The current study uses the head and neck of giraffe (Giraffa camelopardalis)
as a model for tracking the course of evolutionary change. Gould (2002) has argued
that there are three main avenues of evolutionary change that result in the genesis of
new morphologies. These are phylogenetic constraints, structural or allometric
scaling laws of form, and specific unique adaptations. It is well known that the
unique characteristic of the giraffe is its extremely long neck and yet, it only has
seven cervical vertebrae. To study the neck the vertebral body lengths of different
aged giraffes were measured to determine the contribution of the cervical vertebrae to
the total vertebral column. The vertebrae of several extant ungulates as well as those
of fossil giraffids were used as a comparison with the giraffe. CT scans were used on
several giraffe skulls to study the extent of the frontal sinus in the giraffe in an attempt
to explain why the giraffe evolved such a large frontal sinus. The vertebral columns
and skulls of several ungulates, including the okapi (Okapia johnstoni) were also used
to compare with the results obtained from the giraffe. Immunohistochemistry was
used to study the medulla and spinal cord sections of the giraffe to determine if the
location and size of the nuclei remained unchanged to the basic ungulate or
mammalian plan in spite of the unusually long neck, or if this long neck led to
changes in the nuclei found in those regions. The results of these stains were all
compared to the published literature available. Although more studies need to be
conducted on other ungulates to conclusively determine why giraffe have evolved a
long neck, overall the results showed that the anatomy giraffe head and neck remained
true to the basic mammalian plan, with very little changing in terms of it morphology.
The giraffe brain and spinal cord also resembled that of a typical ungulate. This
leads to the conclusion that constraints and allometric scaling laws of form play a
greater role than previously thought in the evolution of extreme morphologies.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/5853 |
| Date | 01 December 2008 |
| Creators | Badlangana, Ludo Nlambiwa |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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