Microsmatic primates: Reconsidering how and when size matters

Authors

  • Timothy D. Smith,

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    • School of Physical Therapy, Slippery Rock University, Slippery Rock, PA 16057
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    • Dr. Smith is an associate professor in the School of Physical Therapy, Slippery Rock University, and an adjunct research associate professor in the Department of Anthropology, University of Pittsburgh. A special emphasis in his research concerns evolution of the primate vomeronasal organ. Dr. Bhatnagar is a professor in the Department of Anatomical Sciences and Neurobiology, University of Louisville School of Medicine. He has studied chemosensory systems for more than 30 years and has studied the relative importance of olfaction versus vision in bats. Dr. Smith, Dr. Bhatnagar, and their colleagues have forthcoming articles in the The Anatomical Record, Part A, that discuss evolutionary aspects of the primate olfactory and vomeronasal systems. This work formed part of the basis for a presentation at the 73rd annual meeting of the American Association of Physical Anthropologists (April 2004) entitled “Is There a Valid Morphological Basis for Primate Macrosomia?”

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  • Kunwar P. Bhatnagar

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    • Dr. Smith is an associate professor in the School of Physical Therapy, Slippery Rock University, and an adjunct research associate professor in the Department of Anthropology, University of Pittsburgh. A special emphasis in his research concerns evolution of the primate vomeronasal organ. Dr. Bhatnagar is a professor in the Department of Anatomical Sciences and Neurobiology, University of Louisville School of Medicine. He has studied chemosensory systems for more than 30 years and has studied the relative importance of olfaction versus vision in bats. Dr. Smith, Dr. Bhatnagar, and their colleagues have forthcoming articles in the The Anatomical Record, Part A, that discuss evolutionary aspects of the primate olfactory and vomeronasal systems. This work formed part of the basis for a presentation at the 73rd annual meeting of the American Association of Physical Anthropologists (April 2004) entitled “Is There a Valid Morphological Basis for Primate Macrosomia?”


Abstract

The terms “microsmatic” and “macrosmatic” refer to species with lesser or greater levels, respectively, of olfactory function. Historically, primates are considered microsmats (olfactory sense reduced) with a concomitant increased emphasis on vision. The olfactory bulbs (forebrain centers that receive peripheral olfactory input) are proportionately smaller in primates compared to most other mammals. Similarly, the regions of the nasal cavity that are covered with olfactory epithelium (containing receptor cells) have proportionately less surface area in primates than other mammals. Thus, the generalization that primates are microsmatic is most frequently stated in terms of the proportional rather than absolute size of olfactory structures. Yet the importance of scaling to body size is unclear in regard to the chemical senses such as the olfactory or vomeronasal systems—do chemosensory structures such as olfactory bulbs and olfactory epithelium exhibit the same neural relationship to body mass that is seen for neural tissues that supply innervation to musculature or the skin? Previous studies examining neuronal density, volume, and/or surface area of the olfactory epithelium illustrate that different conclusions may be supported based on the parameter used. Plots of olfactory bulb volume versus body mass that generated for large-scale taxonomic studies or growth studies benefit from body mass (or total brain volume) with a comparative perspective. However, our examination of proportional versus absolute measurements implies that in comparisons within taxa, body size adjustments needlessly distort the data. As a final consideration, another embryonic derivative of the nasal placode, the vomeronasal organ, may warrant consideration regarding a definition of microsomia versus macrosomia. Anat Rec (Part B: New Anat) 279B:24–31, 2004. © 2004 Wiley-Liss, Inc.

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