Editing Oreopithecus (section)

===Positional behavior===
Its habitat appears to have been [[swamp]]y, and not [[savanna]] or [[forest]]. The postcranial anatomy of ''Oreopithecus'' features adaptations for suspensory arborealism. Functional traits related to suspensory locomotion include its broad thorax, short trunk, high [[intermembral index]], long and slender digits, and extensive mobility in virtually all joints. Its fingers and arms seem to show adaptations for climbing and swinging.

Its foot has been described as chimp-like, but is different from those of extant primates. The habitual line of leverage of the primate foot is parallel to the third [[metatarsal bone]]. In ''Oreopithecus'', the [[Anatomical terms of location#Left and right (lateral), and medial|lateral]] metatarsals are permanently [[Abduction (kinesiology)|abducted]] so that this line falls between the first and second metatarsals instead. Furthermore, the shape of the [[tarsus (skeleton)|tarsus]] indicate loads on the foot were transmitted to the medial side of the foot instead of the lateral, like in other primates.<ref name="Köhler-1997">{{harvnb|Köhler|Moyà-Solà|1997}}</ref> The metatarsals are short and straight, but have a lateral orientation increase. Its foot proportions are close to the unusual proportions of ''Gorilla'' and ''Homo'' but are distinct from those found in specialized climbers. The lack of predators and the limitation of space and resources in ''Oreopithecus''{{'}} insular environment favored a locomotor system optimized for low energy expenditure rather than speed and mobility.<ref name="Köhler-1997"/>

''Oreopithecus'' has been claimed to exhibit features that are adaptations to upright walking, such as the presence of a [[lumbar]] curve, in distinction to otherwise similar species known from the same period. Since the fossils have been dated to about 8 [[million years ago]], this would represent an unusually early appearance of upright posture.<ref name="Köhler-1997"/> However, a reevaluation of the spine from a skeleton of ''Oreopithecus'' has led to the conclusion that it lacked adaptations for habitual [[biped]]ality.<ref name="Ghose_2013">{{cite web |last=Ghose |first=Tia |title=Strange ancient ape walked on all fours |website=LiveScience.Com |publisher=TechMedia Network |date=2013-08-05 |url=http://www.livescience.com/38643-ancient-ape-walked-on-all-fours.html |access-date=2013-08-07 |df=dmy-all}}</ref><ref name="RussoShapiro2013">{{cite journal |last1=Russo |first1=G.A. |last2=Shapiro |first2=L.J. |title=Reevaluation of the lumbosacral region of ''Oreopithecus bambolii'' |journal=Journal of Human Evolution |date=2013-07-23 |df=dmy-all |doi=10.1016/j.jhevol.2013.05.004 |volume=65 |issue=3 |pages=253–265 |pmid=23891006|bibcode=2013JHumE..65..253R }}</ref>

====Semicircular canals====
The [[semicircular canal]]s of the inner ear serves as a sense organ for balance and controls the reflex for gaze stabilization. The inner ear has three canals on each side of the head, and each of the six canals encloses a membranous duct that forms an [[endolymph]]-filled circuit. Hair cells in the duct's [[auditory ampulla]] pick up endolymph disturbances caused by movement, which register as rotatory head movement. They respond to body sway of frequencies greater than 0.1&nbsp;Hz and trigger the vestibulocollic (neck) reflex and vestibuloocular (eye) reflex to recover balance and gaze stability. The bony semicircular canals allow estimates of duct arc length and orientation with respect to the sagittal plane.

Across species, the semicircular canals of agile animals have larger arcs than those of slower ones. For example, the rapid leaper ''[[Tarsius bancanus]]'' has semicircular canals much bigger than the slow-climbing ''[[Nycticebus coucang]]''. The semicircular canals of brachiating [[gibbon]]s are bigger than those of arboreal and terrestrial quadrupedal [[great ape]]s. As a rule of thumb, arc size of the ducts ''decreases'' with body mass and consequently slower angular head motions. Arc size ''increases'' with greater agility and thus more rapid head motions. Modern [[human]]s have bigger arcs on their anterior and posterior canals, which reflect greater angular motion along the sagittal plane. The lateral canal has a smaller arc size, corresponding to reduced head movement from side to side.
<ref name="Spoor-2003-p96">{{harvnb|Spoor|2003|pp=96–97}}</ref><!-- ref for para -->

[[Allometry|Allometric]] measurements on the [[bony labyrinth]] of BAC-208, a fragmentary cranium that preserves a complete, undeformed [[Petrous part of the temporal bone|petrosal bone]] suggest that ''Oreopithecus'' moved with agility comparable to extant [[great apes]]. Its anterior and lateral semicircular canal sizes fall within the range for great apes.
<ref name="Rook2004-p355">{{harvnb|Rook|Bondioli|Casali|Rossi|2004| p=355}}</ref>
Its relatively large posterior arc implies that ''Oreopithecus'' was more proficient at stabilizing angular head motion along the sagittal plane.