South African Journal of Science VoL 93 April 1997 50 YEARS OF'MRS PLES' : RESEARCH BRIËFS 171

Variability in Plio-Pleistocene climates, habitats,and ungulate biomass in southern AfricaJ. Francis Thackeray and S. Reynolds

Vrba,t and de Monecal and Bloemendal2 have emphasised the importance of climaticchange, particularly temperature, in the context of evolution on the African continentwithin the past 5 miLlion years. There is no doubt that long-term changes in climate wouldhave affected African habitats, which in turn would have affected the distribution andabundance of populations of various mammalian taxa, incLuding ungulates and hominids.In this study we explore relationships between oxygen isotope ratios (as determinedfromShackleton's3 analysis offoramin{era from deep-sea cores), and estimates of ungulatebiomass as determined from faunal assemblages from Plio-Pleistocene sites in southernAfrica, using an approach outlined previously.a We go further to assess temporalvariability in ungulate biomass in terms of changes in habitat, gene pools and hominidevolution.

Damuths has previously shown a generalrelationship between mean adult bodyweight and population density of mamma-lian taxa. The relationship has been usedin conjunction with data on modern Afri-can ungulates to obtain ungulate biomassfor areas in sub-Saharan Africa.a Esti-mates of mean adult body mass of anymammalian species is a requirement if thesame relationship is to be applied to faunalassemblages from palaeontological sitesof known age. For purposes of this study,we have obtained the following generalequation for estimating mean adult bodymass (MAB) from first lower molardimensions (Mt), based on collections ofextant mammalian species represented incollections at the Transvaal Museum:

Log MAB = 3.4421og Mr - 2.263 (r = 0.91)

We have used this relationship, in combi-nation with faunal data from Plio-Pleis-tocene sites in the interior of southernAfrica,6 to estimate ungulate biomass forparticular assemblages of ungulate taxafor which age estimates are available.Included in this analysis are assemblagesfrom Sterkfontein (Members 4 and 5),Swartkrans (Members 7,2 and 3), Krom-draai A, Kromdraai B (Member 3), Maka-pansgat, Plovers Lake, Cornelia,Florisbad, Equus Cave and the Cave ofHearths. The estimates of ungulate bio-mass (UB) for inland South Africanassemblages were obtained using theapproach described by Thackeraya formodern fàuna from sub-Saharan environ-ments. The results were then compared topene-contemporaneous oxygen isotoperatios obtained from Plio-Pleistocenedeep-sea cores,3 averaging isotope datawithin intervals of circa 100 000 years.

The following relationship was obtained:UB = 25.8 6 t{O -72.9, (r = 0.75)

where UB refers to ungulate biomass pre-dicted for past environments in the interiorof southern Africa (including the Sterk-fontein valley), in units of kilograms perhectare (kg ha-'). This equation was thenused to assess ungulate biomass variabilityfor southern African palaeoenvironments,based on Shackleton's high resolutionoxygen isotope record from deep-seacores (ODP sites 677 and 846). Results areshown in Fis. 1.

South African inland siûEs

1.0 2.O 3.0

Millions dy€ars before presont

Fig. 1. Estimated ungulate biomass (kg per hectare) for interiorregions of southern Africa including the Sterkfontein valley, SouthAfrica. Relatively low ungulate biomass values can be associated witha relatively high degree of woodland and forest cover, during periodsbetween 3 and 2 million years ago, as opposed to higher ungulate bio-mass values for later intervals, associated with a greater degree ofmixed grassland savanna. Such fluctuations in ungulate biomass atintervals of less than 100 000 years imply episodes of expansion ofwoodland and forest habitats (in warm, moist intervals), followed bycontraction and fragmentation of such habitats during cooler intervals,allowing for gene flow between certain populations (including homin-ids). Episodic gene flow may have contributed to the perpetuation oflineages.

Two observations can be made, usingmodern ungulate biomass estimates andpresent-day Afiican habitats as a frame ofreference,a for assessing relative changesin ungulate biomass in the interior regionsof South Africa:

1) Relatively low ungulate biomassestimates are obtained for the periodbetween 3 and 2 million years ago (Myr),associated with limited temooral variabil-ity in biomass.

2) Higher biomass estimates areobtained within the period between 2 and1 Myr, associated with an increaseddegree of temporal variability in biomass.

3) Yet higher ungulate biomass esti-mates are obtained fbr the period since 1Myr, associated with a still greater degreeof temporal variability.

From the study of ungulate biomass inmodern Afiican habitats,4 it was evidentthat low biomass estimates can be associ-ated with woodland and forest environ-ments; higher ungulate biomass estimatescan be associated with mixed woodlandsavanna habitats. The low ungulate bio-mass estimates for the interior regions ofsouthern Africa between 3 and 2 Myr canbe interpreted in terms of a greater degreeof woodland and forest, as compared tomodern environments in the same area.Higher ungulate biomass estimates forlater periods, associated with a greater

degree of temporalvariability in biomass,can be interpreted interms of a greaterdegree of mixed grass-land savanna and agreater temporal varia-bility in habitats, atintervals of less than100 000 years.

We infer that wood-land habitats can haveexpanded and con-tracted within intervalsof less than 100 000years, in response toglobal changes in cli-mate (primarily tem-perature), associatedwith Milankovitch cy-cles within the last 3million years. Todaywoodland habitats inparts of subequatorialAfrica separate Ser-engeti grasslands inEast Africa from grass-lands on the highveldof South Africa. How-

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172 50 YEARS OF,MRS PLES,: RESEARCH BRIEFS South African Journal oJ Science VoL 93 April 1997

Emphasis on Human Origins, eds E.S. Vrba,G.H. Denton, T.C. Partr idge and L.H. Burckle,pp. 262-288. Yale University Press, NewHaven.

3. Shackleton N.J. (1 995). New data on the evo-lut ion of Pl iocene c l imat ic var iabi l i ty . ln Paleo-climate and Evolution, with Emphasis onHuman Oi lgns, eds E.S. Vrba, G.H. Denton,T.C. Partridge and L.H. Burckle, pp.242-248.Yale Univers i ty Press, New Haven,

4.Thackeray J.F. (1995). Explor ing ungulatedivers i ty , b iomass, and c l imate in modern andpasl environments. ln Paleoclimate and Evo-lution, with Emphasis on Human Origins, edsE.S. Vrba, G.H. Denton, T.C. Partr idge andL.H. Burckle, pp. 479-482. Yale UniversityPress, New Haven.

5. Damuth J. (1981). Populat ion densi ty andbody s ize in mammals. Nature29O,699-700.

6. Smithers R.H.N. (1983). The Mammals of theSouthern Af rican Subreglon. University o{Pretor ia, Pretor ia.

The authors are in the Department of Palaeon-tology and Palaeoenvironmental Studies,Transvaal Museum, P.O. Box 413, Pretoria,000 I South Africa.

ever, episodic cold or cool intervals, occur-ring at intervals of 100 000 years or less,would have led to repeated episodes offragmentation of woodland habitats, allow-ing for episodic gene flow to occurbetween populations of various taxa (e.g.wildebeest) that would otherwise havebeen separated by woodland, as is the casetoday for East African and South Africanpopulations of blue wildebeest, Connocha-etes taurinus, a single species separatedtoday by Miombo woodland. We suggestthat episodic expansion and contraction ofwoodland habitats (occurring at intervalsof less than 100 000 years) were of suchshort duration that speciation

'events'

would not always be expected as a result ofhabitat fragmentation linked to climaticchange over the African continent; instead,high genetic variability may have beenmaintained within lineages, such thatboundaries between species and genera(hominid or ungulate) may be especiallydifficult to recosnise.

We recommend that hominid fossilsfrom sites in East and South Africa bestudied without necessarily attempting to'pigeon-hole' particular fossils into one orother taxon, recognising that boundariesbetween taxa may be blurred on accountof episodic expansion and contraction ofhabitats, associated with repeated episodesof gene flow between populations of taxathat were only temporally isolated by hab-itat changes.

This research has been supported by a grantfrom the Foundation for Research Develop-ment.

1. Vrba E.S. (1995). On the connectionsbetween oaleoclimate and evolution. ln Pale-oclimate and Evolution, with Emphasis onHuman Origins, eds E.S. Vrba, G.H. Denton,T.C. Partr idge and L.H. Burckle, pp. 24-48.Yale University Press, New Haven.

2.De Menocal P.B. and Bloemendal J. (1995).

Pl io-Pleistocene c l imat ic var iabi l ty in sub-tropical Afr ica and the paleoenvironment of

hominid evolut ion: a combined data-modelapproach. ln Paleoclimate and Evolution, with

Evaluating public awareness of 6Mrs Ples' andpalaeontological heritageJ.F. Thackeray and Kathryn Mathers

Museums in South Africa are positionedto play a fundamental and vital role inimproving science and technology educa-tion, and raising awareness of our richpalaeontological heritage. Their objecfcantred educational approach is appropri-ate for people of all ages and educationalachievement. In South Africa, manymuseums are already in line with the newapproach to school education, which ismultidisciplinary and skills-orientated.Museum programmes, however, like mosteducational programmes, are seldom eval-uated. At present we do not have a clearidea of the impact of activities and dis-plays at our museums, in terms of educa-tional value, attitudes of visitors and theirperception of a subject.

Palaeoanthropology in this country is aheld that has not been well covered inschool curricula, and only tentativelyaddressed by many museums. The Trans-vaal Museum is promoting public aware-ness of South Africa's palaeontologicalheritage in 1997, the year in which the50th anniversary of the discovery of 'Mrs

Ples' is celebrated. This offers an opportu-nity to evaluate knowledge before andafter publicity associated with exhibitions,including the display of the original 'Mrs

Ples', during the month of April, at theTransvaal Museum in Pretoria and then at

the Science Festival in Grahamstown.We have launched a long-term project

to evaluate the effect of certain museumexhibitions and their educational, outreachand lecture programmes on the knowledgeand perceptions of the South African pub-lic. The project started at the end of 1996when we established a database on publicknowledge of fossils, focusing on 'Mrs

Ples' in particular.A single-page questionnaire was used to

interview 502 people in the Pretoria areain November and December 1996, and inJanuary 1997. Most of the respondentswere interviewed in shopping centres andat the Pretoria Zoo, while a subsampleincluded people at the Transvaal Museum.Where necessary, interviewers translatedthe questions for respondents.

The majority of respondents (approxi-mately 607o) were African languagespeakers, about 20Vo were Afrikaansspeakers, and another 207o spoke English.Most of the respondents (about 807o) werebetween the ages of 18 and 45 years.Approximately ljVo were younger than 18,and almost 107o were older than 45 years.

Professionals and students account foralmost 507o of the metropolitan sample;the other 507o include individuals in serv-ice, clerical and production industries, aswell as housewives and schoolchildren

(each comprising about 10Vo of the sam-ple, respectively). People in the technicalprofessions (27o) and retired individualsare under-represented. The sample istherefbre not representative of the SouthAfrican population, but is a good crosssection of a metropolitan community.

Results are presented first for the metro-politan sample, excluding individuals vis-iting the Transvaal Museum. Only l3.3%oof this sample said they had heard of 'Mrs

Ples', and a slightly higher proportion(18.0%) had heard of australopithecines.A yet larger proportion of the sample(457o) knew about fossils. Surprisingly,given the lack ofknowledge about austral-opithecines and'Mrs Ples', many respond-ents in the metropolitan sample havevisited Sterkfontein (317o), and the major-ity had visited a museum (80%), includingthe Transvaal Museum (677o).

In a separate study in January 1997, vis-itors to the Transvaal Museum were askedthe same set of questions. Sixty-five percent of the respondents indicated that theywere aware of 'Mrs Ples' after they hadgone through the 'Genesis II' hall f'eatur-ing exhibitions of australopithecines.

Recent effbrts to promote an awarenessof 'Mrs Ples' through publicity in newspa-pers, a Youthlink programme (Ecolirrk'97) run at the Transvaal Museum, and

J.F. Thackeray is in the Department of Palaeon-

tology and Palaeoenvironmental Studies,

Transvaal Museum; Kathryn Mathers is in the

Department of Anthropology and Archaeology,

University of South Africa.