Following the suggestion of one of my readers (who has her own great blog at http://bonesandskulls.co.uk/), today’s post is going to be about processing comparative skeletal specimens. I won’t go into the different ways one can obtain dead animals, or any of the state, federal, or international laws governing the acquisition of certain species (but please do look into those before collecting anything!). Today it’s all about decomposition. There are numerous methods one can use to clean a skeleton (and by “clean” I mean get rid of all the smelly, nasty, soft stuff). Which one you use will depend on a number of things including local climate, available space, and time constraints.
The first thing you have to do, regardless of what method you use, is eviscerate, skin, and deflesh the specimen to the best of your ability. Believe me, you want to get as much meat off of the bones as possible! This will cut down on the total processing time and nasty smells. Scalpels work wonderfully for this, but I’ve also used kitchen knives, multitools, and scissors (and pliers for porcupine quills). You can be done some place fancy like a large processing sink in a science lab, or on top of a garbage bag taped to a table or laid out on the ground. I personally use the garbage bag more often than the lab sink. Once you’ve defleshed the specimen as much as possible, you now have a choice:
Cold Water Maceration
Cold water maceration is simple – you place the specimen in a tub of cold or room-temperature water, put a lid or screen over it, and walk away. You can do things like wrap pantyhose around the extremities to keep podials, metapodials and phalanges together (which makes it easy to determine whether they came from the left or right side once you’re all done). You can also add a little borax-based detergent booster (I prefer Biz), which will help speed things along. Overall, though, you’re looking at a few months to a year (depending on species) of processing time. Usually people change out the water every week or so, and at the end you obviously want to rinse the (now disarticulated) elements off very well. This method works wonderfully for things with really delicate bones (e.g., birds, fish, skulls), and you’ll avoid any potential shrinking or warping. But beware the fish – the only time I’ve come close to vomiting during processing was after the cold maceration of a burbot.
Hot Water Maceration (“Boiling”)
This is probably one of the most common processing methods. You place the specimen in a large pot or glass beaker full of water, and heat it until it is almost boiling (do NOT bring it to a full boil!). You maintain the simmer for as many hours as possible at a time, until the specimen is disarticulated and clean. At home I use a big pot (originally intended for crab) and my kitchen stove. At school, I use large beakers on hot plates under a fume hood. Again, depending on species, this can take a long time (for some reason, birds seem to take the longest time for me), but this is by far one of the fastest methods. Adding a small amount of detergent such as Biz, and a smidge of bleach, will help. Be aware, though, that the heat may slightly warp or shrink the bones. And if you accidentally let it come to a full boil (as I have), it will cause the cortex to flake and peel once it’s dry. I have a flaky black bear in my collection, and handling it always creates a horrible mess.
The use of “bug boxes” filled with flesh-eating beetles (Dermestes sp.) seems to be most common in museums. Although the beetles only eat dead flesh (so you don’ t have to worry about being attacked a la The Mummy), I personally hate them. Not only do the beetles themselves smell disgusting and produce a ridiculous amount of waste and dandruff (including larval hairs) that some people develop allergies to, they don’t completely clean the bone. The beetles like to eat flesh, not tendons, which means that there are often little nubbins of tendon left at the insertion points around the joints. (This explains why the Zoology Department interns at The Field Museum are called “Pickers”… when I was there they spent a large portion of their time picking whatever the dermestids didn’t eat off of the bones). Now, for biologists this might not be such a bad thing, but for zooarchaeologists one of the major things we look at on a skeletal element are the articular facets! I’ve looked at many osteological specimens at many museums, and found that most of them were worthless to me. Very irritating. Also, you have to buy these suckers from specialized dealers – anywhere from 300 to 1,000 adult beetles at a time. And remember, in order to maintain a colony you have to keep feeding them carcasses, otherwise they’ll starve to death. Depending on the size of your operation, this can be problematic.
Manure (herbivore only!!!) is a wonderful way to process animal specimens. It is the preferred method of the Alaska Consortium of Zooarchaeologists (headquartered in Anchorage, Alaska). We usually get horse manure from one of the local barns, but we’ve also picked up camel manure from the zoo. Any herbivore should work well, and people are usually very willing (if surprised) to give away poo. It works similarly to cold water maceration in that you dump the carcass in a tub of some kind (preferably wrapped in window screen to make it easier to find all of the elements once the specimen is done processing), cover it with manure, throw a lid on it, and walk away. Unlike maceration you don’t have to change out the water or tend to it, but you do have to do more work once the manure has worked its magic. Cleaning poo off of the bones takes time, and no one likes working with feces (even though at this point, if everything has gone well, it just smells like dirt). It usually takes a few months for the little microbes and things in the poo to get the specimen clean (again, depending on size and species… It took my porcupine 6 months). Another thing to keep in mind is climate – manure works well in cooler temperatures (I’m assuming you’ll be keeping the tub outside somewhere). It’s okay to overwinter it outside, although you’ll probably need to add some fresh manure come spring. In California, it seems like manure doesn’t work as well – It gets too hot, and the tiny critters we want end up dead while the flies breed like mad.
This is a new technique for me – I first heard about it from Michael Etnier (http://www.appliedosteology.com/). After the manure method wasn’t working out so well for our Anthropology Department here in California, a bunch of us got together (funded by the UCD Zooarchaeology Lab) and built a large, above-ground sandbox in my back yard. Following the same principle as before (wrap it in window screen, cover it, walk away), we finished processing two sea lions and a goat that had been languishing in hot, fly-infested manure, and are just about ready to pull out a harbor seal and a cow head. The sterile sand facilitates autolysis, which basically means that the enzymes in the carcass devour the tissue. It’s been working very well so far, although my poor husband did have to water the sandbox for me over the field season, as the specimens were beginning to bake instead of melt. Apparently you don’t have to do that in the Pacific Northwest. If you go for the sandbox method, just keep your local weather conditions in mind.
A fantastic resource for specimen processing is Lee Post’s Bone Builder’s Notebook (http://theboneman.com/). Based out of Homer, Alaska, Lee is a self-described “bone builder”, well-known for his incredibly useful hand-drawn osteology books and innumerable projects articulating skeletal specimens for schools and museums. He just revised the book this year, so it’s as up to date as you could hope for. Another good resource is the blog of Jana Miller (http://bone-lust.blogspot.com/), who writes about skeletal processing from a naturalist and artist’s perspective.