Editing Mylodon (section)

== 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"/>