Rhinarium

The rhinarium is present in mammals such as the cat.

Howler monkeys are examples of haplorrhines, which have simple nostrils and a dry upper lip instead of a wet rhinarium.

Dogs have rhinarium as well.

The rhinarium is the wet, naked surface around the nostrils of the nose in most mammals. Colloquially it is called a "wet snout" or "wet nose".

Mammals with rhinariums tend to have a stronger sense of olfaction, and the loss of the rhinarium in the haplorrhine primates is related to their decreased reliance on olfaction, being associated with other derived characteristics such as a reduced number of turbinates. The rhinarium is very useful to animals with good sense of smell because it acts as a wind direction detector. The cold receptors in the skin respond to the place where evaporation is the highest. Thus the detection of a particular smell is associated with the direction it came from.^[1]

Primates are phylogenetically divided into Strepsirrhini ("curly-nosed" primates with rhinariums, which is the ancestral condition) and Haplorrhini ("simple-nosed" primates which have replaced the rhinarium with a more mobile, continuous, dry upper lip).

Note that the traditional paraphyletic "prosimian" division of primates cannot be characterised by the presence of a rhinarium, due to its absence in the tarsiers, and loss of the rhinarium is not a synapomorphy of the simians or anthropoids, but a symplesiomorphy shared with the tarsier outgroup.

References

• Fleagle, J. G. (1988). Primate adaptation and evolution. San Diego: Academic Press. 

1. ^ Dijkgraaf S.;Vergelijkende dierfysiologie;Bohn, Scheltema en Holkema, 1978, ISBN 90 313 0322 4