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| Highlights |
Lesley
Gregoricka
Research Training Program, 2003
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CSI Sheep: Skeletal Reconstruction and Demographic Analysis Introduction Last Spring a mysterious box of animal bones was discovered in a dark corner of the attic at the Smithsonian Institution’s Natural Museum of Natural History. The box contained the jumbled skeletal remains of what appeared to be sheep, as well as a variety of other mammals. No identification of any sort was found on or within the box, no explanation as to who collected the material, where it was from, or when it had been acquired. Thus, by investigating the clues provided by the bones and the box itself, the mystery began to unfold.
A variety of substances were used as packing material to protect the bones, shedding light on the origins of the mysterious box and its contents. However, not all clues turn up successful leads. For instance, rock samples from the box included limestone, sandstone, and clay, yet these minerals can be found on every continent on earth. Similarly,
the insect nests and casings found are as universally spread as the
rocks. Other clues proved more useful, such as pieces of cement and
tile, suggesting the bones may have been buried on a farm, where underground
tile is commonly used to irrigate fields. Most helpful of all was an
unusual pod found amidst ordinary straw. The plant comes from the Genus
Moringa, a group found only in tropical climates. This information
narrowed the box’s origins to the continents of Africa and Asia.
Also, a British fruitcake tin unearthed from the bottom of the box dated
the box from 1870-1940, a time range critical in establishing who collected
the creatures. While the mysteries of the box still exist, interpreting
its clues adds to the story the bones tell.
The
reconstruction of the skeletal remains of the sheep was achieved through
the examination of the varying stages of epiphyseal fusion on the proximal
and distal ends of the long bones. In determining what level of fusion
a bone had reached as well as identifying characteristics unique to
specific individuals, the bone could be reunited with its pair. Thus,
all long bones were paired to try and estimate how many individual sheep
the box contained. Using the minimum number of individuals (MNI) formula,
the box was determined to hold a minimum of 73 sheep.
Examining
the demography of the herd was critical in that it could reveal what
had happened to these sheep. In order to do so, the ages of the individuals
needed to be ascertained. The different stages of bone fusion provided
an excellent ageing guide, as a demographic age profile of survivorship
can be derived from the formula: (F
+ (J x 0.5)) / MNI Also,
tooth eruption and wear sequences were applied to mandibles not only
in order to age the individuals but to measure its correlation with
the ages provided by measuring the epiphyseal bone fusion.
In a normal, managed (domestic) herd providing meat and milk, the proportional representation of the population decreases with age; in other words, more sheep die or are culled as they get older, so a small population of older adults with a large population of newborns is to be expected. However, an unusual number of newborns and older adults dominate the demography of the box, suggesting that a catastrophic, mass die-off occurred, selectively picking off the weakest members of the population. Naturally, the very young and the very old would be much more susceptible to disease or an early winter then the stronger, young population. Also, the sheep appear to have been buried in order to deflesh the bones, suggesting this was no cumulative butchery scheme but a single catastrophic incident. Adding to this argument is the lack of butchery marks on the bones, indicating that the sheep were not killed for food. Consequently, the composition of the boxed individuals suggests the representation of the weaker portion of a population, caused by some sort of natural disaster, and not a complete herd or mass slaughter.
Special thanks to the University of Notre Dame, Mindy Zeder, Bruce Smith, Rob Losey, Dave Rosenthal, Deb Hull-Walski, Jeremy Jacobs, John Ososky, Sorena Sorensen, Risa Arbolino, Eric Hollinger, Abigail Moore, Aaron Goldberg, and Gary Hevel. This
research was supported by the University of Notre Dame NMNH Internship
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