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Project Implementation and Data

Data Collected and Project Implementation

The following data was obtained from a collection of Standlooper skulls held at the Slave Lodge of the Iziko Museums in Cape Town, South Africa.

 

Strandlooper Skull Measurements

Specimen

Name

CC (mL) Orbital Breadth (mm) Orbital Height

(mm)

Foramen Magnum Length

(mm)

Foramen Magnum Breadth

(mm)

SAM-AP 5055 1350 37.93 31.79 36.02 33.95
SAM-AP 5051 1350 38.61 28.58 36.91 27.25
SAM-AP 50521 N/A 38.52 32.11 35.52 28.05
SAM-AP 50532 1310 41.16 33.79 37.82 31.32* MAX.
SAM-AP 11293 1320* 40.25 N/A N/A N/A
SAM-AP 46614 N/A 38.6 N/A N/A N/A
SAM-AP 46325 N/A 35.86 30.53 N/A N/A

Notes: 1SAM-AP 5052 was found in two pieces and we determined that its cranial capacity could not be determined to a helpful accuracy. 2SAM-AP 5053 damage to the foramen magnum points of measurements left us with a maximum value for the possible foramen magnum breadth. 3SAM-AP 1129 suffered damage to the anterolateral part of the basicranium and the cranial capacity is likely an overestimate. 4SAM-AP 4661 was missing the entirety of its basicranium. No accurate cranial capacity could be calculated. 5SAM-AP 4632 had missing parts of the right temporal and parietal regions as well as the occipital and thus its cranial measurements could not be estimated. *indicate estimated measurements.

I attempted to collect data from 7 Strandlooper skulls with the help of Jessica Kittelberger. Although we initially intended to use millet seed to measure cranial capacity, we were unable to obtain seed on such short notice and opted to use white rice as a substitute due to their similar densities.

At the museum I quickly discovered that the cranial capacity of four skulls (SAM-AP 5052, SAM-AP 1129, SAM-AP 4661, SAM-AP 4632) could not be measured with accuracy due to the absence of significant fragments of the cranium. Additionally, the fragmentary state of SAM-AP 1129 and SAM-AP 4661 made measuring orbital height impossible. For specimen SAM-AP 4632, only orbital measurements could be taken. Thus, my initial sample of seven was reduced to three that were complete enough for both orbital and cranial measurements as reflected in the table above.

Using similar methods and formulas as in Short (2016) and Radinsky (1967) for controlling for body size using foramen magnum measurements, the following charts and graphs were constructed.

 

Specimen

Name

CC (mL) Orbital Size (mm) Foramen

Magnum Area

(mm2)

SAM-AP 5055 1350 34.86 960.45
SAM-AP 5051 1350 33.60 789.95
SAM-AP 5052 - 35.32 782.52
SAM-AP 5053 1310 37.48 930.32
SAM-AP 1129 1320* - -
SAM-AP 4661 - - -
SAM-AP 4632 - 33.20 -

Mean CC = 1332.5

 

Mean Orbital Size = 34.892

 

Mean Foramen Magnum Area = 865.81

 

Standard Deviation = 20.616

 

Standard Deviation = 1.689

 

Standard Deviation = 92.755

 

orbital-and-body-size

 

cc-and-body-size

 

South Africa has its southernmost point at 35°S and northernmost point around 22°S. Given that the skulls originated in the Knysna and Plettenberg Bay areas, they most likely dwelled in the southernmost region of South Africa around 34°S. In according to Short’s data (2016), our average orbital size at this latitude should be around 36 mm. Although I was able to perform a linear regression, it is difficult to extrapolate the data in a way that leads to a sound and accurate conclusion. However, the mean of the five orbital size measurements appears to fall significantly below the predicted values for the given latitude. I do not feel that a conclusion about the cranial capacity in relation to orbit size can be properly made based on my three data points.

During the collection of this data, I also did not take light measurements for various reasons. Because these studies focus on low-light conditions, perhaps it would be best to conduct light measurements at the times where, in theory, eyes had to strain themselves further and the extent of their acuity was truly tested. This perhaps would take place during the winter months and not during the summertime during which we were visiting. Additionally, it was difficult to determine when exactly the time of “peak activity” would take place as our hosts were generally very active in different ways throughout the day.

It is unfortunate that I cannot come to a sound conclusion due to sample size. However, Short’s (2016) publication is a document I had not come across during my preliminary research despite my background readings. Her findings however, did resolve some of my reservations about the correlation between orbit size and cranial capacity. Her data demonstrates that while orbit size and latitude show partial significant correlation, there does not seem to be a pattern between these variables and cranial capacity. With a sample of over 2,000 specimens, extrapolations and conclusions for this study are made more soundly. I am glad I am able to know that orbit size (and presumably visual acuity) does not appear to significantly impact brain size. Growing an increasingly large brain seems overwhelmingly energetically expensive for the kind of work required to acquire food resources at the latitudinal extremes.

Although I am disappointed at the inconclusive nature of my project, through it I was able to experience the processes that academics go through to answer their questions and perhaps even find themselves at the beginning of a new project.