Scaling of mammalian ethmoid bones can predict olfactory organ size and performance

Abstract

The relation between size and performance is central for understanding the evolution of sensory systems, and much interest has been focused on mammalian eyes and ears. However, we know very little about olfactory organ size (OOS), as data for a representative set of mammals are lacking. Here, we present a cranial endocast method for estimating OOS by measuring an easily accessible part of the system, the perforated part of the ethmoid bone, through which the primary olfactory axons reach the olfactory bulb. In 16 species, for which relevant data are available, the area of the perforated ethmoid bone is directly proportional to the area of the olfactory epithelium. Thus, the ethmoid bone is a useful indicator enabling us to analyse 150 species, and describe the distribution of OOS within the class Mammalia. In the future, a method using skull material may be applied to fossil skulls. In relation to skull size, humans, apes and monkeys have small olfactory organs, while prosimians have OOSs typical for mammals of their size. Large ungulates have impressive olfactory organs. Relating anatomy to published thresholds, we find that sensitivity increases with increasing absolute organ size.

Aquatic adaptations in the nose of carnivorans: evidence from the turbinates

“…Our study confirms previous work demonstrating a reduction in olfactory organ size (defined in various ways) and presumed olfactory ability in semi-terrestrial and aquatic mammals, including some shrews (Sorex palustris; Larochelle & Baron, 1989), fissipeds (Ferron, 1973;Gittleman, 1991), pinnipeds, monotremes, and insectivores (Pihlströ m et al 2005;Pihlströ m, 2008). Some of these studies used osteological proxies for olfactory ability, including cribriform (ethmoid) plate area and olfactory bulb endocast size, and others estimated olfactory epithelial surface area from serial sections of whole heads.…”

“…Previous studies have shown that semiaquatic mammals tend to have smaller olfactory bulbs (Gittleman, 1991), reduced cribriform plates (the perforated bony ethmoid plate through which the nasal sensory neurons reach the olfactory bulb; Pihlströ m et al 2005), and diminished olfactory epithelial surface areas (Negus, 1958;Pihlströ m, 2008). This has been suggested to indicate reduced olfactory abilities because species known to have a well-developed sense of smell, such as dogs, have greater olfactory epithelial surface areas than those with a relatively poor sense of smell, such as humans and perhaps other Old World primates (Negus, 1958, Gilad et al 2004).…”

Unfolding the codes of short-term feed appetence in farm and companion animals. A comparative oronasal nutrient sensing biology review

“…The pig and the dog, among other non-primate mammals, have larger MOE surfaces and number of OSN than humans (Pihlstro¨m et al 2005) (Table 3). Furthermore, among the mammalians with known genomes, humans have fewest functional OR (Dryer 2000;Young and Trask 2002;Gilad et al 2004).…”

“…The number of pseudogenes may reflect a decrease in the animal's reliance on the sense of smell, likely due to increased reliance on other senses, such as Extrapolated from data corresponding to the wildboar (Sus escrofa) by Pihlstro¨m et al (2005). y Reviewed by Pihlstro¨m et al (2005).…”

Seasonal morphometry of the vomeronasal organ in the marsupial mouse, Antechinus subtropicus

“…Pihlström et al (2005) demonstrates a tendency for main olfactory organ size to be proportional to cribriform plate size in mammals, and that the larger absolute (not relative) size of the main olfactory organ, the higher olfactory sensitivity of that species. Bird et al (2014) likewise suggest that cribriform plate measures are closely correlated with main olfactory organ size.…”