Britten Sessions and Dr. Wilford Hess, Plant and Animal Life Sciences
Due to its implicit nature in species identification, hair has been studied and classified since the beginning of the 20th century. Hausman visualized enough hair characteristics and variation between mammalian species to attempt an identification system using light microscopy. His efforts in characterizing species based on hair patterns established the form by which other later mammalogists created taxonomy keys.
In creating dichotomous keys, past mammalogists indicated that immense effort would be required in order to gather the necessary data to elucidate differences and correctly identify a given species. Most modern keys are based on similar complex and time-consuming characteristics and analyses. Sessions et al, however, proposed a new method of mammalian identification using the hair cuticular layer alone with scanning electron microscopy which reduces the time necessary for identification.
Sessions et al5 demonstrated that taxonomy keys, although very complex in the past, could perhaps be simplified by comparing only the hair structure and size using a high resolution scanning electron microscope. Most other scientists in the past included not only the guard hair width, pattern, and size, but in addition, also included detailed data relating to the medulla, the color, and the physical properties of the hair along the entire hair shaft. In most instances, the complexity of these keys allow for careful and precise species identification. The method proposed by Sessions et al may not be the most precise method for exact species identification, but will allow for a quick identification. Their analysis, however, was limited to only 26 species.
In an effort to unify much of the research that has already taken place, the various classification techniques from the last thirty years were analyzed and compiled. In so doing, the resulting paper provides mammalogists with an up-to-date approach to species identification, key construction, and an understanding of the efficiency and approach to each method to species identification.
Five tables were constructed in the paper, displaying the differences in each technique, including a table on hair morphology classification techniques, epicuticle classification techniques, cortex/medulla classification techniques, cross section techniques, and the number of specimens studied and measuring techniques.
It was observed that most techniques could be separated into two categories: complex and simple. Although at first glance this division of hair classification may seem elementary and even rudimentary, it provides the basis for how the hair is treated and identified.
Most of the authors included in the analysis use the ‘complex’ method for mammalian identification. This method is labor intensive in that it requires the user to analyze several parameters before identifying the species, including an analysis of the hair prior to microscopy work, a complete analysis of the cuticle layer from the hair shaft to the tip, and for many keys, an analysis of the medulla layer as well. SEM improved the accuracy of this type of key, as indicated by Tupinier who demonstrated that SEM makes it possible to identify imbricate scales in many cases that had been classified as coronal scales using light microscopy. Problems associated with this type of classification include large amounts of time for precise identification and the money necessary to use a SEM. Benefits from this method include precise and correct identification.
A more simple approach was developed by Sessions et al wherein guard hair and underfur characteristics combined could be used to elucidate differences between orders and species. Although this simple approach may not be as accurate because the key is not based on multi-characteristics (medulla; cross section; entire guard hair cuticle layer characteristics), it provides a quick and easy approach to mammalian identification. Measurements are taken at the middle part of the hair (eliminates studying the entire length of the hair) and observed in at least a sample size of 30 hairs. Problems associated with this type of classification include a less precise method to mammalian identification and the cost associated with using a SEM. Benefits include a very quick and easy approach to a ballpark idea of identification.
Although the method proposed by Sessions et al9 does not seem to replace previous hair classification techniques, it does provide a new avenue and perspective to the common hair classification approach. Sessions et al9 further demonstrated in other subsequent studies the ability to classify hair based alone on hair width, scale length, pattern, and position in relation to the longitudinal direction of the hair (unpublished results).
A manuscript with the indicated results is currently being prepared for publication. Results leading up to this study have also been presented at six scientific conferences, including UCUR (Utah Conference for Undergraduate Research) and AAAS (American Association for the Advancement of Science).