Editing Kenyanthropus (section)

== Anatomy ==
{{Multiple image|direction=vertical|align=left|image1=Kenyanthropus platyops IMG 2945-white.jpg|image2=Kenyanthropus platyops IMG 2946-white.jpg|footer=KNM-WT 40000 from different angles}}
KNM-WT 40000 has been heavily distorted during the fossilisation process, the braincase shifted downwards and backwards, the nasal region to the right, and the mouth and cheek region forward. It is unclear if the specimen represents a male or a female.<ref name=":0"/>

''Kenyanthropus'' has a relatively flat face, including subnasally, between the nose and the mouth (the nasoalveolar clivus). The clivus inclines at 45° (there is relaxed sub-nasal [[prognathism]]), steeper than almost all other australopithecine specimens (on the upper end of variation for ''Paranthropus''), more comparable to ''H. rudolfensis'' and ''[[Homo habilis|H. habilis]]''. This is the earliest example of a flat face in the hominin fossil record. Unlike ''A. afarensis'', ''Kenyanthropus'' lacks the anterior pillars, bony columns running down from the nasal aperture (nose hole). It is also one of the longest early hominin clivi discovered at {{cvt|32|mm}}. The nasal aperture (nose hole) is narrow compared to that of ''Australopithecus'' and ''Paranthropus''. The cheekbones are tall and steep, and the [[anatomical terms of location#Anterior and posterior|anterior]] surface (where the cheeks juts out the most) is positioned above the premolars, more frequently seen in ''Paranthropus'' than other hominins. The zygomaticoalveolar crest (stretching between the cheek and the teeth) is low and curved. Overall, the face resembles ''H. rudolfensis'', though has longer nasal bones, a narrower nasal aperture, a shorter postcanine (the [[molar (tooth)|molars]] and [[premolar]]s) tooth row, and a less steeply inclined (less flat, more prognathic) midfacial region. Much later ''Paranthropus'' are also characterised by relatively flat faces, but this is generally considered to be an adaptation to maximise bite force through enormous teeth, which ''Kenyanthropus'' enigmatically does not have.<ref name=":0"/>

Among all the specimens, only the M<sup>2</sup> (2nd upper left molar) and the [[dental alveolus|tooth sockets]] of the left side of the mouth of KNM-WT 40000 are preserved well enough to measure and study. With dimensions of {{cvt|11.4x12.4|mm2}}, a surface area of {{cvt|141.4|mm}}, it is the smallest M<sup>2</sup> ever discovered for an early hominin. For comparison, those of ''A. afarensis'' in the comparative sample Leakey and colleagues used ranged from about {{cvt|160|to|225|mm2}}, ''H. habilis'' and ''H. rudolfensis'' {{cvt|165|to|250|mm2}}, and the robust ''P. boisei'' (with the largest molars among hominins) about {{cvt|240|to|380|mm2}}. The reconstructed dimensions of KNM-WT 38350's M<sup>1</sup> are {{cvt|10.5x12|mm}} for a surface area of {{cvt|126|mm2}}, which is on the lower end of variation for ''A. anamensis'', ''A. afarensis'' and ''H. habilis''. The thick molar [[tooth enamel|enamel]] is on par with that of ''A. anamensis'' and ''A. afarensis''. KNM-WT40000 retains the ancestral ape premolar [[tooth root]] morphology, with a single lingual [[tooth root|root]] (on the tongue side) and two buccal roots (towards the cheeks), though the P<sup>4</sup> of KNM-WT 38350 may only have a single buccal root; the ancestral pattern is frequent in ''Paranthropus'' and variable in ''Australopithecus''. Individuals of more derived species typically have single-rooted premolars. The canine jugum is not visible (a line of bone in the maxilla corresponding to the canine tooth root), which may mean the canines were not that large. The cross-sectional area of the I<sup>2</sup> (2nd upper [[incisor]]) is 90% the size of that of I<sup>1</sup>, whereas it is usually 50 to 70% in other great apes. The tooth roots of the incisors do not appear to be orientated out (there was probably no alveolar prognathism, the front teeth did not jut forward).<ref name=":0"/>

Brain volume is uncalculable due to distortion of the braincase, but it was probably similar to that of ''Australopithecus'' and ''Paranthropus''.<ref name=":0"/> A sample of five ''A. afarensis'' averaged 445 cc.<ref>{{cite journal|first1=P.|last1=Gunz|first2=S.|last2=Neubauer|first3=D.|last3=Falk|display-authors=et al.|year=2020|title=''Australopithecus afarensis'' endocasts suggest ape-like brain organization and prolonged brain growth|journal=Science Advances|volume=6|issue=14|page=eaaz4729|doi=10.1126/sciadv.aaz4729|pmid=32270044|pmc=7112758|bibcode=2020SciA....6.4729G|doi-access=free}}</ref> Like ''Paranthropus'', there is no frontal trigon (a triangle formed by the conjunction of the [[temporal line]]s behind the brow ridge). Unlike ''H. habilis'' but like ''H. rudolfensis'', there is no [[sulcus (morphology)|sulcus]] (trench) behind the brow ridge. The degree of [[postorbital constriction]], the narrowing of the braincase in the [[frontal lobe]] region, is on par with that of ''Australopithecus'', ''H. rudolfensis'', and ''H. habilis'', but less than ''[[Paranthropus boisei|P. boisei]]''. Like the earlier ''[[Australopithecus anamensis|A. anamensis]]'' and ''[[Ardipithecus ramidus|Ar. ramidus]]'', the [[tympanic bone]] retains the ancestral hominin ear morphology, lacking the [[petrous part of the temporal bone|petrous crest]], and bearing a narrow [[ear canal]] with a small opening. The [[foramen magnum]], where the skull connects to the [[vertebral column|spine]], was probably oval shaped as opposed to the heart-shaped one of ''P. boisei''.<ref name=":0"/>