UWM Undergraduate Research - Spring 2023
Burn, Chop, Drown: Taphonomy in Action
This semester, Dr. Jean Hudson and I have been working with four undergraduate students awarded research funds through the UWM SURF program to study different aspects of taphonomy in forensic and archaeological contexts.
Taphonomy, or the laws of burial, is the scientific study of the processes that affect an organism after its death until it's discovered. It examines how bones, teeth, and other hard tissues are modified by various physical, chemical, and biological factors over time. Taphonomy involves a wide range of disciplines including archaeology and forensics. By studying taphonomy, scientists can reconstruct the circumstances surrounding an organisms death and work to distinguish postmortem environmental effects from perimortem trauma or other human activity, helping forensic scientists in their goal to establish cause and manner of death and helping archaeologists reconstruct past lifeways.
I attempted to create a comparative collection showing the taphonomic effects of burning. I used fifteen deer ribs in three trials of five bones each. The goal was to have a display from yellow to yellow/brown to brown/black to grey/blue. These colors are supposed to correlate with specific temperature ranges. The comparative collection is to be used by UW Milwaukee’s anthropology department as teaching aids. This experiment proved difficult for two main reasons. First, my grill couldn’t get hot enough to make bone grey and blue. Secondly, the ribs started to break and crack into pieces when charred. Smaller bones and less dense bones are hard to control during a burn.
Burn Barrel Trial 1:
I used 5 partially fleshed deer metapodials, originally intended for the propane grill, atop a grate over the burn barrel. I again attempted to create a comparative collection. This proved even harder because the elements were even further away from the flame and the hooves melted to the bone that created big chunks of brittle soft tissue that just wasn’t burning away. In a way, the hooves protected the bone. In this trial I was only able to get yellow, brown, and black.
Burn Barrel Trial 2:
I used two hind limbs and two forelimbs from a single Elk to simulate human bone and placed them directly on top of the fuel source. I placed them on top and uncovered to simulate a hasty burn. These burned quickly down to gray and white but refused to become unrecognizable ash. Many elements remained after 4 hours of burning. For example, the astragalus, femoral head, proximal and distal tibia all remained. They were in fragments but clear enough to be identified. It became clear that in a forensic context, a criminal trying to dispose of a body this way would still leave lot of evidence.
Burn Barrel Trial 3:
Through 5 trials of experiments, I have created a comparative collection of sharp force trauma with varying tools on varying types of bone. This collection will be used by future students to aid in learning and recognizing the key taphonomic differences sharp tools produce on to different compositions of bone. For this experiment we used fleshed deer metapodials, un-fleshed deer metapodials, and deer ribs in 5 rounds of experiments. The 5 different tools used were a saw, hunting knife, axe, hammer, and a hatchet. For each trial, there were an average of 3 blows to each bone. For the ribs, I tried to create the markings on along the sternal head, mid-shaft, and then the rib head. For the fleshed metapodial limbs, I tried to contain the blows to the main portion of the long bone. However, with the blunt force trauma tools and my lack of experience, it was more difficult for me to contain the blows.
Trial one, I used a saw to a deer rib, un-fleshed metapodial, and fleshed metapodial. The saw left varying amounts of striated marks along all the incisions of all 3 bones. For the deer rib, I noticed the kerfs towards the sternal end were much more defined than the rib head. I could also tell that when I was using the saw that the sternal end was slightly easier to cut through. The kerfs of the un-fleshed metapodial did not go as deep as the deer rib, however, are still visible. You are also able to visualize some splitting of bone at one of the incisions. For the fleshed metapodial, the incision near the distal portion of the bone is much more defined than the one towards the proximal end.
For trial three I used an axe to the three types of bones. The axe produced far different taphonomic markings compared to the first two trials. This was expected, as an axe is a blunt-force trauma tool while a knife and saw are considered to be sharp-force trauma. I was expecting far more breakage and fragmentation since an axe requires velocity in a swing to produce stress on bone. The rib bone broke into three main pieces and multiple small fragments after the three blows to the bone. The three main breaks of the bone created wedge-like fractures. The un-fleshed metapodial managed to stay in one piece after three blows to the axe, but I do have to acknowledge that my form was inadequate which may have impacted the results. I missed the bone a few swings, so I am unsure how many hits fully hit the bone itself. The taphonomy left on the metapodial consisted primarily of chipping of bone from the mid-shaft area. For the fleshed metapodial, my axe form must have improved some. I was able to break the bone into three parts and see similar wedge-shaped breaks, similar to the rib breakage.
For trial four, I used a hatchet to the three bones. This taphonomy was more similar to trials one and two. For the rib, the kerf on the sternal end showed splitting of the bone. I believe this is due to the drawback of the hatchet after it was inserted to the bone, since I swung down on the bone with the tool instead of cutting in a back in forth motion. The mid-shaft kerf on the rib showed a wedge-shaped depression which would be consistent with a blunt-force object. For the un-fleshed metapodial, the bone was already missing a small piece of the distal end. So by the second blow to the bone, the rest of the distal end flew off, even though the. blow was towards the opposite end. The markings on the un-fleshed metapodial were similar in shape to the rib. The most proximal kerf created a large spur bone that I believe was due to the force of the hatchet being withdrawn from bone, similar to what happened with the rib. The hatchet did not leave as defined markings on the fleshed metapodial compared to the other two.
Trial five I used a hammer to the bones. This produced multiple breaks to the rib bone, but not as much fragmentation/shards as the axe did. The breaks on this rib were cleaner but did have a wedge shape. The un-fleshed metapodial remained mostly in one piece after three blows of the hammer, with some minor sheet-like fragment in the mid-shaft. There were minor taphonomic observations made on the fleshed metapodial which I believe to be caused from multiple issues. I do not think I hit this bone as hard as the others, as well as the flesh on it had to provide some sort of protection. You are able to see some markings that have be to believe I hit the bone on an angle rather than directly with the head of the hammer.
Throughout the four week period I monitored the water temperatures in each specimen container. The fresh water specimens stayed at an average temperature of 5.92 degrees Celsius and the salt water specimens stayed at an average temperature of 21.07 degrees Celsius. By the fourth week of the experiment the first freshwater specimen (18-8-2-6) presented skin slippage, Initial adipocere formation, and abdominal bloating subsided. The second freshwater specimen (18-8-2-8) presented the same results. The first salt water specimen (18-8-2-1) presented adipocere formation, wearing away of soft tissue, small areas of bone exposed on arms and legs, black discoloration, and abdominal bloating subsided. The second salt water specimen (18-8-2-2) presented unique results. All of the water In this container evaporated causing dry/leathery skin, mold present on ribs, collapsed abdomen, and small area of bone exposed on arms and legs. Given the visual examination, we can conclude that salt water Increases decomposition compared to freshwater. Since this four week period was only to observe the Initial decomposition stages, over the next three weeks I will continue to observe the specimens for further decomposition.
In my experience, it can be difficult to identify animal bones in an archaeological context. While many bones are distinctive between classes and can be distinguished by someone with a trained eye, it is much more difficult to class the smaller bones, such as pedal phalanges; or broken fragments of long bones without diagnostic features present. I chose to compare some of these more difficult to identify bones of two animals of similar size from different classes: eastern cottontail rabbit (Sylvilagus floridanus) and mallard duck (Anas platyrhynchos). I took photos and data from two specimens of each species, all of a fully developed adult skeletal age. I compared the pedal phalanges of each species to determine if there were any diagnostic features that allowed me to differentiate the two species. I also measured the cortical thickness of several different broken long bones of each species in order to see if there was a difference in cortical thickness between the species that could be used to identify the bone to class level when only a shaft fragment is present.
I found that, though the pedal phalanges of each species are similar, there are some differences that would allow an archaeologist to determine which class it came from. To start, the build of the foot is significantly different between rabbits and ducks, with rabbits having a metapodial and three phalanges per digit, while ducks have fused metapodials and a differing number of phalanges per digit. The difference in metapodials between the two species makes the proximal end of the proximal phalanx of each digit look quite specific to the species. There is a much more distinct notch on the proximal end of the proximal phalanx of the rabbit to fit into the distal end of the metapodial. Conversely, the proximal duck phalanx has a much more flat, planar surface. The distal-most phalanx of each animal, or the claw, is also different between the two species. The duck’s distal phalanx comes to a more blunt point than the rabbit’s, which is sharper and more pointed. The duck distal phalanx is a bit flatter on the plantar side, as well as having a smaller and more square articular end than that of the rabbit. As a whole, rabbits have a flatter plantar surface than the duck phalanges, as well as a more slanted articular facet, while the duck articular facet is more directly vertical. The duck phalanges also have a more distinct bilobed head on each phalanx. Finally, the proximal articular surface of duck phalanges is a more triangular shape, while the rabbit proximal articular surface is more square.
I also compared the cortical thickness of various long bones of both rabbits and ducks. Colloquially, bird bones are thought to be lighter and less dense than mammal bones, so I wanted to see if that assumption carried over to cortical thickness. I used a sliding digital caliper to measure the cortical thickness of several different broken long bones from each species to take several measurements of each location on the bone I measured, then added the measurements together and divided by the number of measurements to find an average cortical thickness of each part of each bone. I then graphed the average thickness by specimen in order to provide a more visual comparison between the species. I found that, with the specimens I measured, there was a distinct difference in cortical thickness between rabbits and ducks, with no overlap between measurements of my specimens. This is a very promising finding, and indicates that it may be possible to identify archaeological specimens to the class level solely by measurement of cortical thickness.
These studies successfully answered the questions I set out to ask, and provide a basis for future experiments as well. The species I studied are also very relevant to Wisconsin archaeology, since both ducks and rabbits are found quite frequently in the area. There is promise in further experiments in this portion of the field as well, with the potential for future studies of a larger variety of species, as well as a larger range of specimen ages. I believe my research provides a solid reason for continuing to study cortical thickness differences between animal classes, since there was distinct and obvious contrast between the measurements of each class in the specimens I used in my experiments.