Question

What are 2 unique characteristics of olfactory neurons in mammals?

Answer 1

Mammals (unlike other tetrapods) utilize a nose to sense volatile odors. The appearance of nasal turbinates and fossae, which resemble scroll-shaped spongy bones in the nasal passage, is one of the distinctive features of their evolution. These structures are paired on both sides of the midline nasal septum, linking the external nasal opening and the internal nasal aperture together. The first true mammals developed additional nasal tissue to carry more neurons that transfer olfactory information to the brain. Among amniotes, mammals were the first to evolve a complex system of nasal turbinates, which augment the surface area for olfactory epithelium.

Structural changes in rhinaria provide suggestive material for phylogenetic analysis. Generally speaking, the rhinarium is present in most species of mammals and is correlated with an acute sense of smell. Therefore, it is likely that this trait emerged in the protomammal stage. The adaptations that gave rise to this anatomical structure largely reflected the ecological factors that affected the mammals of the period. In most species with a rhinarium, the organ takes the form of a firm pad with dual nostrils, allowing for the processing of both olfactory and tactile information. The structure of the rhinarium is assumed to be important in the evolution of exploratory behaviour. A common assumption is that higher primates lost the rhinarium secondarily because of their decreasing reliance on olfaction.