Number of Fragments
Most zooarchaeologists count and record the total number of fragments for each taxon for a unit of analysis and type of recovery. The unit of analysis is often the whole deposit attributed to single camp or time period. The tallies are often reported separately for each type of recovery, such as for ¼” mesh and 1/16” mesh, because the volume of sediment for each type of recovery may greatly vary. Because of the differences in sediment volume, for our grant project, we primarily counted, presented, and compared bones collected through different mesh sizes separately.
The counts are made for each taxon including everything from the indeterminate animals to those identified to species-level. Sometimes these tallies are referred to as the Number of Fragments or the Number of Identified Specimens (NISP). Sometimes NISP is restricted to species identified to at least a certain level such as family or more precisely, and all of the indeterminate specimens are not include in the NISP count. For the Koster site and Modoc Rock Shelter, all of the bones and shells are counted and referred to as the number of fragments for Koster and NISP for Modoc. For some sites in our study, only bones identifiable to family and/or element were counted for flotation samples. Some specialists only tabulate shells from freshwater mussels and gastropods (snails) if they were identifiable to at least the family or genus. It is important to record and consider how bones were counted when comparing sites. If you only tabulated the identifiable mussel shells, then the percentage of mussels considered as identifiable will likely appear to be artificially high.
Minimum Numbers of Individuals
To determine the Minimum Number of Individuals (MNI) represented in the faunal remains, one has to first pick a unit of analysis. We often consider the whole deposit attributed to a single occupation as the unit of analysis. We report our MNI tallies separately for each type of recovery because different volumes of sediment are represented. We determine the MNI by counting the most abundant singly occurring element for each identified taxon. In this case, the bones from indeterminate categories of animals are not included. An example will help you understand this calculation.
For example, an individual deer has one right humerus and one left humerus. So if there are seven whole left humeri and six whole right humeri from a deposit at a site, then at least seven individual deer are represented.
Calculations of MNI generally consider element, portion, side, completeness, and body size and age if available for each identified taxon. We calculate the MNI for species and then for higher levels such as a genus or family only if it adds to the number calculated for species.
Look at the left humerus (left side of image) and the right humerus (right side of image) and the portions for these white-tailed bones from the comparative collection to help you determine the minimum number of individuals of deer in the sample of bones listed to the right. Image taken by Bonnie Styles.
The image of white-tailed deer humeri from the comparative collection shows a right and left humerus and the labels indicate the portions. Please note that the epiphyses are fused to the shafts in the comparative specimens.
See if you can determine how many individual white-tailed deer are represented in the list below from a sample of bones:
One right unfused proximal epiphysis fragment from a humerus, greater than ½ complete
Three left unfused proximal epiphysis fragments from humeri, greater than 3/4 complete
One right humerus shaft fragment with no epiphyses, less than ¼ complete
One left humerus shaft fragment with no epiphyses, less than ¼ complete
If you counted a minimum of three individuals, then you are correct. An individual deer has a right and left humerus. A humerus has a shaft and a proximal and distal epiphysis. There are three left unfused proximal humeri epiphysis fragments that are greater than 3/4 complete so there have to be at least three deer represented in the sample. The shaft fragments and the right proximal epiphysis fragment could be from these same individuals.
Look at this image of left and right dentaries (top of image) and left and right opercles (bottom of image) from channel catfish in the comparative collection to help you estimate the Minimum Number of Individuals (MNI) for the sample listed to the right. The comparative specimens are from a fish with a standard length of 46 cm. Body size matters when calculating the MNI. Image taken by Doug Carr.
Now let’s try an example with fish. See if you can determine the MNI for this list of skull bones of channel catfish (Ictalurus punctatus) from a sample:
1 right dentary (lower jaw bone) fragment, greater than half complete, standard length 40-48
3 left dentary fragments, less than ¼ complete, standard length 8-16 cm
1 right opercle fragment (plate that covers the gill), less than ¼ complete, standard length 16-24 cm
If you counted a minimum of three individuals, then you are correct. As shown in the image, a channel catfish has a right and left dentary. It also has a right and left opercle. Because three different lengths of channel catfish are present in the sample, there had to be at least three fish. There is only one fish for each length. Because the three left dentary fragments are all less than ¼ complete and you can't see the portions, you don’t know if they could all be from the same bone or from three different bones.
Calculating the minimum number of individuals for large samples of fauna is very time consuming and somewhat subjective. Some animals have numerous identifiable bones and others have few. This difference could result in higher numbers of identifiable fragments for some species. The MNI resolves that bias. MNI can also be used to calculate meat weights based on known weights for kinds of animals. Many researchers prefer to use the Number of Identified Specimens rather than the MNI because it is easier and more objective to calculate. Many studies have shown that interpretations based on NISP and MNI are often similar for sites will good preservation and large samples.
Weights of Bones and Meat
Some zooarchaeologists weigh each bone or all of the bones identifiable for a taxon for a unit of analysis. This process allows them to try to calculate meat weights based on mathematical relationships between bone weight and animal weight.
Many zooarchaeologists calculate the amount of meat provided by a species my multiplying the Minimum Number of Individuals times the average weight for an individual animal. These estimates may consider age and sex if data are available for living animals and the archaeological specimens. Some zooarchaeologists analyze the nutritional value of the meat, and some attempt to estimate the calories provided.
Weights of bones were not analyzed for Modoc or Koster.