Editing Primate (section)

===Head===
[[File:Primate skull series with legend cropped.png|thumb|Primate skulls showing [[postorbital bar]], and increasing brain sizes]]
The primate skull has a large, domed [[Skull|cranium]], which is particularly prominent in [[Simian|anthropoids]]. The cranium protects the large brain, a distinguishing characteristic of this group.<ref name="pough" /> The endocranial volume (the volume within the skull) is three times greater in [[human]]s than in the greatest nonhuman primate, reflecting a larger brain size.<ref name="aiello" /> The mean endocranial volume is 1,201 cubic centimeters in humans, 469&nbsp;cm<sup>3</sup> in [[gorilla]]s, 400&nbsp;cm<sup>3</sup> in [[chimpanzee]]s and 397&nbsp;cm<sup>3</sup> in [[orangutan]]s.<ref name="aiello">{{cite book |author1=Aiello, L. |author2=Dean, C. |name-list-style=amp | year=1990 | title=An Introduction to Human Evolutionary Anatomy |url=https://archive.org/details/introductiontohu00aiel | publisher=Academic Press | pages=[https://archive.org/details/introductiontohu00aiel/page/193 193] | isbn=0-12-045590-0}}</ref> The primary evolutionary trend of primates has been the elaboration of the brain, in particular the [[neocortex]] (a part of the [[cerebral cortex]]), which is involved with [[sense|sensory perception]], generation of [[motor cortex|motor commands]], spatial reasoning, [[consciousness|conscious thought]] and, in humans, [[language]].<ref name="britannica" /> While other mammals rely heavily on their [[Olfaction|sense of smell]], the arboreal life of primates has led to a [[Somatosensory system|tactile]], [[Visual perception|visually]] dominant sensory system,<ref name="britannica" /> a reduction in the olfactory region of the brain and increasingly complex social behavior.<ref name="adw">{{cite web | url=http://animaldiversity.ummz.umich.edu/site/accounts/information/Primates.html | title="Primates" (On-line) |publisher=Animal Diversity Web | author=Myers, P. | year=1999 | access-date=2008-06-03}}</ref> The visual acuity of [[human]]s and other [[hominid]]s is exceptional; they have the most [[Spatial resolution|acute vision]] known among all vertebrates, with the exception of certain species of [[Bird of prey|predatory birds]].<ref>{{Cite journal |last=Caves |first=Eleanor M. |date=May 2018 |title=Visual Acuity and the Evolution of Signals |journal=Trends in Ecology & Evolution |volume=33 |issue=5 |pages=358–372 |doi=10.1016/j.tree.2018.03.001 |pmid=29609907 |bibcode=2018TEcoE..33..358C |url=https://www.cell.com/trends/ecology-evolution/fulltext/S0169-5347(18)30052-1 |access-date=29 July 2018}}</ref><ref>{{Citation |last1=Kirk |first1=E. Christopher |title=The Evolution of High Visual Acuity in the Anthropoidea |date=2004 |url=https://doi.org/10.1007/978-1-4419-8873-7_20 |work=Anthropoid Origins: New Visions |pages=539–602 |editor-last=Ross |editor-first=Callum F. |access-date=2023-07-30 |series=Developments in Primatology: Progress and Prospects |place=Boston, MA |publisher=Springer US |language=en |doi=10.1007/978-1-4419-8873-7_20 |isbn=978-1-4419-8873-7 |last2=Kay |first2=Richard F. |editor2-last=Kay |editor2-first=Richard F.}}</ref>

Primates have forward-facing eyes on the front of the skull; [[binocular vision]] allows accurate distance perception, useful for the [[Brachiation|brachiating]] ancestors of all great apes.<ref name="pough" /> A [[supraorbital ridge|bony ridge]] above the eye sockets reinforces weaker bones in the face, which are put under strain during chewing. [[Strepsirrhini|Strepsirrhines]] have a [[postorbital bar]], a bone around the eye socket, to protect their eyes; in contrast, the higher primates, [[Haplorhini|haplorhines]], have evolved fully enclosed sockets.<ref name="Campbell">{{cite book |author1=Campbell, B. G. |author2=Loy, J. D. |name-list-style=amp | year = 2000 | title = Humankind Emerging | publisher = Allyn & Bacon | pages = 85 |isbn=0-673-52364-0|edition=8th }}</ref>
[[File:PrimateFeet.jpg|thumb|right|upright|An 1893 drawing of the hands and feet of various primates]]
Primates show an evolutionary trend towards a reduced [[snout]].<ref name="palaeos">{{cite web |author1=White, T. |author2=Kazlev, A. |name-list-style=amp |url=http://www.palaeos.com/Vertebrates/Units/480Archonta/480.400.html#Primates | title=Archonta: Primates |publisher=[[Palaeos]]| access-date=2008-06-03 | date=2006-01-08 |archive-url=https://web.archive.org/web/20080512022901/http://www.palaeos.com/Vertebrates/Units/480Archonta/480.400.html <!--Added by H3llBot--> |archive-date=2008-05-12}}</ref> Technically, Old World monkeys are distinguished from New World monkeys by the structure of the nose, and from apes by the [[dentition|arrangement of their teeth]].<ref name="adw" /> In New World monkeys, the nostrils face sideways; in Old World monkeys, they face downwards.<ref name="adw" /> Dental pattern in primates vary considerably; although some have lost most of their [[incisor]]s, all retain at least one lower incisor.<ref name="adw" /> In most strepsirrhines, the lower incisors form a [[toothcomb]], which is used in grooming and sometimes foraging.<ref name="adw" /><ref name="EncycMammals" /> Old World monkeys have eight [[premolar]]s, compared with 12 in New World monkeys. The Old World species are divided into apes and monkeys depending on the number of [[Cusp (dentistry)|cusps]] on their [[Molar (tooth)|molars]]: monkeys have four, apes have five<ref name="adw" /> - although humans may have four or five.<ref>{{cite book |title=Wheeler's Dental Anatomy, Physiology, and Occlusion |last1=Ash |first1=M. M. |last2=Nelson |first2=S. J. |last3=Wheeler |first3=R. C. |publisher=W.B. Saunders |year=2003 |isbn=978-0-7216-9382-8 |page=[https://archive.org/details/dentalanatomyphy00majo/page/12 12] |url=https://archive.org/details/dentalanatomyphy00majo/page/12}}</ref> The main hominid molar cusp ([[hypocone]]) evolved in early primate history, while the cusp of the corresponding primitive lower molar (paraconid) was lost. Prosimians are distinguished by their immobilized upper lips, the moist tip of their noses and forward-facing lower front teeth.