Editing Howler monkey (section)

==Anatomy and physiology==
[[File:Allouataadulto 500px.jpg|thumb|upright|left|Male [[mantled howler]]]]

Howler monkeys have short snouts and wide-set, round nostrils. Their noses are very keen, and they can smell out food (primarily fruit and nuts)  up to 2&nbsp;km away. Their noses are usually roundish snout-type, and the nostrils have many sensory hairs growing from the interior. They range in size from {{convert|56|to|92|cm|in|abbr=on}}, excluding their tails, which can be equally long; in fact in some cases the tail has been found to be almost five times the body length.{{citation needed|date=September 2020}} This is a prime characteristic. Like many New World monkeys, they have [[prehensile tail]]s, which they use while picking fruit and nuts from trees. Unlike other [[New World monkey#Characteristics|New World monkey]]s, both male and female howler monkeys have [[trichromat]]ic color vision.<ref>{{cite journal|last=Jacobs|first=G. H.|author2=Neitz, M. |author3=Deegan, J. F. |author4=Neitz, J. |year=1996|title=Trichromatic colour vision in New World monkeys|journal=[[Nature (journal)|Nature]]|issue= 6587|pages=156–158|doi=10.1038/382156a0|volume=382|pmid=8700203|bibcode=1996Natur.382..156J |s2cid=4305822 }}</ref> This has [[Evolution of color vision in primates|evolved independently]] from other New World monkeys due to [[gene duplication]].<ref name=Lucas2003>{{cite journal |author1=Lucas, P. W. |author2=N. J. Dominy | year = 2003 | title = Evolution and function of routine trichromatic vision in primates | journal = Evolution | volume = 57 |pages = 2636–43 | pmid = 14686538 | issue = 11 | doi=10.1554/03-168}}</ref> They have lifespans of 15 to 20 years. Howler species are dimorphic and can also be dichromatic (i.e. ''Alouatta caraya''). Males are typically 1.5 to 2.0&nbsp;kg heavier than females.

[[File:Alouatta seniculus 5perspective.jpg|thumb|upright=0.8|Skull]]

Males experience an evolutionary trade off between investments in [[Sexual selection in mammals|precopulatory]] traits, larger [[hyoid bone|hyoids]] but smaller [[testes]], or [[Copulation (zoology)|post-copulatory]] traits, larger testes and smaller hyoids. The hyoid of ''Alouatta'' is [[Skeletal pneumaticity|pneumatized]], one of the few cases of postcranial pneumaticity outside the [[Saurischia]]. The volume of the hyoid of male howler monkeys is negatively correlated with the dimensions of their testes, and with the number of males per group. Larger hyoids decrease space between [[formant]], and offers impression of larger body size.<ref name=":1">{{Cite journal |last1=Dunn |first1=Jacob C. |last2=Halenar |first2=Lauren B. |last3=Davies |first3=Thomas G. |last4=Cristobal-Azkarate |first4=Jurgi |last5=Reby |first5=David |last6=Sykes |first6=Dan |last7=Dengg |first7=Sabine |last8=Fitch |first8=W. Tecumseh |last9=Knapp |first9=Leslie A. |date=2015-11-02 |title=Evolutionary Trade-Off between Vocal Tract and Testes Dimensions in Howler Monkeys |journal=Current Biology |language=en |volume=25 |issue=21 |pages=2839–2844 |doi=10.1016/j.cub.2015.09.029 |pmid=26592343 |pmc=4635310 |bibcode=2015CBio...25.2839D |issn=0960-9822}}</ref> They have a flat cranial shape due to a folivorous diet and an advanced vocal system. Their brain growth is posterior  rather than superior or inferior as in other platyrrhines.<ref>{{Cite journal |last1=Fiorenza |first1=Luca |last2=Bruner |first2=Emiliano |title=Cranial shape variation in adult howler monkeys(Alouatta seniculus) |url=https://onlinelibrary.wiley.com/doi/epdf/10.1002/ajp.22729 |journal=American Journal of Primatology |year=2018 |volume=80 |issue=1|pages=e22729 |doi=10.1002/ajp.22729 |pmid=29206291 |s2cid=29382338 |url-access=subscription }}</ref>

===Locomotion===
Howler monkeys generally move quadrupedally on the tops of branches, usually grasping a branch with at least two hands or one hand and the tail at all times. Their strong prehensile tails are able to support their entire body weight. Fully grown adult howler monkeys do not often rely on their tails for full-body support, but juveniles do so more frequently. A significant amount of their travel  is done through the ground, with sitting and resting being their most frequent postures.<ref>{{Cite journal |last=Ybarra |first=Miguel A. Schön |date=1984 |title=Locomotion and postures of red howlers in a deciduous forest-savanna interface |url=https://onlinelibrary.wiley.com/doi/abs/10.1002/ajpa.1330630109 |journal=American Journal of Physical Anthropology |volume=63 |issue=1 |pages=65–76|doi=10.1002/ajpa.1330630109 |pmid=6703035 |url-access=subscription }}</ref>