A Microscopical Study of Exotic Animal Hairs: Part 2

Brookfield Zoo, Brookfield, Illinois, has been exceptionally cooperative and generous with the collection of hairs from an array of animals at their zoo.  Several samples were examined and “A Microscopical Study Of Exotic Animal Hairs: Part 1” was just the beginning of what could become lifelong work. Working with the Zoo has enabled McCrone Associates to begin setting an exhibit in the Hamill Family Play Zoo, located within the Zoo, to teach guests how hairs appear when viewed through a microscope. This, hopefully, will allow younger generations to begin to appreciate the capabilities of the microscope. The exhibit will be interactive, displaying a flip-book picturing reference samples, set next to microscopes used to view the samples. The collection of hairs provided has made it possible for McCrone Associates to take transmitted-light photomicrographs using plane-polarized light, fully-crossed polarizers, and scanning electron micrographs (SEMs), and make scale castings of the actual hairs.

In this follow-up to “A Microscopical Study Of Exotic Animal Hairs: Part 1”, the animals have been chosen at random. The Brown Bear, Western Lowland Gorilla, and African Wild Dog are all on the endangered species list. The Zoo is an active participant in the Species Survival Plan (SSP) for both the Western Lowland Gorilla and the African Wild Dog. The California Sea Lion, due to its protection by the Marine Mammal Protection Act of 1972, is not considered endangered. The Aardwolf is currently classified as rare. 

Brown Bear (Ursus arctos)

Ursus arctos, commonly known as the Brown Bear, is found on three continents, making it the most widespread bear species on Earth. Although its range is wide, its population numbers are still low. Brown Bears have been hunted, and their habitats have been overtaken by human expansion, which may explain why they are on the endangered species list. Their body color is usually dark brown, but can range in shades from a cream-color to almost black. Some of their hairs may be tipped with a whitish-silver color giving their coat a sheen-like appearance.

In Meltmount™ 1.662, you will notice a continuous medulla in both transmitted light and with fully-crossed polarizers. This sample has a stellate appearance, finger-like projections radiating out into the cortex; this type is often found in the tail hairs of larger mammals. Figures 1 and 2 are X300 photomicrographs of Brown Bear hair (both polarizer and analyzer have been rotated 45°).

Notice the moderately high birefringence using fully-crossed polarizers (Figure 2). You can just begin to make out the scale pattern along the edge of the hair in the transmitted light photomicrograph (Figure 1). The photomicrograph of the cross-section, Figure 3, shows a circular-to-oval shape with a transparent medulla due to the stellate appearance. The medullary index was calculated to be 0.14.

Scale casts were made of the hairs using clear nail polish in order to provide optimum study preparation of the scale pattern. The contrast and definition are both greatly improved (Figure 4); the irregular mosaic scale pattern is now easily visible. Images were captured at X1200, 10 kV, using a scanning electron microscope (SEM), to show more topographical detail which is visible at this higher magnification. This sample is ~64 µm wide, and has 8-12 scales per 100 µm. The margins appear to be relatively smooth and near to one another (Figure 5).

Gorilla (Gorilla gorilla gorilla)

Next, hair from Gorilla gorilla gorilla, otherwise known as the Western Lowland Gorilla was analyzed. Gorillas are great apes, along with orangutans, chimpanzees, and bonobos. There are three subgroups of gorilla: the Eastern Lowland Gorilla, the Mountain Gorilla, and the Western Lowland Gorilla. The Western Lowland Gorilla is slightly smaller and lighter in color that the other two groups. Western Lowland Gorillas have brownish-gray highlights among their black fur. The silverback is the only fully adult male in a troop, and, as his name suggests, he possesses a broad strip of silver fur across his back. They reside farther west in Africa than any other gorillas, and are currently on the endangered species list. There is also a SSP on behalf of the Western Lowland Gorilla.

In Meltmount™ 1.662, notice the wide continuous medulla in both transmitted light and fully-crossed polarizers; both images were taken at X300 (Figure 6 & 7). With the polarizers crossed, the gorilla hair shows relatively high birefringence (Figure 7).

The cross-section shows a circular shape with a medium-to-wide medulla. The sections that have a darker/black appearance indicate pigment granules. The medullary index was calculated to be 0.25 (Figure 8).

The scale cast of this sample shows a prominent, irregular wave pattern; the margins appear to be near, with rippled edges (Figure 9). The SEM image, taken at X500, 5 kV, shows this sample to be ~120 µm wide and have 10-15 scales per 100 µm (Figure 10). Notice what appears to be a damaged area towards the bottom of the image.  This scratched appearance may be due to all of the extensive grooming activity that gorillas undergo.

African Wild Dog (Lycaon pictus)

Lycaon pictus, otherwise known as the African Wild Dog, are medium-sized dogs that live on the savannah and open woodlands of central and southern Africa. They have a very distinctively patterned fur coat, no two are exactly alike. Their colorful coats can range from any combination of black, yellow, white, and dark brown. They possess a 12-16” long tail with a bushy white tip. The African Wild Dog is currently on the endangered species list and has a SSP working in its favor.

In Meltmount™ 1.662 you will notice a narrow, continuous medulla, and a low birefringence when the polarizers are fully crossed. Both images were taken at X300 (Figure 11 & 12).

The cross-section shows a circular shape with a medium-to-wide medulla.  Pigmentation is also present in these samples. The medullary index was calculated to be 0.47 (Figure 13).

A scale cast was made, and it shows an irregular mosaic pattern (Figure 14). The SEM image, taken at X900, 5 kV, shows this sample to be ~ 70 µm in width, with 12-16 scales per 100 µm; the margins are near with smooth-crenate edges (Figure 15).

California Sea Lion (Zalophus californianus)

For a marine mammal species, we have Zalophus californianus. They, along with seals and walruses, belong to a “fin-footed” group called pinnipeds. They can be found anywhere along the Pacific coast of North America, from Vancouver, Canada to Baja, Mexico. They sometimes gather in large masses to hunt for fish, such as off the coast of San Francisco where some consider them a nuisance. They are usually brownish-gray to silver in color with a thick coat of short fur and a heavy layer of fat under their skin to keep them warm in cold water.  Their bodies are smooth and streamlined which enables them to swim with little resistance. Once at very dangerously low populations, the California Sea Lion, and all other marine mammals, are now protected by the MMPA (Marine Mammal Protection Act) of 1972.

In Meltmount™ 1.662, notice the unusual continuous globular medulla, with no visible scale pattern; in crossed polarized light there is low birefringence seen (Figure 16 & 17).

The cross-section shows the hair to be a cigar shape with a narrow medulla.  Some pigmentation can be seen. The medullary index was calculated to be 0.32 (Figure 18).

A scale cast was made to determine the scale pattern; the cast shows a distinct, irregular wave pattern, with margins that are near with crenate edges (Figure 19). The SEM image, take at X600, 5 kV, was difficult to capture; the first attempt was unsuccessful because of the absence of a scale pattern. Finding this to be extremely unusual, a second attempt was made with the hairs turned over. The loss of the scale pattern on the exposed side of the hair (first attempt) is due, possibly, to streamlining in the water. The underside, or protected side (second attempt), revealed that there are 16-20 scales per 100 µm and that this sample is ~150 µm in width (Figure 20). The angle at which this image was captured shows the loss of scales occurring toward the top of the image.

Aardwolf (Proteles cristatus)

Not related to the Aardvark, Proteles cristatus, or the Aardwolf, is actually a relative of the hyena family. Aardwolf is Afrikaans for “earth wolf.” The Aardwolf is found mainly in the open, sandy plains or bush country of eastern and southern Africa.  Standing a mere 15-20” in height, the aardwolf possesses long loose under fur which is mixed with larger coarser guard hairs. They have a defense mechanism which enables them to erect the hair of the mane to appear twice their normal size to defend against predators. Their body hair is usually yellow-gray with black stripes. Their legs are banded black with entirely-black paws. They have a bushy, black-tipped tail.  The Aardwolf is not on the endangered species list, but is classified as rare in South Africa due to human hunting and habitat destruction.

At X300 in Meltmount™ 1.662 you will notice a very broad continuous medulla and moderately high birefringence using crossed polarized light (Figure 21 & 22).

The cross-section shows the hairs to be oval-to-kidney shape. The medulla appears to be wide; the medullary index was calculated to be 0.62 (Figure 23).

The scale cast of this sample shows an irregular wave-mosaic pattern. The SEM image of this sample, taken at X400, 5 kV, shows the margins are near with crenate edges. The width of the sample is ~163 µm, and there are 10-15 scales per 100 µm (Figure 24 & 25).

Among the observations of the animal hairs described above, morphological differences are apparent from species to species. It should be noted that the medulla may change within the length of the hair, and/or within different hairs on the body, as in the stellate appearance in the Brown Bear.  The scale pattern may also differ, depending on environmental conditions, as seen on the California Sea Lion hair, and possibly the Western Lowland Gorilla hair.


Once again the cooperation of Brookfield Zoo, Brookfield, IL, in the collection of the animal hair samples used in this study is acknowledged and greatly appreciated.  Thank you to Brian J. Bierman, McCrone Associates, for his assistance in capturing the SEM images.


Bisbing, R. E. (1982).  The Forensic Identification and Association of Human Hair. Forensic Science Handbook  (Saferstein, R.; ed.).  Prentice Hall, Englewood Cliffs.

Brunner, Hans, and Brian Coman (1974)The Identification of Mammalian Hair.  Inkata Press, Melbourne.

Hicks, John W. (1977).  Microscopy of Hair–A Practical Guide and Manual, FBI Laboratory Technical Supplement. Washington, D.C.

Moore, Tommy D., Liter E. Spencer, and Charles E. Dugnoll, (1974).  Identification Of the Dorsal Guard Hairs of Some Mammals of Wyoming. Wyoming Game and Fish Department. Cheyenne, Wyoming.

Brookfield Zoo Web Site: http://www.brookfieldzoo.org.

P & G Beauty Science: http://www.pantene.com/haircare/hair_twh_12.htm.

Crime Library: http://www.crimelibrary.com

Hair Analysis: http://www.bergen.org

Phoenix Zoo: http://www.phoenixzoo.org

Brown Bear:  http://www.bearbiology.com

Carnivora:  http://www.press.jhu.edu



The brown bear stellate medulla is due to keratinophilic fungi (KLF)invading the shaft and tunnelling their way along the medulla as this is not as dense as going through the dense cortex. This stellate medulla is seen in polar bears (Zoo specimens) as they spend long bouts of lying on the ground thereby allowing KLF access to their hairs. Stellate medulla is also seen in wombats (subterrainean dwellers) and in woolly mammoth and woolly rhino hair due to being entombed in soil. The transparent medulla is not due to the stellate medulla per se, it is due to the medullary structures be being consumed by KLF.

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