The Shrinking Anthropoid Nose, the Human Vomeronasal Organ, and the Language of Anatomical Reduction

Abstract

Humans and most of our closest extant relatives, the anthropoids, are notable for their reduced "snout." The striking reduction in facial projection is only a superficial similarity. All anthropoids, including those with long faces (e.g., baboons), have lost numerous internal projections (turbinals) and spaces (recesses). In sum, this equates to the loss of certain regions of olfactory mucosa in anthropoids. In addition, an accessory olfactory organ, the vomeronasal organ, is non-functional or even absent in all catarrhine primates (humans, apes, monkeys). In this commentary, we revisit the concept of anatomical reductions as it pertains to the anthropoid nasal region. Certain nasal structures and spaces in anthropoids exhibit well-known attributes of other known vestiges, such as variability in form or number. The cupular recess (a vestige of the olfactory recess) and some rudimentary ethmoturbinals constitute reduced structures that presumably were fully functional in our ancestors. Humans and at least some apes retain a vestige that is bereft of chemosensory function (while in catarrhine monkeys it is completely absent). However, the function of the vomeronasal system also includes prenatal roles, which may be common to most or all mammals. Notably, neurons migrate to the brain along vomeronasal and terminal nerve axons during embryogenesis. The time-specific role of the VNO raises the possibility that our concept of functional reduction is too static. The vomeronasal system of humans and other catarrhine primates appears to qualify as a "chronological" vestige, one which fulfills part of its function during ontogeny, and then becomes lost or vestigial.

The ethmoidal region of the skull of <i>Ptilocercus lowii</i> (Ptilocercidae, Scandentia, Mammalia) – a contribution to the reconstruction of the cranial morphotype of primates

“…In contrast Tupaia species are mainly diurnal, most of which forage on the ground and in bushes and thus stereoscopic vision might be less important (Hofer, 1957;Cartmill, 1972;Sargis, 2001). Though Scandentia have relatively large eyes the posterior ethmoidal region is not reduced (see Smith et al, 2014b). Our new findings on the investigated Scandentia support earlier observations on Tupaia that the nasal cavity of Scandentia is well-developed and clearly indicates macrosmatic sense, the ability of high olfactory performance (Spatz, 1964;Zeller, 1987;Smith et al, 2014b).…”

“…Though Scandentia have relatively large eyes the posterior ethmoidal region is not reduced (see Smith et al, 2014b). Our new findings on the investigated Scandentia support earlier observations on Tupaia that the nasal cavity of Scandentia is well-developed and clearly indicates macrosmatic sense, the ability of high olfactory performance (Spatz, 1964;Zeller, 1987;Smith et al, 2014b). Macrosmatic ability is a plesiomorphic mammalian character (see Maier and Ruf, 2014), and many of the here described characters and ontogenetic transformations are correlated with this feature and represent plesiomorphic states for the clade Scan-dentia (Zeller, 1986b(Zeller, , 1987Maier and Ruf, 2014;Ruf, 2004Ruf, , 2014.…”

“…Thus, not only is olfaction less important in haplorhine primates but also the enlarged eyes and rostrally oriented orbits are conflicting with the posterior nasal capsule in terms of the demand for space (Maier, 1983;Maier and Ruf, 2014). However, Scandentia have an elaborated ethmoidal region with well-developed olfactory turbinals which is obviously not in spatial conflict with the enlarged eyes (Smith et al, 2014b). As skull size, chewing apparatus, basicranial kyphosis, and proportion of the brain cavity are comparable in Ptilocercus and Tupaia, these factors obviously do not influence the morphology of the anterior basicranium, i.e.…”

The loss of scents: Do defects in olfactory sensory neuron development underlie human disease?

“…Support for the diminished olfaction in cetaceans include genetic changes observed across the whales species, correlating with the structural changes: approximately 29–58% of the olfactory receptors in baleen whales are pseudogenes, compared to 74–100% in the toothed whales (Kishida et al, ). Finally, like humans, apes, and monkeys, where the vomeronasal organ is non‐functional or absent (Smith et al, ), the vomeronasal organ is also absent in the extant cetaceans (Buhl and Oelschlager, ; Oelschlager et al, ). The loss of the VNO has implications for interpretations of neuroendocrine defects in humans (discussed below).…”

La Sagrada Familia of the Human Body: The Anatomical Record Continues Our Exploration of the Unique World of the Cranial Nerves in Volume 2 of Our Special Issue, Cranial Nerves: Morphology and Clinical Significance

“…A constant, however, was the plethora of fine studies that appeared in The Anatomical Record . These include: Lin et al’s () study of pathways communicating with the pterygopalatine ganglion in the cat; Plenat et al's () examination of the intra and juxtavagal paraganglia in humans; Mu and Sanders' () insightful study on the hypoglossal nerve and neuromuscular organization of the tongue in canids; the study by Henry et al () on trigeminal distribution and function in the extraordinary, naked mole rat; George and Holliday's () biting study illuminating alligator trigeminal nerve facial sensation (recommended reading for anyone thinking of moving to Florida); Diaz et al's () insightful overview of the parts of the olfactory system sensu lato ; a thought‐provoking paper by Smith et al () on the vomeronasal organ and its involvement with the olfactory nerve in nonhuman primates (Tim Smith, of Slippery Rock University in Pennsylvania, is recognized as one of the brightest and most creative thinkers in evolutionary morphology today and, fortunately for The Anatomical Record , is also our Associate Editor); and (Boehm and Kondrashov's () insightful study on the distribution of neuron cell bodies in the intraspinal portion of the spinal accessory nerve, to mention but a few.…”