Editing Ground sloth (section)

== Families ==
[[Paleontologist]]s assign more than 80&nbsp;[[genera]] of ground sloths to multiple [[family (biology)|families]].<ref>Modified from McKenna & Bell (1997)</ref>

=== Megalonychidae ===
{{Main|Megalonychidae}}
The [[Megalonychidae|megalonychid]] ground sloths first appeared in the [[Eocene|Late Eocene]], about 35&nbsp;million years ago, in Patagonia. Megalonychids first reached North America by island-hopping, prior to the formation of the [[Isthmus of Panama]]. Some lineages of megalonychids increased in size as time progressed. The first species of these were small and may have been partly tree-dwelling, whereas the [[Pliocene]] (about 5 to 2&nbsp;million years ago) species were already approximately half the size of the huge [[Late Pleistocene]] ''[[Megalonyx jeffersonii]]'' from the [[Quaternary glaciation|last ice age]]. Some West Indian island species were as small as a large cat; their dwarf condition typified both tropical adaptation and their restricted island environment.  This small size also enabled them a degree of arboreality.<ref name="J.L. White 1993">J.L. White (1993)</ref>

''[[Megalonyx]]'', which means "giant claw", was a widespread North American genus that lived past the close of the [[Last glacial period|last (Wisconsin) glaciation]], when so many large mammals died out.  Remains have been found as far north as Alaska<ref>{{cite journal |last=Stock |first=C. |title=A ground sloth in Alaska |journal=[[Science (journal)|Science]] | volume = 95 |issue = 2474 |pages = 552–553 |publisher=[[American Association for the Advancement of Science|AAAS]] |date=29 May 1942 |doi=10.1126/science.95.2474.552 |pmid=17790868 |bibcode=1942Sci....95..552S }}<!--| access-date = 10 October 2009--></ref> and the [[Yukon]].<ref name=Harrington/><ref>{{cite journal | last = McDonald | first = H.G. | author2 = Harington, C.R. | author3 = de&nbsp;Iuliis, G. | title = The Ground Sloth Megalonyx from Pleistocene Deposits of the Old Crow Basin, Yukon, Canada | journal = Arctic | volume = 53 | issue = 3 | pages = 213–220 | publisher = The Arctic Institute of North America | location = Calgary, Alberta | date = September 2000 | url = http://pubs.aina.ucalgary.ca/arctic/Arctic53-3-213.pdf | access-date = 16 August 2008 | doi = 10.14430/arctic852 | archive-date = 3 July 2020 | archive-url = https://web.archive.org/web/20200703013709/http://pubs.aina.ucalgary.ca/arctic/Arctic53-3-213.pdf | url-status = dead }}</ref> Ongoing excavations at Tarkio Valley in southwestern [[Iowa]] may reveal something of the familial life of ''Megalonyx''. An adult was found in direct association with two juveniles of different ages, suggesting that adults cared for young of different generations.<ref>Semken and Brenzel, http://slothcentral.com/?page_id=2 {{Webarchive|url=https://web.archive.org/web/20090101073804/http://slothcentral.com/?page_id=2 |date=2009-01-01 }}</ref><ref>{{cite journal | last1 = Semken | last2 = Brenzel | year = 2007 | title = One Sloth Becomes Three | journal=Newsletter of the Iowa Archeological Society | volume = 57 | page = 1 }}</ref>

The earliest known North American megalonychid, ''[[Pliometanastes|Pliometanastes protistus]]'', lived in the southern U.S. about 9&nbsp;million years ago and is believed to have been the predecessor of ''Megalonyx''. Several species of ''Megalonyx'' have been named; in fact it has been stated that "nearly every good specimen has been described as a different species".<ref name=Harrington>Harrington (1993)</ref> A broader perspective on the group, accounting for age, sex, individual and geographic differences, indicates that only three species are valid (''M. leptostomus'', ''M. wheatleyi'', and ''M. jeffersonii'') in the late Pliocene and Pleistocene of North America,<ref>Kurtén & Anderson, 1980, p. 136.</ref> although work by McDonald lists five species.
Jefferson's ground sloth has a special place in modern [[paleontology]], for [[Thomas Jefferson]]'s letter on ''Megalonyx'', read before the [[American Philosophical Society]] of [[Philadelphia]] in August&nbsp;1796, marked the beginning of [[vertebrate]] paleontology in North America.<ref name=Harrington/> When [[Lewis and Clark]] set out, Jefferson instructed Meriwether Lewis to keep an eye out for ground sloths. He was hoping they would find some living in the Western range. ''Megalonyx jeffersonii'' was appropriately named after Thomas Jefferson.<ref name=Harrington/>

=== Megatheriidae ===
{{Main|Megatheriidae}}
[[Image:Eremotherium.jpg|thumb|right|Fossil ''[[Eremotherium]]'' skeleton, [[National Museum of Natural History]], Washington, DC.]]
The [[Megatheriidae|megatheriid]] ground sloths are relatives of the megalonychids; these two families, along with the family Nothrotheriidae, form the [[infraorder]] [[Megatheria]]. Megatheriids appeared later in the Oligocene, some 30&nbsp;million years ago, also in South America. The group includes the heavily built ''[[Megatherium]]'' (given its name 'great beast' by [[Georges Cuvier]]<ref>G. Cuvier (1796)</ref>) and ''[[Eremotherium]],'' which are the largest known ground sloths, thought to have had body masses of 3.5-4 tons.<ref name=":4">{{Cite journal |last=McDonald |first=H. Gregory |date=2023-06-06 |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 |issn=2073-445X|doi-access=free }}</ref> The skeletal structure of these ground sloths indicates that the animals were massive.  Their thick bones and even thicker joints (especially those on the hind legs) gave their appendages tremendous power that, combined with their size and fearsome claws, provided a formidable defense against predators.

The earliest megatheriid in North America was ''Eremotherium eomigrans'' which arrived 2.2&nbsp;million years ago, after crossing the recently formed [[Panama]]nian land bridge. With more than five tons in weight, 6&nbsp;meters in length, and able to reach as high as {{convert|17|ft|m}}, it was larger than an [[African bush elephant]] bull. Unlike relatives, this species retained a [[plesiomorphic]] extra claw. While other species of ''Eremotherium'' had four fingers with only two or three claws, ''E. eomigrans'' had five fingers, four of them with claws up to nearly a foot long.<ref>De Iuliis and Cartelle (1999)</ref>

===Nothrotheriidae===
{{Main|Nothrotheriidae}}
Recently recognized, ground sloths of [[Nothrotheriidae]] are often associated with those of the [[Megatheriidae]], and together the two form the superfamily Megatherioidea. The most prominent members of the group are the South American genus ''[[Thalassocnus]]'', known for being aquatic, and ''[[Nothrotheriops]]'' from North America.

The last ground sloths in North America belonging to ''Nothrotheriops'' died so recently that their [[subfossil]] dung has remained undisturbed in some caves. One of the skeletons, found in a [[lava tube]] (cave) at [[Aden Crater]], adjacent to [[Kilbourne Hole]], [[New Mexico]], still had skin and hair preserved, and is now at the Yale [[Peabody Museum of Natural History|Peabody Museum]]. The largest samples of ''Nothrotheriops'' dung can be found in the collections of the Smithsonian Museum. Another ''Nothrotheriops'' was excavated at [[Shelter Cave]], also in [[Doña Ana County]], [[New Mexico]].{{citation needed|date=May 2014}}

=== Mylodontidae ===
{{Main|Mylodontidae}}
[[File:Paramylodon fossil at Texas Memorial Museum.jpg|thumb|right|''[[Paramylodon harlani]]'', [[Texas Memorial Museum]], [[University of Texas at Austin]]]]
The [[Mylodontidae|mylodontid]] ground sloths together with their relatives the scelidotheriids form the [[Mylodontoidea]], the second radiation of ground sloths. The discovery of their fossils in caverns associated with human occupation led some early researchers to theorize that the early humans built [[corral]]s when they could procure a young ground sloth, to raise the animal to butchering size.<ref>A. S. Woodward (1900)</ref> However, radiocarbon dates do not support simultaneous occupation of the site by humans and sloths.<ref name = "explained">{{cite journal | last = Naish | first = Darren | title = Fossils explained 51: Sloths | journal=Geology Today | volume = 21 | issue = 6 | pages = 232–238 | publisher=[[Geologists' Association]], [[Geological Society of London]] and [[Blackwell Publishing]] | date = 28 Nov 2005 | url = http://www3.interscience.wiley.com/journal/118652140/abstract | archive-url = https://archive.today/20121008120854/http://www3.interscience.wiley.com/journal/118652140/abstract | url-status = dead | archive-date = 8 October 2012 | doi = 10.1111/j.1365-2451.2005.00538.x  | s2cid = 85808869 | access-date = 29 January 2009| url-access = subscription }}</ref> [[Subfossil]] remains like coproliths, fur and skin have been discovered in some quantities. 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">{{cite journal |last=Bell |first=C.M. |title=Did elephants hang from trees? - the giant sloths of South America |journal=Geology Today |volume=18 |issue=2 |year=2002 |pages=63–66 (see p.&nbsp;66) |doi=10.1046/j.1365-2451.2002.00334.x|bibcode=2002GeolT..18...63B |s2cid=130426084 }}</ref><ref name = "TRCenter">{{cite web |url= https://www.theodorerooseveltcenter.org/Research/Digital-Library/Record?libID=o211307|title= Letter from Theodore Roosevelt to George Herbert Sherwood|last= Roosevelt|first= T.R.|date= 1915-01-04|website= theodorerooseveltcenter.org|publisher= [[Dickinson State University]]|access-date= 2019-10-12}}</ref><ref name = "AMNH">{{cite web |url= https://www.amnh.org/exhibitions/permanent/south-american-peoples/roosevelt-collection |title= Roosevelt Collections |website= amnh.org/exhibitions |publisher=[[American Museum of Natural History]] |access-date=2019-10-12}}</ref><ref name= "Warren2015">{{cite web |url=https://www.davidwarrenonline.com/2015/05/28/the-ground-sloth/ |title=The ground sloth |last=Warren |first=D. |date=2016-05-28 |website=Essays in Idleness |access-date= 2019-10-12}}</ref> Mylodontids are the only ground sloths confirmed to have had [[osteoderms]] embedded within their skin, though osteoderms were only present in a handful of genera and absent in many others.<ref>{{Cite journal |last=McDonald |first=H. Gregory |date=December 2018 |title=An Overview of the Presence of Osteoderms in Sloths: Implications for Osteoderms as a Plesiomorphic Character of the Xenarthra |url=http://link.springer.com/10.1007/s10914-017-9415-8 |journal=Journal of Mammalian Evolution |language=en |volume=25 |issue=4 |pages=485–493 |doi=10.1007/s10914-017-9415-8 |s2cid=254697023 |issn=1064-7554|url-access=subscription }}</ref>

The largest mylodontid is ''[[Lestodon]]'', with an estimated mass of {{Convert|3400-4100|kg|lb}}.<ref>{{Cite journal |last1=Tomassini |first1=Rodrigo L. |last2=Montalvo |first2=Claudia I. |last3=Garrone |first3=Mariana C. |last4=Domingo |first4=Laura |last5=Ferigolo |first5=Jorge |last6=Cruz |first6=Laura E. |last7=Sanz-Pérez |first7=Dánae |last8=Fernández-Jalvo |first8=Yolanda |last9=Cerda |first9=Ignacio A. |date=2020-07-02 |title=Gregariousness in the giant sloth Lestodon (Xenarthra): multi-proxy approach of a bonebed from the Last Maximum Glacial of Argentine Pampas |journal=Scientific Reports |language=en |volume=10 |issue=1 |page=10955 |doi=10.1038/s41598-020-67863-0 |pmid=32616813 |pmc=7331707 |bibcode=2020NatSR..1010955T |issn=2045-2322|hdl=10261/233402 |hdl-access=free }}</ref>

=== Scelidotheriidae ===
{{Main|Scelidotheriidae}}
The ground sloth family [[Scelidotheriidae]] was demoted in 1995 to the subfamily Scelidotheriinae within Mylodontidae.<ref>{{cite web |url=https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=83047 |website=PaleoBiology Database |title=Scelidotheriinae, basic info}}</ref><ref name="Gaudin_1995">{{cite journal |last=Gaudin |first=T.J. |date=1995-09-14 |title=The Ear Region of Edentates and the Phylogeny of the Tardigrada (Mammalia, Xenarthra) |journal=Journal of Vertebrate Paleontology |volume=15 |issue=3 |pages=672–705 |doi=10.1080/02724634.1995.10011255 |jstor=4523658|bibcode=1995JVPal..15..672G }}<!--| access-date = 2013-06-19 --></ref> Based on collagen sequence data showing that its members are more distant from other mylodontids than [[Choloepodidae]], it was elevated back to full family status in 2019.<ref name="Presslee2019" /> Together with Mylodontidae, the enigmatic ''[[Pseudoprepotherium]]'' and [[two-toed sloth]]s, the scelidotheriids form the superfamily Mylodontoidea. ''[[Chubutherium]]'' is an ancestral and very plesiomorphic member of this subfamily and does not belong to the main group of closely related genera, which include ''[[Scelidotherium]]'' and ''[[Catonyx]]''.

===Phylogeny===
The following sloth family phylogenetic tree is based on collagen and mitochondrial DNA sequence data (see Fig.&nbsp;4 of Presslee ''et al.''., 2019).<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&nbsp;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. |display-authors=6 |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= http://eprints.whiterose.ac.uk/147061/1/5426_3_merged_1554730549.pdf}}</ref>

{{clade | style = font-size: 100%;line-height:100%
| label1 =[[Folivora]]
|1={{clade
  |label1={{extinct}} [[Megalocnidae]]
  |sublabel1={{small|(Caribbean sloths)}}
  |1={{clade
    |1={{extinct}} ''[[Neocnus|Neocnus dousman]]''
    |2={{clade
      |1={{clade
        |1={{extinct}} ''[[Parocnus|Parocnus serus]]''
        |2={{extinct}} ''[[Neocnus|Neocnus comes]]''
      }}
      |2={{extinct}} ''[[Acratocnus|Acratocnus ye]]''
    }}
  }}
  |2={{clade
    |1={{clade
      |label1=Megatherioidea
 <!-- |grouplabelstyle1=vertical-align:left;
      |grouplabel1={{clade label|'''Megatherioidea'''|color=red|width=8em}}
      |bar1=red   -->
      |1={{clade
        |1={{clade
          |label1 ={{extinct}} [[Nothrotheriidae]]
          |1={{extinct}} ''[[Nothrotheriops shastensis]]''
          |label2 ={{extinct}} [[Megatheriidae]]
          |2={{extinct}} ''[[Megatherium americanum]]''
        }}
        |2={{clade
          |label1 ={{extinct}} [[Megalonychidae]]
          |1={{extinct}} ''[[Megalonyx jeffersoni]]''
          |label2 =[[Bradypodidae]]
          |sublabel2 = {{small| (three-fingered sloths) }}
          |2=[[Bradypodidae|5&nbsp;living spp.]]
        }}
      }}
      |label2=Mylodontoidea
 <!-- |grouplabel2={{clade label|'''Mylodontoidea'''|color=green|width=7.5em}}
      |bar2=green  --> 
      |2={{clade
        |1={{clade
          |label1 ={{extinct}} [[Scelidotheriidae]]
          |1={{clade
            |1={{extinct}} ''[[Scelidotherium]]'' sp.
            |2={{extinct}} ''[[Scelidodon]]'' sp.
          }}
        }}
        |2={{clade
          |label1 =[[Choloepodidae]]
          |sublabel1={{small| (two-fingered sloths) }}
          |1=[[Choloepodidae|2&nbsp;living spp.]]
          |label2 ={{extinct}} [[Mylodontidae]]
          |2={{clade
            |1={{extinct}} ''[[Lestodon armatus]]''
            |2={{clade
              |1={{extinct}} ''[[Paramylodon harlani]]''
               |2={{clade
                |1={{extinct}} ''[[Mylodon darwinii]]''
                |2={{extinct}} ''[[Glossotherium|Glossotherium robustus]]''
              }}
            }}
          }}
        }}
      }}
    }}
  }}
}}
}}