Student Guest Post: Makenna Lenover on Age Determination

During the fall semester (Sept-Dec 2018), students from Bryn Mawr and Haverford helped to clean and catalog the remains at Rutgers-Camden as part of a praxis course led by Professor Maja Šešelj. The following post if from one such student  --- Bryn Mawr student Makenna Lenover.  Makenna has conducted past research on epiphyseal fusion and is interested in developmental processes​.

How to Determine the Age of a Subadult Individual Based on Bones

By Makenna Lenover, Bryn Mawr College

When working with skeletal remains, anthropologists want to understand who are the people represented by those remains. Whether they were young or old at the time of death is one of the first questions we ask. Using developmental stages and/or evidence of wear-and-tear associated with aging, especially old age, is what we call skeletal age estimation. It is one of the core components of producing a biological profile, a reconstruction of the individual as they would have been recognized during life, including age, sex, ancestry, stature, pathology and trauma. By looking at bones and comparing them to established models, biological anthropologists can estimate the age of the individual.

When estimating the age of subadults from bones, we look at the process we call epiphyseal fusion (FIG 1). When humans (and other animals, for that matter) are born, most of their bones consist of many more pieces than in adulthood, and some bones (such as some wrist and ankle bones) are not even present yet. In the arm and leg bones, the main shaft of the bone is separated by a growth plate from what we call an epiphysis, a piece that forms the joint end and joint surface of the bone. In addition to the limb bones, epiphyses are also present in the vertebrae, and the bones of the pelvic and shoulder girdles.  As we age, the epiphyses fuse to the main part of the bone on a fairly regular schedule. Understanding the timing of which epiphyses fuse at what age can provide an estimate of an age range for an individual. For example, the humeral head (the part of the upper arm bone that makes the shoulder joint) fuses to the shaft of the humerus between 16 and 23 years of age (Schaefer et al., 2009). If the epiphysis is not attached at all, the individual is most likely younger than 16, and if the epiphysis is fused and there is no trace of the fusion process anymore, the individual is most likely older than 23. There are also established sequences that describe the order in which an individual is expected to fuse, though one has to keep in mind there is always variability among individuals and populations (Schaefer & Black, 2007; Lenover & Šešelj, 2018). For example, the distal femur (the part of the thigh bone that forms the knee) is most likely to fuse before the femoral head (Lenover & Šešelj, 2019).

These age estimation techniques have been incredibly useful in the Arch Street Project, allowing us to determine the age of buried individuals, and therefore, demographic makeup of the cemetery, as well as determine the number of individuals represented by the commingled, salvaged remains.

Box RU- 19 is a great example showing how this technique was utilized (FIG 2). The box contained an assortment of remains from multiple individuals.

One proximal humerus in the box showed what is categorized as stage 1 fusion (where the epiphysis is fused to the shaft, but the process isn’t complete yet, FIG 3). While there were no remains to identify the sex of this individual, the stage of fusion means the individual was between 17-23 years of age if female, and 16-23 years of age if male (Schaefer et al., 2009).

After identifying this individual as a subadult, it was important to see if the other remains in the box corresponded with what one would expect if they also belonged to that individual. While all the other remains exhibited complete fusion, one distal femur was also in stage 1 and not fully fused (FIG 4). This indicates the individual to whom this femur belonged to was between 15-24 years of age if male and 12-22 years of age if female (Schaefer et al., 2009).

Through this analysis, we can determine that these bones most likely represent one individual aged 17-22 years if female, and aged 16-23 years if male. Although they may have come from two separate individuals, the developmental overlap allows us to assume that they most likely represent the same individual. This is further supported by the other remains in the box, all of which came from an older individual.

Ultimately, through this analysis, the minimum number of individuals in this box is two, an individual aged 16-23 and one older than 23 years. Although not an exact measurement, by examining the fusion of epiphyses to long bones, we can determine demographic information of the remains recovered from the First Baptist Church cemetery, even from remains which are fragmentary or commingled. Furthermore, cross-referencing the demographic information obtained through anthropological analyses with the historical record can help us better understand how the cemetery was organized, and whether the age-at-death of the individuals buried there affected their preservation and recovery.

References

​Lenover, Makenna & Šešelj, Maja. (2019). Analyzing Population Variation in the Fusion Sequence of Primary and Secondary Ossification Centers in the Human Skeleton. American Journal of Physical Anthropology 168 (S68)   

Schaefer, Maureen & Black, Sue. (2007). Epiphyseal Union Sequencing: Aiding in the Recognition and Sorting of Commingled Remains. Journal of Forensic Science 52: 2 277-285.

Schafer, Maureen, Black, Sue, & Scheur, Louise. (2009). Juvenile Osteology: A Laboratory and Field Manual. Elsevier Academic Press: Oxford