Mammal Specimen Preparation

Statement of Purpose

These links and documents contain information about mammalogy specimen preparation.

Contributors

Andrea M. Carrillo

Introduction

Mammal specimens are prepared in multiple formats depending on anticipated collection needs and utility.

Study skins and skulls are the standard method of preparation in Mammalogy Collections, though complete skeletons, fluid-preparations, and other preparation methods are also commonplace. Non-skin preparations represent a growing proportion of collections as emerging museum technologies facilitate discovery (e.g., CT scanning, 3D photogrammetry, high resolution focus stacking).¹ Additionally, tissues and symbionts are often collected at the time of preparation.

Study Skin Preparation

Study skins capture the outward appearance of an individual, preserving anatomical structures and plumage. Mammal skins are prepared in a standard pose in order to provide a basic unit of comparison as well as to minimize storage footprint. Large, long-tailed species, or primates might have slight variations on the classic cylindrical study skin shape, such as curved tails and legs, or folded skins to consolidate fragile extremities.

Historically, study skin preparation follows Hall (1962), with slight variations in method unique to individual preparators or institutional needs. Liberal application of chemical pesticides such as arsenic or mercuric chloride on the inside of skins to deter protein-feeding pests has largely been eradicated due to human health² and specimen conservation risks, and improvements in collections storage systems. Generally, no chemicals are employed in the preparation process save for occasional use of a mild detergent to remove oils or blood from the skin. At times, 10% buffered formalin is utilized to ensure fleshy parts of the body do not rot on study skins. Often a non-chemical absorbent is used in lieu of washing, such as corncob dust, cornmeal, or sawdust. However, preparators in tropical field conditions may opt for a desiccant such as Borax to discourage rot, though the long-term consequences of Borax on preserved study skins are unknown.

Skin preparation follows these general steps (see Preparation Procedure Resources below for links to detailed study skin preparation guides):

• Data gathering – measurements, weight and various external attributes are recorded prior to skinning. Specimens may also be examined for ectoparasites at this stage.
• Skinning – An incision is made at the abdomen from the base of the ribs to the line of the knees. The skin is worked away from the carcass, cutting at the knees and wrist to extract the body and retain the extremities. Larger study skins may require an additional incision down the length of the tail or limbs. Depending on the institution, one side of the limbs may be removed to stay whole with the skeleton.
• Tissue collection – Tissues are typically taken after the skinning stage. Detected internal parasites may be harvested if desired. Internal data attributes are documented as they are encountered, such as fat deposition, gonad measurements, and placental scars.
• Cleaning – The skin is cleaned of residual tissue, organs, blood, fat and oils. Especially fatty mammals may require use of a scraping tool or fleshing wheel in addition to standard dissection instruments to fully strip grease from the skin. Washing or using an absorbent are typically employed at this stage. Wet skins are dried with forced cold air and/or tumbled in absorbent.
• Stuffing – The mouth is often sewed before stuffing but can be left unsewed for smaller specimens. The skin is stuffed with cotton, polyester batting, or excelsior/wood wool by shaping the stuffing to the size of the removed carcass. A wire is inserted into the limbs.  Cotton is then inserted in the limbs to replace the muscle removed during skinning. Wire wrapped in cotton is inserted into the tail.
  • Stuffing skins using excelsior: Unlike stuffing with cotton or polyester batting, stuffing with excelsior is not widely written about in preparation manuals. Stuffing larger skins with excelsior provides a strong structure made of natural, ph neutral materials. A step-by-step guide on stuffing mammals with excelsior is as follows:
    • Use excelsior and 100% cotton twine to wrap a strong core of hay the length of the specimen from the tip of the nose to about the knees.
    • Start building the shape of the head by slowly adding excelsior with twine to the dimensions of the removed skull.
    • Continue to build the shape of the body with more excelsior and twine. Keeping in mind to not make the body too tall or too long. Continually check the size and shape by periodically inserting the formed body into the clean and dry skin.
    • Optional: wrap the finished formed body with a layer of cotton for a smoother finish.
    • Insert the form as you would a cotton or polyester body.
    • Add cotton to the tip of the nose and eyes via the mouth or eye openings.
• Drying – All incisions and holes are sewed, typically using a baseball stitch. The fur is smoothed and completely dried, and the skin is pinned belly down on a board. Pins are typically placed in through the forefeet, hindfeet, and across the tail. Some taxa, such as bats, may require more pins. Forefeet are not to go past the tip of the nose. Specimens should dry for at least 2 weeks or longer, depending on the size.

Skin Patch Preparation

Skin patches are an inexpensive and time efficient way to preserve sections of chemical-free skin. This mode of preparation is typically done on larger specimens when a study skin would be impractical to store. They are usually accompanied by a skeleton or a partial skin. Unlike tanned skins, skin patches allow users to analyze sections of skin that have not been chemically processed.

Skin patch preparation procedures follow these general steps:

• Data gathering – (as above)
• Patch removal – a section of skin is located and selected. The skin is cut into a square patch of the desired location and size.
• Cleaning – (as above)
• Drying – Wet skin patches are dried with forced cold air and/or tumbled in absorbent. Once dry, the skin can be sewn tightly onto wire grates or panels that allow for maximum airflow. Thicker skins may require specialized leather working S-curved needles, waxed thread, awls and/or cheese cloth to keep the skin tightly sewn to the wire grate.

Skeleton Preparation

Mammal skeleton preparation generally follows the study skin methods outlined above, though no bones are cut during processing to preserve the integrity of the resulting osteological specimen. Bones are cleaned using Dermestid hide beetles, maceration, or burial. Other methods such as boiling are not an accepted museum technique.

Following defleshing, bones may be treated with ammonia, detergents, enzymes, hydrogen peroxide, or ethanol to degrease, bleach, or surface clean elements. Some institutions discourage application of chemicals due to the unknown long-term conservation effects on specimens. However, solvents are widely used on greasy specimens and often considered necessary to draw out fatty marrow that can lead to data dissociation through leaching onto data tags or by making bones difficult to number.

• See Preparation Procedure Resource section and Skeleton Preparation page for step-by-step skeleton preparation procedures.

Fluid-specimen Preparation

Pickling preserves the whole organism and allows for future examination of internal structures. Mammal specimens may be fixed in 10% buffered formalin before preservation in 70% ethanol. Mammal fluid specimen preparation follows these general steps:

• Data gathering – (see above)
• Tissue collection – Fixation disrupts protein chain structure and renders tissues unsuitable for DNA extraction, therefore tissues must be collected prior to fixation.
• Fixation – Carcasses are injected with 10% buffered formalin minimally in the thoracic, abdominal and cranial regions, as well as in major muscle groups for large taxa to ensure adequate fixative penetration of dense internal structures. Specimens are then placed in a formalin bath. Fixation time is dependent on specimen size and must allow for complete arrest of post-mortem changes in tissues yet avoid decalcification of the skeleton through prolonged soaking.³ Specimens should be removed from the bath once firm to the touch and no longer soft-bodied.
• Ethanol laddering – Fixed specimens are rinsed with fresh water and transitioned to ethanol in gradually increasing concentrations. Stepping up ethanol concentration using the ladder method prevents osmotic shock as the specimens are transitioned from a water-based fixative to a comparatively dehydrated ethanol solution.
  • Buffered Formalin Recipe (per 1 liter of solution):
• 9 parts distilled or deionized water
• 1 part 37% formaldehyde
• 4g monobasic sodium phosphate (NaH₂PO₄H₂O)
• 6.5g dibasic sodium phosphate anhydrate (Na₃HPO₄)

Other Forms of Preparation

There are countless other forms of preservation and preparation that have not been covered in this guide or in text. Each will have their own uses and needs for preservation. The general guidelines above and in the resources section provide some general steps on where to start.

Preparation Procedure Resources

Cook, Joseph A., Dunnum, Johnathan L., Bogan, Michael, Gannon, William L., Ramotnik, Cindy A., and Terry L. Yates. 2017. Division of Mammals Collection Management Procedures Manual. Museum of Southwestern Biology, University of New Mexico.

Hall, Raymond E. 1962. Collecting and Preparing Study Specimens of Vertebrates. Lawrence, University of Kansas.

References

1. Webster, M.S (ed.). 2017. The Extended Specimen: Emerging Frontiers in Collections-Based Ornithological Research. CRC Press, Boca Raton. ↩︎
2. Hangay, G. and M. Dingley. 1985. Biological museum methods: Vertebrates. Academic Press. ↩︎
3. Simmons, John E. 2014. Fluid Preservation: A Comprehensive Reference. Lanham, MD: Rowman & Littlefield, 347 pp. ↩︎