THE EVOLUTION OF THE BLACK WILDEBEEST, CONNOCHAETES GNOU, AND MODERN LARGE MAMMAL FAUNAS IN CENTRAL SOUTHERN AFRICA by James Simpson Brink *** Dissertation presented for the Degree of Doctor of Philosophy at the University of Stellenbosch. Promoter: Prof. H.J. Deacon. December 2005 ii DECLARATION I, the undersigned, hereby declare that the work contained in this dissertation is my own original work and that I have not previously in its entirety or in part submitted it at any university for a degree. Signature: ……............................... Date: 22 March 2005 iii 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. iv OPSOMMING Hierdie studie ondersoek die ontstaan van moderne soogdier-faunas in die sentrale binneland van suider-Afrika deur die hipotese te toets dat die evolusie van die swart-wildebees, Connochaetes gnou, ge-assosieer en moontlik die gevolg was van die verskyning van Hoëveld-tipe oop grasveld in die sentrale binneland. Suider-Afrika word onderskei van ander droë en half-droë streke van die kontinent deur ‘n alliansie van endemiese grasvretende hoefdiere. Die swart-wildebees is kenmerkend van hierdie alliansie. Oop habitat is noodsaaklik vir die paringsgedrag van die swart-wildebees, aangesien territoriale bulle ononderbroke sig van hul territoria benodig om te kan voortplant. Die gespesialiseerde territoriale paringsgedrag van die swart-wildebees verklaar waarom sy historiese verspreiding tot die Karoo and Hoëveld beperk was en ook sy reproduktiewe isolasie van simpatriese blou- wildebeeste, Connochaetes taurinus. Die fossiel-oorblyfsels van ‘n reeks lokaliteite, wat in ouderdom strek vanaf die onlangse verlede tot ongeveer een miljoen jaar, is uitgeken. Kraniale sowel as postkraniale elemente van voorouer-C. gnou is met elemente van moderne en fossiel eksemplare vergelyk. Hierdie eksemplare sluit materiaal in van moderne suider-Afrikaanse Alcelaphini, fossiel-materiaal van C. gnou, die uitgestorwe reuse-wildebees, Megalotragus priscus, en Noord-Afrikaanse fossiel-Alcelaphini. Die resultate wys dat sekere anatomiese aspekte van die skedel, soos die vooroor-gebuigde horingvorm, die vergrote horingbasisse en die gepaardgaande herorganisering van die skedelbasis, ander skelet-veranderinge voorafgegaan het in die materiaal van Cornelia-Uitzoek, ‘n Vrystaatse lokaliteit van ongeveer ‘n miljoen jaar oud. Hierdie kraniale veranderinge wys dat daar ‘n gedragsverkuiwing na ‘n meer gespesialiseerde vorm van territoriale gedrag by die eerste voorouer-swart-wildebeeste was. Aangesien die territoriale gedrag van swart- wildebeeste slegs kan funksioneer in oop habitat en aangesien kraniale aanpassings, wat met territoriale gedrag ge-assosieer word, veranderinge aan ander skelet-dele voorafgegaan het, word dit afgelei dat daar ‘n nou verband was tussen die ontstaan van C. gnou uit ‘n C. taurinus-agtige voorouer en die verskyning van Hoëveld-tipe oop grasvelde. Hierdie afleiding word gesteun deur die feit dat moderne swart- en blou-wildebeeste nie trofies onderskeibaar is nie, wat ook impliseer dat die evolusie van die swart-wildebees nie met ‘n ekologiese aanpassing gepaardgegaan het nie. Die slotsom is dat die evolusie van ‘n suidelike endemiese wildebees-spesie gedurende die Pleistoseen onderhewig was aan die verskyning van ‘n gespesialiseerde vorm van territoriale voortplantingsgedrag, wat slegs in oop habitat kan funksioneer. Daar is ook beduidende post-spesiasie veranderinge in liggaamsgrootte en liggaamsproporsies in fossiel-vorme van C. gnou. Die tempo van die veranderinge was nie konstant nie en populasies in die sentrale binneland het merkbaar verklein in die laaste 5000 jaar. Geografiese veranderinge is gedemonstreer in ge-isoleerde populasies met verkleinde liggaamsgrootte in die Kaapse Ekosone. Hierdie dogter-populasies, die produk van vroeëre biogeografiese verspreiding vanuit die sentrale binneland, het uitgesterf teen die einde van die Pleistoseen. v CONTENTS DECLARATION.............................................................................................................................. ii ABSTRACT..................................................................................................................................... xi OPSOMMING................................................................................................................................. iv CONTENTS...................................................................................................................................... v ACKNOWLEDGEMENTS........................................................................................................... xii LIST OF FIGURES ...................................................................................................................... xiv LIST OF TABLES ..................................................................................................................... xxvii CONVENTIONS......................................................................................................................... xxix CHAPTER 1: INTRODUCTION................................................................................................... 1 THE ARID CENTRES OF AFRICA............................................................................................................1 AIM OF THE STUDY....................................................................................................................................1 DISCOVERY OF A PLEISTOCENE CAPRINE IN SOUTHERN AFRICA ..........................................4 CHAPTER 2: HISTORICAL PERSPECTIVE ............................................................................ 5 INTRODUCTION ..........................................................................................................................................5 THE CENTRAL INTERIOR ........................................................................................................................5 AREAS NORTH AND WEST OF THE VAAL RIVER.............................................................................8 THE VAAL RIVER GRAVELS .................................................................................................................10