This study successfully utilised the non-invasive neuroimaging techniques of
Computerised Tomography (CT) and Magnetic Resonance Imaging (MRI) to
establish that dolphins have high relative brain size values, transcending the
primate range for neocortex volume and neocortex ratio. Bottlenose dolphins
superseded human values of the neocortex ratio and common dolphins
marked the upper limit of the range for the dolphin species under
investigation. In addition this study was the first to find a correlation between
sociality and neocortex ratio in dolphins (R.I.M. Dunbar, pers.comm), which
supports the hypothesis of neocortical development in relation to
sociality/group size (Sawaguchi & Kudo 1990; Dunbar 1992) and
social/Machiavellian intelligence (Byrne & Whiten 1988; Byrne 1995). The
study devised new measures of relative brain size, including the grey-white
matter and higher cortical ratios and these require further research before
verification of their efficacy. Equations were calculated to allow estimation of:
(1) MRI values of total brain volumes from CT values, (2) total brain volume
from cranial volume using CT, (3) cerebral cortex volume from cranial or total
brain volume (CT) and (4) cerebral cortex and cerebellar cortex volume from
total brain volume (MRI). The effects of freezing and defrosting on volume
and density of CT and MRI values were investigated. Additionally, the
relationship between relative brain size (EQ) and sociality was investigated
for other dolphin research, using previously published figures, but no
significant correlations were found. Finally, dolphin values were compared to
primate values for neocortex volume and neocortex ratio with the finding that
the only primate within the dolphin range of neocortex was the human,
positioned higher than the solitary humpback dolphin, but below all of the
other, more socially complex, dolphin species. / Thesis (M.A.)-University of Natal, Durban, 1996.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/7460 |
| Date | January 1996 |
| Creators | Tschudin, Alain Jean-Paul Charles. |
| Contributors | Peddemors, Victor M., Henzi, S. Peter., Royston, D. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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