The evolution of the black wildebeest, Connochaetes gnou, and modern largemammal faunas in central Southern Africa
Date
2005-12
Authors
Brink, James Simpson
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
This study investigates the evolution of modern mammalian faunas in the central interior of
southern Africa by testing the hypothesis that the evolution of the black wildebeest, Connochaetes
gnou, was directly associated with the emergence of Highveld-type open grasslands in the central
interior.
Southern Africa can be distinguished from other arid and semi-arid parts of the continent by the
presence of an alliance of endemic grazing ungulates. The black wildebeest is characteristic of this
alliance. Open habitats are essential for the reproductive behaviour of the black wildebeest, because
territorial males require an unobstructed view of their territories in order to breed. The specialised
territorial breeding behaviour of the black wildebeest is the reason why the black wildebeest is
historically confined to the Highveld and Karoo areas and why it is reproductively isolated from
sympatric blue wildebeest, Connochaetes taurinus. The finds from a number of fossil-rich
localities, dating from the recent past to approximately a million years ago, have been identified.
The remains referred to ancestral C. gnou have been subjected to detailed qualitative and
quantitative osteological comparisons with cranial and post-cranial elements of modern and fossil
reference specimens. This material includes extant southern African alcelaphines and fossil
materials of C. gnou, the extinct giant wildebeest, Megalotragus priscus, and North African fossil
alcelaphines. The results show that cranial changes in fossil C. gnou, particularly the more forward
positioning of the horns, basal inflation of the horns and the resultant re-organisation of the
posterior part of the skull, preceded other skeletal modifications. These cranial changes indicate a
shift towards more specialised territorial breeding behaviour in the earliest ancestral black
wildebeest, evident in the specimens of the c. million year old Free State site of Cornelia-Uitzoek.
Since the territorial breeding behaviour of the black wildebeest can only function in open habitat
and since cranial characters associated with its territorial breeding behaviour preceded other
morphological changes, it is deduced that there was a close association between the speciation of C.
gnou from a C. taurinus-like ancestor and the appearance of permanently open Highveld-type
grasslands in the central interior of southern Africa. This deduction is supported by the lack of
trophic distinction between the modern black and blue wildebeest, suggesting that the evolution of
the black wildebeest was not accompanied by an ecological shift. It is concluded that the evolution
of a distinct southern endemic wildebeest in the Pleistocene was associated with, and possibly
driven by, a shift towards a more specialised kind of territorial breeding behaviour, which can only
funtion in open habitat.
There are significant post-speciation changes in body size and limb proportions of fossil C. gnou
through time. The tempo of change has not been constant and populations in the central interior
underwent marked reduction in body size in the last 5000 years. Vicariance in fossil C. gnou is
evident in different rates of change that are recorded in the populations of generally smaller body
size that became isolated in the Cape Ecozone. These daughter populations, the result of dispersals
from the central interior, became extinct at the end of the Pleistocene.
Description
Thesis (PhD (Archaeology))--University of Stellenbosch, 2005.
Keywords
Gnus -- Evolution -- Africa, Southern, White-tailed gnu -- Evolution -- Africa, Southern, White-tailed gnu -- Africa, Southern -- Phylogeny, Mammals -- Evolution -- Africa, Southern, Animal remains (Archaeology) -- Africa, Southern, Dissertations -- Archaeology, Theses -- Archaeology