Editing Megatherium (section)

=== Skull and jaws ===
[[File:Megatherium skull.png|thumb|270x270px|Skull and lower jaws of ''M. americanum'' (note: nasal septum is broken) Scale bar = 10 cm, ~ 4 inches]]
The head of ''Megatherium'' is relatively small compared to body size.<ref name=":5" /> The skull is roughly cylindrical in shape, with the cranial region of the skull being narrow. The [[Jugal bone|jugal]] bone of ''M. americanum'' has strongly developed ascending and descending [[Process (anatomy)|processes]].<ref name=":4">Bargo, M.S. 2001. [https://www.app.pan.pl/archive/published/app46/app46-173.pdf The ground sloth ''Megatherium americanum'': Skull shape, bite forces,  and diet]. – ''Acta Palaeontologica Polonica'' 46,2, 173–192.</ref> The skull of ''M. americanum'' has a relatively small [[cranial cavity]] (and thus brain) relative to skull size, with the skull having extensive [[Sinus (anatomy)|sinus]] spaces.<ref>{{Citation |last1=Boscaini |first1=Alberto |title=The Endocranial Cavities of Sloths (Xenarthra, Folivora): Insights from the Brain Endocast, Bony Labyrinth, and Cranial Sinuses |date=2023 |work=Paleoneurology of Amniotes |pages=737–760 |editor-last=Dozo |editor-first=María Teresa |url=https://link.springer.com/10.1007/978-3-031-13983-3_19 |access-date=2024-05-14 |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-031-13983-3_19 |isbn=978-3-031-13982-6 |last2=Iurino |first2=Dawid A. |last3=Sardella |first3=Raffaele |last4=Gaudin |first4=Timothy J. |last5=Pujos |first5=François |editor2-last=Paulina-Carabajal |editor2-first=Ariana |editor3-last=Macrini |editor3-first=Thomas E. |editor4-last=Walsh |editor4-first=Stig}}</ref> In many species of ''Megatherium'', the lower jaw is relatively deep, which served to accommodate the very long hypselodont (evergrowing) teeth,<ref name=":3" /> which are considerably proportionally longer than those of other ground sloths. Like other ground sloths, the number of teeth in the jaw is reduced to 5 and 4 teeth in each half of the upper and lower jaws, respectively, and the teeth lack enamel. The teeth of ''Megatherium americanum'' have sharp crests separated by v-shaped valleys, which interlock with the teeth on the opposing jaw.<ref name=":4" /> These teeth were self-sharpening, akin to rodent incisors.<ref name=":13">{{Cite journal |last1=Green |first1=Jeremy L. |last2=Kalthoff |first2=Daniela C. |date=2015-08-03 |title=Xenarthran dental microstructure and dental microwear analyses, with new data for Megatherium americanum (Megatheriidae) |url=https://academic.oup.com/jmammal/article-lookup/doi/10.1093/jmammal/gyv045 |journal=Journal of Mammalogy |language=en |volume=96 |issue=4 |pages=645–657 |doi=10.1093/jmammal/gyv045 |issn=0022-2372}}</ref> The skull of ''M. americanum'' has a relatively narrow snout/muzzle with a [[Ossification|ossified]] [[nasal septum]], and is suggested to have had a thick [[Prehensility|prehensile]] upper lip, similar to that of the living [[black rhinoceros]], which compensated for the lack of teeth at the front of the jaws.<ref name=":7">{{Cite journal |last1=Bargo |first1=M. Susana |last2=Toledo |first2=Néstor |last3=Vizcaíno |first3=Sergio F. |date=February 2006 |title=Muzzle of South American Pleistocene ground sloths (Xenarthra, Tardigrada) |url=https://onlinelibrary.wiley.com/doi/10.1002/jmor.10399 |journal=Journal of Morphology |language=en |volume=267 |issue=2 |pages=248–263 |doi=10.1002/jmor.10399 |issn=0362-2525 |pmid=16315216}}</ref> The morphology of the [[hyoid bones]] in ''Megatherium'' suggests that they were relatively rigid, this along with the short distance between the hyoid and the [[mandibular symphysis]] (the joint connecting the two halves of the lower jaw) suggests that the tongue had limited ability to protrude, and thus ''Megatherium'' did not have a long prehensile tongue, contrary to what was often historically suggested.<ref>{{cite journal |last1=Perez |first1=L. M. |last2=Toledo |first2=N. |last3=De Lullis |first3=G. |last4=Bargo |first4=M. S. |last5=Vizcaino |first5=S. F. |year=2010 |title=Morphology and Function of the Hyoid Apparatus of Xenarthran Fossils (Mammalia) |journal=Journal of Morphology |volume=271 |issue=9 |pages=1119–1133 |doi=10.1002/jmor.10859 |pmid=20730924 |s2cid=8106788}}</ref>  The skull and jaws of ''M. americanum'' show adaptation to powerful vertical biting.<ref name=":4" /> ''M. americanum'' and ''M. altiplanicum'' are distinguished from species of the subgenus ''Pseudomegatherium'' by the fusion of the [[maxilla]] and [[premaxilla]], while members of ''Pseudomegatherium'' are distinguished from those species by their flat [[occipital condyles]].<ref name="Pujos2006" />