food of up to a week through the large, multi-chambered stomach. It can be assumed that this also applies to the extinct sloths. Possibly this made the stomach of the mylodonts a functional equivalent to the complex stomach of the ruminants, whereby a long passage time of the food enabled efficient digestion, in which even more difficult to access nutrients could be provided, for example from foods with a greater fiber content. Such a digestive system could reduce the amount of processed food in the mouth and thus ultimately also have compensated for the small total chewing surface in ''Mylodon''.<ref name="vizcainoetal2006c">{{cite journal |last1=Vizcaíno |first1=Sergio F. |last2=Bargo |first2=M. Susana |last3=Cassini |first3=Guillermo H. |title=Dental occlusal surface area in relation to body mass, food habits and other biological features in fossil xenarthrans |journal=Ameghiniana |date=2006 |volume=43 |issue=1 |pages=11–26 |url=https://ameghiniana.org.ar/index.php/ameghiniana/article/view/735 }}</ref><ref name="vizcaino2009">{{cite journal |last1=Vizcaíno |first1=Sergio F. |title=The teeth of the 'toothless': novelties and key innovations in the evolution of xenarthrans (Mammalia, Xenarthra) |journal=Paleobiology |date=2009 |volume=35 |issue=3 |pages=343–366 |doi=10.1666/0094-8373-35.3.343 |bibcode=2009Pbio...35..343V |s2cid=86798959 }}</ref>

[[File:Mylodon darwini.png|thumb|Restoration of ''Mylodon darwini'' with an excrement and skin fragment.]]
Direct analysis of the food resources used is possible, among many other things, due to the numerous dung residues in the form of coprolites. These are available not only from the Cueva del Milodón in the Chilean part of Patagonia, but also from other caves. The coprolites of ''Mylodon'' have a diameter of up to 18 cm.<ref name="Borrero & Martin 2012">{{cite journal |last1=Borrero |first1=Luis Alberto |last2=Martin |first2=Fabiana María |title=Taphonomic observations on ground sloth bone and dung from Cueva del Milodón, Ultima Esperanza, Chile: 100 years of research history |journal=Quaternary International |date=November 2012 |volume=278 |pages=3–11 |doi=10.1016/j.quaint.2012.04.036 |bibcode=2012QuInt.278....3B }}</ref> Investigations of the plant residues showed 80 to 95% grasses and 5 to 20% [[sedges]]. Herbaceous plants, on the other hand, could only be detected in traces. Accordingly, ''Mylodon'' led, at least in southwestern Patagonia, a diet consisting almost exclusively of grasses. The food is reflected in the paleohabitat, as pollen analyzes show that the landscape at that time was tundra-like in character and was therefore almost free of trees with only a few low bushes. Occasional evidence of false beeches is interpreted as pollen carried by the wind.<ref name="markgraf1985">{{cite journal |last1=Markgraf |first1=Vera |title=Late Pleistocene Faunal Extinctions in Southern Patagonia |journal=Science |date=31 May 1985 |volume=228 |issue=4703 |pages=1110–1112 |doi=10.1126/science.228.4703.1110 |pmid=17737905 |bibcode=1985Sci...228.1110M |s2cid=26741329 }}</ref><ref name="heusseretal1992">Calvin J. Heusser, Luis A. Borrero and José A. Lanata: Late Glacial vegetation at Cueva del Mylodon. Anales del Instituto de la Patagonia (Ciencias Naturales series) 21, 1992, pp. 97-102</ref><ref name="villa-martinez&moreno2007">{{cite journal |last1=Villa-Martínez |first1=Rodrigo |last2=Moreno |first2=Patricio I. |title=Pollen evidence for variations in the southern margin of the westerly winds in SW patagonia over the last 12,600 years |journal=Quaternary Research |date=November 2007 |volume=68 |issue=3 |pages=400–409 |doi=10.1016/j.yqres.2007.07.003 |bibcode=2007QuRes..68..400V |s2cid=54974299 }}</ref>

A 2021 study on [[stable isotope ratio]]s concluded that ''Mylodon'' must have been at least sporadically omnivorous.<ref>{{cite journal |last1=Tejada |first1=Julia V. |last2=Flynn |first2=John J. |last3=MacPhee |first3=Ross |last4=O’Connell |first4=Tamsin C. |author4-link=Tamsin O'Connell |last5=Cerling |first5=Thure E. |last6=Bermudez |first6=Lizette |last7=Capuñay |first7=Carmen |last8=Wallsgrove |first8=Natalie |last9=Popp |first9=Brian N. |title=Isotope data from amino acids indicate Darwin's ground sloth was not an herbivore |journal=Scientific Reports |date=7 October 2021 |volume=11 |issue=1 |pages=18944 |doi=10.1038/s41598-021-97996-9 |pmid=34615902 |pmc=8494799 |bibcode=2021NatSR..1118944T |s2cid=238422083 }}</ref>

=== Locomotion ===
In general, large mylodonts are ground-dwelling animals. The lower section of the hind leg, which is very short compared to the upper, is also found in ''Mylodon'', whose tibia is 27 cm in length and only half as long as the thigh bone, 59 cm in length. In comparison, the Megatheriidae possess significantly longer lower leg portions, about the almost equally-proportioned ''[[Pyramiodontherium]]'' possessing to a 47 cm long shin to a 49 cm long femur. Possibly these differences in the hind leg structure result in much more agile locomotion in the Megatheria in relation to the mylodonts.<ref name="deiuliisetal2004">{{cite journal |last1=De Iuliis |first1=Gerardo |last2=Ré |first2=Guillermo H. |last3=Vizcaíno |first3=Sergio F. |title=The Toro Negro megatheriine (Mammalia, Xenarthra): a new species of Pyramiodontherium and a review of Plesiomegatherium |journal=Journal of Vertebrate Paleontology |date=25 March 2004 |volume=24 |issue=1 |pages=214–227 |doi=10.1671/17.1 |bibcode=2004JVPal..24..214D |s2cid=85178982 }}</ref> Similar to other large ground sloths, the hand of ''Mylodon'' made contact with the ground with the outer side edge and thus sat up rotated. This is indicated by the long metacarpal bones of the external digits and the decreasing number of phalanges on them. The special hand position protected the long claws of the inner digits, which did not penetrate the ground while walking. A functionally similar but fundamentally different hand position can be found in the ankle duct of the distantly related present-day great anteater. The elbow joint was pointed slightly outwards when standing on four feet and the arms were thus angled slightly inwards, which is evident from the position of the olecranon yields. The hands came to rest slightly within the width of the elbow. Such an orientation of the arms can effectively support the large mass of ''Mylodon''. As a result, the hands would also be in a line with the feet, which is also conveyed, among other things, by footprints from ''Paramylodon''. The laterally limited articular surface of the femoral head severely restricted the mobility of the hindlimbs. The same applies to the forearm, the straight spoke with the laterally elongated head of which did not allow any major rotational movements. These features can be interpreted as adaptations to a purely [[terrestrial animal|terrestrial]] lifestyle. Finally, the muscle attachment points on the first cervical vertebra referenced, which are more developed than for example with ''Paramylodon''. Correspondingly, the occipital joint surfaces are also somewhat further apart. Both can be interpreted as meaning that the more massive skull of ''Mylodon'', caused by the lengthening of the snout region, required greater muscle support.<ref name="kraglievich1934"/><ref name="mcafee2016"/>

For some of the mylodonts of South America, such as ''Glossotherium'', a partially burrowing way of life is being reconstructed, which results from the construction of the foreleg, among other things. An indicator for this is the upper articular process (olecranon) of the ulna. The longer the olecranon, the higher the leverage of the forearm, since more attachment surface is available for the forearm muscles. In ''Glossotherium'', the olecranon takes up up to 35% of the total length of the ulna. The resulting ability to dig would be comparable to that of the ''[[Tolypeutes]]'' armadillos, which seldom build their own burrows, but can do so.<ref name="bargoetal2000">{{cite journal |last1=Bargo |first1=M. Susana |last2=Vizcaíno |first2=Sergio F. |last3=Archuby |first3=Fernando M. |last4=Blanco |first4=R. Ernesto |title=Limb bone proportions, strength and digging in some Lujanian (Late Pleistocene-Early Holocene) mylodontid ground sloths (Mammalia, Xenarthra) |journal=Journal of Vertebrate Paleontology |date=25 September 2000 |volume=20 |issue=3 |pages=601–610 |doi=10.1671/0272-4634(2000)020[0601:LBPSAD]2.0.CO;2 |s2cid=86036390 }}</ref> The previous analyses for ''Mylodon'' resulted in a much shorter olecranon, which accounts for only about 22% of the total length of the ulna. However, the fact that proportional estimates for ''Mylodon'' refer to a not fully grown specimen is problematic.<ref name="haroetal2016">{{cite journal |last1=Haro |first1=José A. |last2=Tauber |first2=Adan A. |last3=Krapovickas |first3=Jerónimo M. |title=The manus of mylodon darwinii Owen (Tardigrada, Mylodontidae) and its phylogenetic implications |journal=Journal of Vertebrate Paleontology |date=2 September 2016 |volume=36 |issue=5 |pages=e1188824 |doi=10.1080/02724634.2016.1188824 |bibcode=2016JVPal..36E8824H |s2cid=89036115 |url=https://figshare.com/articles/dataset/The_manus_of_i_Mylodon_darwinii_i_Owen_Tardigrada_Mylodontidae_and_its_phylogenetic_implications/3443405 |hdl=11336/179728 |hdl-access=free }}</ref> Other clues can be derived from the construction of the hand. In ''Mylodon'', for example, the metacarpal bones of the second and third ray are very delicate, in contrast to ''Glossotherium''. A weakly pronounced central ray does not seem to support a digging activity, as this is usually most strongly developed in underground mammals. However, the distal articular facet of the third metacarpal bone is flat, which means that the middle finger is generally stiff and stable. The same articulation surface on the second metacarpal is significantly more rounded and thus supports greater mobility of the finger when gripping. This obviously resulted in functional differences between the individual rays of the hand. The rare signs of wear and tear on the last phalanx, which are isolated from the Cueva del Milodón several times, can serve as an additional indicator of digging activities.<ref name="mcafee2016"/><ref name="haroetal2016"/>

=== Predation and Parasites ===
Especially in southern and southwestern Patagonia, numerous bone changes in finds of ''Mylodon'' can be proven to be caused by predatory animals. This includes, above all, the remains from the Cueva del Milodón in southwestern Chile. Some caves in their immediate vicinity, such as Cueva Lago Sofía 4 and Cueva Chica, are interpreted as clumps of predators.<ref name="borreroetal1997">{{cite journal |last1=Borrero |first1=Luis Alberto |last2=Martín |first2=Fabiana M. |last3=Prieto |first3=Alfredo |title=La cueva Lago Sofía 4, Ultima Esperanza, Chile: una madriguera de felino del pleistoceno tardío |trans-title=Lago Sofía 4 cave, Ultima Esperanza, Chile: a feline burrow from the late Pleistocene |language=es |journal=Anales del Instituto de la Patagonia. Serie Ciencias Humanas |date=1997 |volume=25 |pages=103–122 }}</ref><ref name="Martin et al. 2013"/> The same applies to the Cueva del Puma or the Cueva Fell in the Pali-Aike area of southern Chile. Some of the caves mainly contain smaller skeletal elements such as hand and foot bones or bone plates, which indicate that only part of the carcass was carried into the shelter. Whether this is the result of direct foraging or scavenging cannot be determined in many cases. Other caves, in turn, contained a larger proportion of young ''Mylodon'' animals.<ref name="martin2008">{{cite journal |last1=Martin |first1=Fabiana M. |title=Bone-Crunching Felids at the End of the Pleistocene in Fuego-Patagonia, Chile. |journal=Journal of Taphonomy |date=2008 |volume=6 |issue=3–4 |pages=337–372 }}</ref><ref name=Borrero2009/> The largest predators occurring at that time are the [[Puma (genus)|puma]] and the [[jaguar]], as well as the saber-toothed cat ''[[Smilodon populator]]'' and the extinct bear ''[[Arctotherium]]''. The latter two could have reconstructed body weights of over 400 kg, with prey sizes between 1 and 2 t being assumed for the saber-toothed cat, which makes ''Smilodon'' a likely predator of ''Mylodon''.<ref name="manzuettietal2020">{{cite journal |last1=Manzuetti |first1=Aldo |last2=Perea |first2=Daniel |last3=Jones |first3=Washington |last4=Ubilla |first4=Martín |last5=Rinderknecht |first5=Andrés |title=An extremely large saber-tooth cat skull from Uruguay (late Pleistocene–early Holocene, Dolores Formation): body size and paleobiological implications |journal=Alcheringa: An Australasian Journal of Palaeontology |date=2 April 2020 |volume=44 |issue=2 |pages=332–339 |doi=10.1080/03115518.2019.1701080 |bibcode=2020Alch...44..332M |s2cid=216505747 }}</ref><ref name="martin2008"/><ref name=Borrero2009/><ref name="prevostietal2013">{{cite journal |last1=Prevosti |first1=Francisco J. |last2=Martin |first2=Fabiana M. |title=Paleoecology of the mammalian predator guild of Southern Patagonia during the latest Pleistocene: Ecomorphology, stable isotopes, and taphonomy |journal=Quaternary International |date=August 2013 |volume=305 |pages=74–84 |doi=10.1016/j.quaint.2012.12.039 |bibcode=2013QuInt.305...74P |hdl=11336/84524 |hdl-access=free }}</ref>

In various coprolites produced by ''Mylodon'', eggs of [[nematodes]] are preserved. The eggs are ovaloid in shape with lengths of almost 50 μm in length and 29 μm in thickness.<ref name="ringuelet1957">{{cite journal |last1=Ringuelet |first1=Raúl A. |title=Restos de probables huevos de nematodes en el estiercol del edentado extinguido Mylodon listai (Ameghino) |trans-title=Remains of probable nematode eggs in the manure of the extinct edentulous Mylodon Listai (Ameghino) |journal=Ameghiniana |date=1957 |volume=1 |issue=1–2 |pages=15–16 |url=https://www.ameghiniana.org.ar/index.php/ameghiniana/article/view/1084 |language=es }}</ref> In addition, individual beetles could be detected.<ref name="Borrero & Martin 2012"/>

== Extinction ==
''Mylodon'' became extinct 12-10,000 years ago at the end of the Pleistocene as part of the [[Late Pleistocene extinctions|Late Pleistocene megafauna extinctions]], along with all other mainland ground sloths and most large animals in the Americas. The timing coincides with the [[Settlement of the Americas|arrival of humans in the Americas]], as well as climatic change.<ref>{{Cite journal |last1=Villavicencio |first1=Natalia A. |last2=Lindsey |first2=Emily L. |last3=Martin |first3=Fabiana M. |last4=Borrero |first4=Luis A. |last5=Moreno |first5=Patricio I. |last6=Marshall |first6=Charles R. |last7=Barnosky |first7=Anthony D. |date=February 2016 |title=Combination of humans, climate, and vegetation change triggered Late Quaternary megafauna extinction in the Última Esperanza region, southern Patagonia, Chile |journal=Ecography |language=en |volume=39 |issue=2 |pages=125–140 |doi=10.1111/ecog.01606 |issn=0906-7590|doi-access=free |bibcode=2016Ecogr..39..125V }}</ref> There is evidence that humans exploited ''Mylodon'' for food. At [[Fell's cave]] (Cueva Fell) in Chilean Patagonia, fractured and burned bones of ''Mylodon darwinii'' have been found in association with human artefacts, dating to around 12,766–12,354 calendar years [[Before Present]] (BP). At [[Piedra Museo]] in Argentine Patagonia, bones of ''Mylodon'' are found in association with human artefacts, dating to around 15,517–12,352 cal yr BP. This exploitation may have been a factor in its extinction.<ref name=":2">{{Cite journal |last1=Bampi |first1=Hugo |last2=Barberi |first2=Maira |last3=Lima-Ribeiro |first3=Matheus S. |date=December 2022 |title=Megafauna kill sites in South America: A critical review |url=https://linkinghub.elsevier.com/retrieve/pii/S0277379122004826 |journal=Quaternary Science Reviews |language=en |volume=298 |pages=107851 |doi=10.1016/j.quascirev.2022.107851|bibcode=2022QSRv..29807851B |s2cid=253876769 }}</ref>

== References ==
{{Reflist}}

{{Portal|Argentina|Chile|Paleontology|Prehistoric mammals}}
{{Pilosan genera|P.}}
{{Taxonbar|from=Q310869}}

[[Category:Prehistoric sloths]]
[[Category:Pleistocene xenarthrans]]
[[Category:Prehistoric placental genera]]
[[Category:Pleistocene first appearances]]
[[Category:Holocene extinctions]]
[[Category:Pleistocene mammals of South America]]
[[Category:Lujanian]]
[[Category:Ensenadan]]
[[Category:Uquian]]
[[Category:Pleistocene Argentina]]
[[Category:Fossils of Argentina]]
[[Category:Pleistocene Chile]]
[[Category:Fossils of Chile]]
[[Category:Fossil taxa described in 1840]]
[[Category:Taxa named by Richard Owen]]