Late Pleistocene coastal environment of the Southern Cape Province of South Africa: Micromammals from klasies river mouth

Journal of Archaeological Science 1987,14,405-421

Late Pleistocene Coastal Environment of the Southern Cape Province of South Africa: Micromammals from Klkies River Mouth

D. M. Avery’

(Received 19 August 1986, revised manuscript accepted8 December 1986)

A sequence of samples of micromammalian remains from Klasies River Mouth on the south coast of South Africa provides evidence of vegetational and climatic change during the Late Pleistocene. The evidence suggests the presence of a vegetational mosaic similar to that of the present but with relatively more open vegetation at the time the central part of the sequence was being deposited than was the case at the beginning or the end. Fluctuations occurred in general climatic conditions, as indicated by the Shannon-Wiener index of diversity, but conditions appear to have remained relatively moderate throughout with no evidence of glacial or interglacial maxima. Changes in sea level are probably also reflected in changed proportions of various species of small mammal. The site has yet to be dated conclusively but the micromammalian data te.nJd to support other lines of evidence which suggest that this sequence of deposits was laid down during isotope stage 5, probably substages 5d-a. Human response to the challenge of changing conditions can be shown to lag behind those changes as recorded by micromammals.

Keywords: CLIMATE, DATING, HUMAN ADAPTATION, KLASIES RIVER MOUTH, MICROMAMMALS, SEA LEVEL, SOUTH AFRICA, LATE PLEIS- TOCENE, VEGETATION.

Introduction The Klasies River Mouth (KRM) sites have been of prime importance in increasing the known or anticipated antiquity of both Homo sapiens sapiens and Middle Stone Age (MSA) technology during the Late Pleistocene in southern Africa. Remains of H. s. sapiens from these sites are among the oldest in Africa (Rightmire, 1984: 164) and are claimed to be the earliest directly associated with MSA material (Singer & Wymer, 1982: 148). The sites have provided a relative chronological framework for the MSA in southernmost Africa (Volman, 1984: 195) as well as a large part of the typological framework, with examples of all sections of Volman’s (1984: 201) informal culture- stratigraphic sequence except his earliest division, termed MSA 1. The subsistence strategies of the MSA people have also been examined (Klein, 1976; Singer & Wymer, 1982; Voigt, 1982; Binford, 1984), with some emphasis being placed on the central

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406 D. M. AVERY

location of the site in a highly varied environment and “the successful interaction between the populations and the environment” (Singer & Wymer, 1982: 107).

The original excavations were undertaken in 1967-8 with a view to solving some of the problems concerning human physical and cultural evolution in South Africa (Singer 8z Wymer, 1982: 7). Subsequent excavations, on which this report is based, were undertaken by H. J. Deacon in 1984-6 in an attempt to improve understanding of the effects of climatic change on the distribution and relative abundance of human populations during the Late Pleistocene (Deacon et a/., 1986) by obtaining much more detailed information on environmental change during the Last Interglacial-Last Glacial cycle. It was also necessary to address once more the problem of a lack of secure dating for the sequence, which various workers (Butzer, 1978; Shackleton, 1982; Singer & Wymer, 1982; Hendey & Volman, 1986) have attempted to solve. Another reason for the re-excavation was to acquire an improved suite of samples of micromammals, because the contemporary micromammalian remains provide unique information for any assessment of the role of environment in effecting change in human cultural/technological development. Micromammalian remains were known to exist in the deposits (Singer & Wymer, 1982; pers. obs.) but had not been collected in such a way as to allow detailed quantitative analysis (Avery, 1982a). A preliminary account of the top part of the new series of micromammalian samples has been published (Avery, 1986a); the present account deals with the whole series and assesses its contribution to the overall information available from the site.

The Modern Environment The material to be discussed was recovered from Klasies River Mouth 1A (KRM lA), which is one of a complex of sites located at 34”06’S 24”24’E on the south coast of the Cape Province (Figure 1) some 40 km west of Cape St Francis. The site is situated some 6-8 m above sea level at the base of cliffs that rise steeply some 60-100 m to the coastal plain above (Butzer, 1978). On the landward side of the plain, which is approximately 10 km wide at this point, lies a mountain range with an average elevation of some 600 m. The coastal plain is incised by several rivers, including the small Klasies River which joins the sea via a steep-sided valley approximately 1 km west of the site. In addition, numerous springs emerge from below the calcreted dunes that top the cliffs in the vicinity of the site (Singer & Wymer, 1982: 2).

Klasies River Mouth is located towards the eastern limit of the fynbos (= macchia) biome (Huntley, 1984). In the immediate vicinity of the site on a substrate of neutral to alkaline recent sands, the vegetation comprises a mosaic of Dune Fynbos (mid-dense to closed mid-high shrubland) and Kaffrarian Thicket (closed shrubland to low forest) (Moll et al., 1984; 1: 1 ,OOO,OOO map of the vegetation of the Fynbos Biome, 1983). Dune Fynbos includes a strong component of large-leaved dorsiventral-leaved shrubs and although the grass cover can be quite high, especially in seasonally waterlogged dune valleys, restioids and small-leaved shrubs dominate the herb and shrub strata, respectively, on well-drained sites (Cowling, 1984: 201). Dune Fynbos tends to occur on shallower soils than the Kaffrarian Thicket which is dominated by evergreen sclerophyllous trees and shrubs with a high cover of stem spines and vines (Cowling, 1984: 213). Further inland on the more acid soils of the coastal foreland, the land has been extensively cultivated but there occur remnants of South Coast Renosterveld which comprises open to mid-dense small-leaved shrubs with a relatively high proportion of grasses in the understory (Mall et al., 1984) as well as Mesic Grassy Fynbos, a grassy heathland. The general picture gained by extrapo- lation from Cowling’s (1984) work is that there would have been thicket in well-drained positions with relatively more fertile soils, fynbos shrubland on less fertile, well-drained soils and graminoids, whether grass or restoids, in seasonally waterlogged positions. It is

LATE PLEISTOCENE COASTAL ENVIRONMENT 407

I L +-+

‘35”

Figure 1. Location of Klasies River Mouth and other sites mentioned in the text. BNK, Byneskranskop; BP, Boomplaas; DK, Die Kelders; GT, Glentyre; KRM, Klasies River Mouth; NBC, Nelson Bay Cave.

conceivable that Knysna Afromontane Forest, which today is found no closer than some 20 km to the west of KRM, may have extended further eastwards along the coastal platform during the past, but this would presuppose an annual rainfall in excess of 800 mm falling very evenly throughout the year.

One of the most notable aspects of the vegetation in the region is its mixed affinities and transitional nature. Dune Fynbos comprises a mosaic of Cape fynbos shrublands and subtropical elements: Kaffrarian Thicket is a subtropical transitional thicket with strong Afromontane forest affinities; South Coast Renosterveld has Cape/Karoo-Namib/ Sudano-Zambesian affinities; Mesic Grassy Fynbos has a high proportion of Cape- Afromontane linking species and widely distributed tropical C,-grasses (Moll et al., 1984). Given the balance implied by this situation, it is likely that a relatively small change in climate would alter the vegetation pattern considerably.

The climate of the region is characterized by its equability. In general terms, the rainfall is year-round (Schulze, 1984: 287). It is also highly reliable and shows low variability (Weather Bureau, 1957). There is, however, as Butzer (1978) pointed out, a fairly steep east-west rainfall gradient in the vicinity of KRM which is itself situated between the 800 and 1000 mm isohyets, with nearby weather stations returning long-term averages of approximately 950 mm (Weather Bureau, 1954). Some 40 km to the east, the average is about 700 mm, whereas it is about 1100 mm the same distance to the west. The overall pattern is exemplified by the 1976 data (Weather Bureau, 1981) for Storms River Mouth and Cape St Francis, which lie 30’ west and 26’ east of KRM, respectively. Storms River Mouth received 1160.5 mm of rain over a total of 103 d, while Cape St Francis received

408 D. M. AVERY

885.1 mm over 111 d. Temperature also shows relatively little diurnal or seasonal variation, and frost is practically unknown (Schulze, 1984: 314). The range between mean daily maxima and minima is about 7°C with a similar difference between hottest and coldest months. For Storms River Mouth the range in average monthly maxima and minima is 23.7/16*6”C in February to 17*8/9.8”C in July and for Cape St Francis it is 23*2/18O”C in December to 17.5/10.7”C in July (Weather Bureau, 1981).

A generalized correlation can be made between vegetation categories and rainfall which will serve as a basis for interpreting the data from KRM. Several points can be made about the base data given in Table 3. Firstly, the long-term average rainfall in Dune Fynbos is approximately half that in Kaffrarian Thicket for the stations used to represent the current main areas of distribution of the vegetation categories. It must be emphasized, however, that there is a certain amount of variation, and Cowling (1984: 193) gives rainfall ranges in the Humansdorp area (Figure 1) of 300-800 mm for Dune Fynbos and 500-750 mm for Kaffrarian Thicket. The intermediate figure returned for the ecotonal station confirms the overlap, although it would appear that optimal rainfall for Kaffrarian Thicket is probably at least 200mm higher than it is for Dune Fynbos. Another limiting factor is the season in which the rain is received. Moll et al. (1984) stated that Kaffrarian Thicket occurs in areas where at least 30% of the rainfall is received during winter, a coincidence that is supported by the data in Table 3; even at the western extremity of the Dune Fynbos/Kaffrarian Thicket mosaic, where the rainfall average is only 417 mm, 29% was received in winter 1976. South Coast Renosterveld is also said to be found in areas receiving 30% of the annual 300600 mm rainfall during the winter. In the Dune Fynbos, on the other hand, there appear to be peaks in spring and autumn. Of the two remaining vegetation categories, Mesic Grassy Fynbos occurs in areas with an average rainfall of 600-900 mm (Moll et al., 1984), whereas Afromontane Forest occurs in areas of > 800 mm rainfall (Cowling, 1984: 193). In both cases there is an indication of a spring peak, although there tends to be less seasonal variation in the forest.

Materials and Methods Detailed description of the 1984-6 excavations is under way (H. J. Deacon, in preparation). In general, however, the basic strategy was to sample the sequence by excavating a column of up to 1 m2 through the deposits which are more than 15 m thick and comprise a series of sands intercalated with human occupation horizons (Deacon et al., 1986). Because of the depth of deposit and steep slope, the original excavations were conducted in a step trench with various side additions (Singer & Wymer, 1982) which, in turn, made it necessary to excavate the later sequence of samples from different squares at different depths. In general, however, the squares are in alphabetical order from the top to the bottom of the sequence (Table I), with C56 at the top and T50 at the base in KRM lA, followed by square AA43 (assignable to KRM 1 which adjoins KRM 1A at the base of the latter). There is some doubt as to the exact position of square 050 in the sequence, because of the complexities of the stratigraphy, but it is provisionally placed above T50. The excavators intend to omit squares M50 (DM-RL), N51 and Q52 (i.e. samples 32,34,35 in this study) from consideration in their report because of uncertainty of precise stratigraphic location (V.B. Geleijnse, pers. comm.). The samples from these deposits have, however, been retained in the present paper because they do not give anomalous results; neither would their omission alter the conclusions reached, so there is some reason for suggesting that, in fact, they have been correctly placed in the sequence. The samples from square C56 are separated from those in square E50 by deposits representing an unknown period of time, a fact that must be borne in mind when the data are interpreted.

The material on which the analysis was based comprises the mandibles and maxillae of rodents and insectivores recovered from excavated samples (see Tables 1 and 2). Remains


Table 1. List of samples from Klasies River Mouth in stratigraphic sequence, the youngest at the top, with sample size (N), number of species (s), and values of general diversity with (H) and without (H*) Otomys irroratus (Industrial associations given below)

Sample Excavation no. Square unit N s H H*

8 9

10 11 12 13 14 15 16 17 18 19 2Q.- 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41

C56

E50

H51

J51

K48 M50

N51 452

050 T50

AA43

Top/mid Base

CPTSAT AU AV AB BSL CP2 BSSl BSS2 CP3

BSS3/4 CP4 BSSS BS

YSl YS2 YS3 YS4

CPb14 CP15-17 C18+ CPl-3

CP4YS5 CPbYS7 CP11/12

YSxlbCPx5 YSx4 YSXS All

DM-RL YSSM2

All CSHGA

HGEHGCa ss All BS4

BS4L/SM All All

214 15 2.06 2.07 216 12 1.94 1.93 359 19 2.30 2.27 376 16 2.17 2.16 217 16 2.27 2.24 352 15 2.18 2.10 269 17 2.24 2.20 363 14 2.16 2.12 133 14 2.20 2.20 266 15 2.18 2.11 471 14 2.14 2.06 110 14 2.22 2.12 721 16 2.09 2.11 415 14 2.07 1.99 630 15 2.01 1.98 201 12 1.95 190 418 17 2.05 2.06 549 14 2.01 1.98

1074 16 2.03 2.10 146 14 2.07 2.02 133 11 2.12 2.08 108 12 2.26 2.18 218 13 2.08 2.14 185 15 2.18 2.24 109 11 2.11 2.08 153 12 2.13 2.12 122 16 2.21 2.23 167 13 2.12 2.08 206 14 2.21 2.14 606 17 2.10 2.10 115 14 2.13 2.14 266 14 2.15 2.12 456 17 2.17 2.20 117 14 2.14 2.12 200 14 2.18 2.17 170 16 2.22 2.28 192 14 1.97 1.95 46 12 1.96 1.97

126 13 1.94 1.97 126 12 1.92 2.07 51 12 2.14 2.07

Industrial associations: Samples l-2, none; 3-19, MSA III; 2lk30, Howieson’s Poort: 3140, MSA II; 41, MSA 1.

of bats, of which there were very few, were also identified but not otherwise considered in the interpretations. It is considered most likely that the skeletons represent the remains of decomposed pellets regurgitated at the site by owls. The reasoning behind this has been discussed previously (Avery, 1982a: 207) when it was concluded that the barn owl Tyto alba was the probable species involved. The owls may well have roosted in the shelter when

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Table 2. Species represented in the samples, with number of samples(N) in whicheach occurs and range (max. % and min. 5%) of percentage representation in the micromammalian assemblage

Species Common name N Max. % Min. %

Amblysomus hottentotus Hottentot golden mole Chlorotalpa duthiae Duthie’s golden mole Macroscelides proboscideus Round-eared elephant shrew Crocidura cyanea Reddish-grey musk shrew Crociduraflavescens Greater musk shrew Myosorex varius Forest shrew Suncus infinitesimus Least dwarf shrew Mystromys albicaudatus White-tailed mouse Dendromus melanotis Grey climbing mouse Dendromus mesomelas Brants’ climbing mouse Acomys subspinosus Cape spiny mouse Dasymys incomtus Water rat Mus minutoides Pygmy mouse Praomys verreauxii Verreaux’s mouse Rhabdomyspumilio Striped mouse Thallomys paedulcus Tree mouse Thamnomys dolichurus Woodland mouse Otomys irroratus Vlei rat Otomys laminatus Laminate vlei rat Otomys saundersiae Saunders’ vlei rat Graphiurus ocularis Spectacled dormouse Cryptomys hottentotus Common mole rat Georychus capensis Cape mole rat

4 10.00 0.00 41 6.82 1.37

41 41 11 23 24 23

7 36 22 25 41

41 41 41

2 40 41

0.82 0.17

15.22 4.26 19.61 3.98 1.08 0.00 2.17 OXKI 2.35. OOI 2.46 040 1.11 0.00 2.79 040 2.17 0.00 2.79 0.00

25.07 4.63 0.24 1.39

39.68 15.45 18.42 2.17 26.27 6.14 0.75 0.37 4.00 040 4.58 0.83

people were not in occupation, although it is possible that both groups could have used the site at the same time since barn owls are today often found in or near human habitation (Steyn, 1982: 241). The present samples contain a relatively high proportion of striped mouse Rhabdomys pumilio (Table 2), which is predominantly diurnal (Smithers, 1983: 238), whereas the barn owl normally only begins hunting at dusk (Steyn, 1982: 241). The activity peaks of the marsh owl Asio cape&s coincide with those of R. pumilio, and this owl has been recorded as taking a higher proportion of R. pumilio (Dean, 1977) but it roosts in grassland not on rocky ledges. The most likely explanation, therefore, remains that the material accumulated as a result of barn owl activity. The high proportions of R. pumilio may perhaps be attributed to the presence of large numbers of this species, particularly in the vicinity of the site, or even to a relatively high incidence of dull, cloudy days since barn owls have been observed to hunt on such days (McLachlan & Liversidge, 1970: 247).

Minimum numbers of individuals were derived from the highest number of any one jaw, with the jaws only being counted if they include a predetermined, frequently preserved element, which varied from one species to another. Inevitably, breakage will cause some problems in identification, but the point has already been made (Avery, 1986a) that in the present case errors at the specific level are unlikely to affect interpretation. Minimum numbers of individuals were initially calculated for each excavation unit, although samples from individual excavation units within one square were grouped subsequently in some cases to raise the number of individuals (iV) to over 100 in each sample. In two cases near the base of the sequence the total for a square was below 100; for squares 050 and AA43 N was 46 and 5 1, respectively. In all, 41 samples were examined, as listed in Table 1, which also gives sample size in each case.


401 I

20

(a)

(b)

51122334 51122334 0505050 0505050

Samples

Figure 2. Variation in representation of various species indicative of open vegetation, expressed as a percentage of the total micromammalian fauna. Note different vertical scale for Otomys saunakrsiae. See Table 1 for details of samples 141. (a) Otomys saundersiae; (b) Chlorotalpa duthiae; (c) Amblysomus hottentotus; (d) Cryptomys hottentotus; (e) Georychus capensis.

At this stage the material has been examined from three points of view before some comments are made on the possible effects of inferred environmental change on human subsistence. Firstly, variation in the proportion of various species (Figures 2 and 3) is interpreted in terms of the vegetation in the section of the landscape of which they are representative. Not all species can be used for this purpose, either because they are too catholic in their habitat requirements or because too little is known about them. However, as many as possible have been included to increasethe confidence of the interpretations. Basic ecological data have been taken from Smithers (1983), as well as from other authors cited in Avery (1982~). Changes in climatic seasonality and sea level have also to be taken into account to explain variation in proportions that would be unexpected if only vegetation were changing.

The second aspect to be examined is the structure of the micromammalian community, comprising the number of species and their proportional representation in the community. There is convincing evidence (Avery, 1982aJ.1, 1986b) that the Shannon-Wiener

412 D. M. AVERY

i22jj4 0505050

Samples

Figure 3. Variation in representation of various species indicative of closed vegetation, expressed as a percentage of the total micromammalian fauna. Note different vertical scale for Otomys irroratus. See Table 1 for details of samples l-41. (a) Otomys irroratus; (b) Rhabdomys pumilio; (c) Otomys laminatus; (d) Mysorex varius; (e) Crociduraflavescens.

index of general diversity, and to a lesser extent its components of dominance and species richness, provide a good indication of changing climatic conditions. The number and proportional representation of species in the community can both vary with climatic conditions, but it is necessary here to point out that the evidence from the indices is relative and non-specific. In other words, higher values of the Shannon-Wiener index, H= -X(P, logePi) (Ricklefs, 1980), may indicate more equable conditions but the precise nature of those conditions has to be determined by other methods. Because Otomys irroratus is the best represented species and will therefore have a major effect on patterns of change reflected in the samples, values of H were also calculated with 0. irrorutus omitted from the samples (Table 1; Figure 4).

Lastly, the contribution of the micromammalian ‘data to the relative dating of the sequence is discussed. Patterns of variation in values of the Shannon-Weiner index and proportional representation of certain species can be compared with the patterns from


5e

2.4 (a) I

Samples Figure 4. Variation in values of the Shannon-Weiner index with (a) and without (b) Otomys irrorafus, compared with change in oxygen isotope composition of plank- tonic foramenifera in core RCl l-120 (after Shackleton, 1982). 5e-5a, Oxygen isotope substages.

other sites. Taking these into account with what is known from other lines of evidence it is possible to suggest an approximate age for the deposits. Because this is not a precise method, it is only worth using as corroborative evidence when absolute dates are not available.

Vegetation Results and Discussion

The species can be divided into those that represent more open vegetation (Figure 2) and those that are indicative of more closed vegetation (Figure 3). Within the former group, Saunders’ vlei rat Otomys saundersiae suggests drier graminoid, possibly restioid, vegetation on the rocky slopes on the seaward edge of the landscape. On the flats behind, the

414 D. M. AVERY

Hottentot golden mole Amblysomus hottentotus and the mole rats Cryptomys hottentotus and Georychus capensis indicate grass and probably geophytes, respectively. Chlorotalpa duthiae occurs in alluvial sand and sandy loam (Smithers, 1983: 29), probably under conditions similar to those suitable for A. hottentotus. Although C. hottentotus is extremely widely distributed (Smithers, 1983), Davies & Jarvis (1986) have recorded for the southwestern Cape Province that this species relies heavily on geophytes for both food and nesting material. It is also possible that G. capensis may be taken as indicating geophytes. Its distribution is essentially confined to the fynbos biome, of which geophytes are a feature (Kruger, 1979), and it subsists largely on bulbs, roots and tubers (Smithers, 1983: 184).

A. hottentotus shows a positive correlation with 0. saundersiae but a negative correlation with the mole rats (Table 4), and it is noticeable that, whereas the graminoid- indicator species reach a peak in samples 20-10 approximately, there is a decline in the proportion of mole rats at that time. In terms of the vegetation categories in the region today it is most likely that 0. saundersiae and A. hottentotus indicate periodic expansion of the Dune Fynbos, with 0. saundersiae on well-drained slopes with fynbos shrubs and restioids and A. hottentotus in the grassland of the seasonally waterlogged flats. Since the distribution of C. duthiae coincides roughly with that of the Dune Fynbos/Kaffrarian Thicket ecotone, and proportions of this species show a significant positive correlation with those of A. hottentotus, it probably represents similar conditions to those indicated by A. hottentotus. It is also possible that,both species occurred further inland where the Dune Fynbos was replaced by Mesic Grassy Fynbos. The mole rats, on the other hand, could represent an increase in South Coast Renosterveld in which geophytes are a prominent feature.

Closed vegetation, in particular a dense understorey of graminoid herbs, is indicated by the striped mouse R. pumilio on the flats and by the laminate vlei rat Otomys laminatus on the rocky slopes (Figure 3). These species both vary inversely with A. hottentotus and 0. saundersiae (Table 4), showing a fairly clear pattern of denser vegetation in the earlier and later samples relative to the middle samples from about 20 to 10 on both the hillsides and the flats. Further support for this basic pattern appears to be provided by other species that occur in small numbers. On the rocky slopes, at the edge of thicket or forest, Verreaux’s mouse Praomys verreauxii and the Cape spiny mouse Acomys subspinosus and on the flatter areas the climbing mice Dendromus melanotis and D. mesomelas indicate a decline in denser herbaceous vegetation in the middle period. It seems likely that during the periods of denser vegetation, and particularly near the top of the sequence, there was an increase in Kaffrarian Thicket relative to Dune Fynbos; Mesic Grassy Fynbos probably also became more closed. There is no need to invoke major changes in the vegetation during the Late Pleistocene to explain the observed differences which appear to be more in the nature of variation in quality and proportion relative to those of the present day.

The indication that there was denser vegetation at the beginning of the KRM IA sequence is in general agreement with Klein’s (1976) interpretation of the large mammal fauna. Unfortunately, the constraints of small samples forced him to group samples on the basis of the cultural content of the levels, thereby masking any change caused by other agencies. It appears, however, that the more open vegetation suggested by Klein (1976) for the time of the Howieson’s Poort levels is matched in a general way by the central portion of the new sequence of micromammalian samples discussed here. Thereafter, Klein (1976) maintained that the vegetation again became more closed, as is postulated here. There is thus very good general agreement between the two lines of evidence.

One species deserves separate discussion and that is the vlei rat 0. irroratus. This is the dominant species in all samples except three where there is a slightly greater number of 0. saundersiae, and it never constitutes less than 15% of any sample, in one case rising to


40% (Table 2; Figure 3). This latter figure is approaching the 53% recorded (Avery, 1982~) for a modem sample from Glentyre, some 200 km west of KRM (Figure 1). The environment of Glentyre comprises a string of reed-fringed lakes separated from the sea by a dune cordon, supporting ecotonal Dune Fynbos/Kaffrarian Thicket and flanked on the landward side by temperate Knysna Afromontane Forest. It is possible that during the Last Interglacial, Afromontane Forest may have extended further eastwards along the mountains than it does today, while in the vicinity of KRM it is probable that the ecological equivalent of the reed element at Glentyre was the seasonally waterlogged grassland component of Dune Fynbos and/or Mesic Grassy Fynbos. One of the differen- tiating characteristics of Grassy Fynbos is the presence of nanophylls (plants with leaves 25-225 m*; Campbell et al., 1981), and Bond et al. (1980) found that the distribution of 0. irroratus was correlated with microphyllous plants and, in particular, with >75% shrub cover.

0. irroratus, however, exhibits a different pattern from all other species (Figure 3). It is not positively correlated with any other species (Table 4) and is the only species to be relatively highly represented in both the earliest samples and those between about 20 and 13. As an inhabitant of lush herbaceous vegetation, 0. irroratus might have been expected to decline during this latter period. Equally, one might have predicted that it would increase in the later samples, whereas the reverse is the case. It is very possible that the explanation lies in the fact that, like Myosorex varius, 0. irroratus may well have occurred on the slopes as well as on the flats. Beyond this, it is possible that changes in seasonality of weather and the sea level also affected this species as is discussed below.

Climatic conditions There are very clear fluctuations in the value of H, the Shannon-Wiener general diversity index (Figure 4; Table l), and Figure 4 shows that, in fact, the pattern of variation in values of H is very similar, regardless of whether or not 0. irrorutus is included in the calculations so that, although proportions of this species appear to vary inversely with values of H, they are not distorting this index to any extent. There are two major troughs (represented by samples 13-20 and 3740) and two major peaks (represented by samples 3-12 and 21-36). In addition, the two uppermost samples appear to indicate the begin- nings of an upswing from another trough that is not represented in the present series of samples, and the lowest sample indicates part of another peak that is not wholly represented and whose downslope may be lost in a hiatus. The values of the index Hlie between 1.9 and 2.3, with the majority being below 2.2. This latter value has been shown (Avery, 1986b) to be a fairly consistent cut-off between Holocene interglacial scores and Late Pleistocene glacial scores in South Africa. The values are intermediate, and it seems very likely that conditions throughout the period of occupation represented by the samples were generally moderate, although fluctuating to some extent.

It must also be noted that a positive correlation between R.pumilio and the mole rats, G. cupensis and C. hottentotus (Table 4), may possibly indicate a more marked seasonality in the rainfall at certain periods. Reproduction in R. pumilio, which occurs in summer, is correlated positively (Perrin, 1980) and negatively (David & Jarvis, 1985) with rainfall in different parts of the country. G. cupensis also has a summer breeding season (Taylor et al., 1985), at least in the southwestern Cape Province which is a winter-rainfall region. Moreover, R. pumilio has been characterized (Perrin, 1980) as a generalized opportunistic omnivore whose trophic strategy is to exploit transient foods such as seeds and/or insects. The mole rats cache food and subsist largely on geophytes (Davies 8c Jarvis, 1985), presumably as a means of dealing with seasonal shortages of food. If, in fact, the mole rats are connected with South Coast Renosterveld and R.pumilio with Kaffrarian Thicket, this

416 D. M. AVERY

Table 3. Rainfall datafor stations in various vegetation types

Vegetation Station Coordinates LTA (mm)* % per seasont

Dune Fynbos Dune Fynbos/Kaffrarian

Thicket mosaic Kaffrarian Thicket South Coast Renosterveld Mesic Grassy Fynbos Afromontane Forest

Stillbay 342212125 432 12-36-22-31

Cape St Francis 341212450 664 11-29-34-26 The Island 335912522 891 U-27-30-27

Humansdorp 340212446 699 09-36-29-27 Suuranys 335312417 640 2619-23-32

Bloukrans 335712338 1004 22-21-1940

*LTA, long-term average. tFor 1976 except Stillbay (1974). Seasons are in the order summer (December- February), autumn (March-May), winter (June-August) and spring (September- November).

could indicate a relative increase in winter rainfall and a concomitant decrease in summer rainfall (Table 3), thereby supporting the hypothesis of enhanced seasonality at certain times during the past.

Conversely, the negative correlation of 0. irroratus with the other three species (Table 4) suggests that at other times rainfall was more evenly distributed throughout the year. 0. irroratus is a specialized herbivore that relies on a stable and abundant food supply year- round, and its breeding strategy suggests that it is adapted to coping with irregular rather than seasonal ( = regular/predictable) rainfall (Perrin, 1980). This does not suggest that 0. irroratus is absent from areas with a seasonal climate but that it will be restricted to a constant microhabitat such as riverine vegetation and maintain a basic population level. On the other hand, when conditions are more widely favourable to the specialist it will have a clear advantage over the generalist, as was indicated by Brooks (1974). From this it can be inferred that at certain times at KRM, represented notably near the base of the sequence (Figure 3), the climate (and perhaps specifically effective precipitation) was much less seasonal that at other times. Again, this indication is in line with the general picture suggested for the vegetation since both Mesic Grassy Fynbos and Afromontane Forest tend to receive rainfall more evenly throughout the year, although with a spring peak. In general, however, there is every reason to believe that total rainfall in the vicinity of the site remained within a range of approximately 500-800 mm per annum; the lower limit is set by the presence throughout of A. hottentotus which today is restricted to areas receiving over 500 mm (Smithers 1983: 35), and the upper limit by a representative annual rainfall in the Kaffrarian Thicket today (Table 3).

Sea-level changes There is another group of species which shows a different pattern of change. These species all indicate closed vegetation, yet two of them, the shrews M. varius and Crocidura fravescens, tend to exhibit a general reduction towards the top of the sequence (Figure 3), whereas the water rat Dasymys incomtus increases towards the top. This is reflected in a negative correlation between the latter and the two former species which are in turn positively correlated with each other (Table 4). It is suggested that the explanation for this different pattern lies in sea-level changes. If C.jlavescens occurred principally on the lower slopes, rising sea level at the time the upper levels were being deposited would reduce the habitat available for this species, thereby preventing the increase in its numbers that might have been expected on other grounds. The same may be true for M. vurius. It has already


Table 4. Kendall rank correlation coeficienis based on percentages of the better represented species at Klasies River Mouth IA

AHOT CDUT CFLA MVAR DINC RPUM OIRR OLAM OSAU CHOT

CDUT 0944 CFLA -0.118 -0440 MVAR 0.007 0.002 0.277 DINC 0.142 0.102 -0.316 -0.232 RPUM -0.244 0.037 -0.110 -0.154 0905 OIRR -0.156 -0.291 -0.111 -0.128 -0.077 -0.185 OLAM -0-300 -0.088 -0.015 0.024 0.106 0.066 -0.159 OSAU 0444 0.154 -0.257 -0.251 0.112 -0.263 -0.049 -&227 CHOT -0.195 0.117 0.147 -0.002 0.074 @l% -0266 -0.017 -0m5 GCAP -@195 0.105 0.136 0.002 0.045 0.230 -0.266 -0.022 -0.210 0.936

Species are: AHOT, Amblysomus hottentotus: CDUT, Chrysochloris duthiae; CFLA, Crociduraflaveseens; MVAR, Myosorex varius: DINC, Darymys incomtus; RPUM, Rhabdomyspumilio: OIRR, Otomys irroratus; OLAM, Otomys laminatus; OSAU, Otomys sawuiersiae; CHOT, Cryptomys hottentotus; GCAP, Georychus capensis. Values indicating significance at the 0.05 level or below are in bold type.

been noted (Avery, 1982a) that M. varius is likely to be found on hillsides as well as flats, so that in this case, if it occurred below the site as well as above it, rising sea level would also have contributed to the continued decline of this species. The converse pattern in D. incomtus could be explained by a change in the gradient of the river caused by variation in the sea level. In this case, a lower sea level at the beginning of the sequence would cause a steeper down-cutting gradient to the river which, in turn, would entail steeper river banks and consequently a reduced habitat for D. incomtus. The situation would be reversed by a higher sea level.

Butzer (1978) suggested that the sea level was high at the time the upper levels in KRM 1A were deposited, which would agree with the interpretation proposed here. It need not have risen above its present level, as suggested by Butzer (1978) but rejected by Hendey & Volman (1986), but if it were higher than previously this might explain the evidence. In this context, the major sea-level surge at about 95,000 bp proposed by Hollin (1980) could have some bearing on the matter, even if one accepts the most conservative estimate of a rise to - 2 m rather than the possible + 16 m.

Relative dating Variation in the values of H for different samples can provide an indication of the relative dating of sites such as KRM that have no available satisfactory absolute dates. There are unfortunately no known Last Interglacial samples available to test the hypothesis that scores for these would have been comparable to those for the Holocene (Avery, 1982~) but there is no reason to suppose otherwise. Low values are recorded (Avery, 1982a) for the last gIacia1 maximum + 18,000 bp at Boomplaas (1.69-1.79) (Figure 1) and Nelson Bay Cave (l-51 and 1.62) both in the southern Cape Province. Although Nelson Bay Cave is currently on the coast, it would have been some 80 km inland during the last glacial maximum (Dingle & Rogers, 1972) and thus an inland site. The values for KRM 1A are intermediate. They are similar to those recorded for isotope stage 5a, about 80,000 bp, and stage 3, about 60,000 bp, at Boomplaas and, by implication, Die Kelders. Values for the two topmost samples, which are separated from the main sequence, are among the lowest

418 D. M. AVERY

and could represent part of the recovery from stages 4 or 2. If the whole sequence is taken into account, it is perhaps most likely that the main body of samples represents the end of substages 5e up to 5a. Stage 4 is probably not represented in the sequence because one would expect a more obvious difference between the low values if stages 4 and 5b were represented rather than stages 5b and 5d.

The suggested correlation of the H values with the oxygen isotope curve, based on core RCl l-l 20 from the south Indian Ocean as redrawn by Shackleton (1982) from Hays et al. (1976) is shown in Figure 4. There is good correspondence between the two, although the terrestrial curve should probably be offset from the marine curve because there would be a lag in response first by the vegetation and then by the mammals to changing conditions. Another core, RC 17769 from 500 km southeast of Durban, shows very clearly, both in the original interpretation (Be & Duplessy, 1976) and in the reinterpretation (Prell etal., 1979) that stage 3 was more clearly comparable to stages 4 and 2 and therefore essentially glacial rather than interglacial. This would reinforce the view expressed here that the deposits under discussion were laid down during stage 5 and, except perhaps for levels 1 and 2, not during stages 3 and/or 4.

Hendey & Volman (1986) concluded that occupation probably began during isotope substage 5e but that it is perhaps only safe to say that the MSA occupation of KRM was largely, or entirely, confined to isotope stage 5. The present evidence does not contradict this conservative interpretation. Neither does it disagree with the previous interpretations of Butzer (1978) and Klein (1983) that the top of the KRM 1A sequence is equated with substage 5a. Both, however, infer that the base of the KRM 1A sequence falls within substage 5c, and Shackleton (1982) suggests that an apparently slightly earlier sample from KRM Cave 1 (KRM 1) could be assigned to either 5a or 5c. There may be some mis- correlation caused by the use of different types of evidence, as well as possible stratigraphic problems at the base of the sequence, which could account for the apparent discrepancy but, apart from that, agreement in interpretation of the various lines of evidence is generally good.

Implications for human subsistence A detailed investigation of the implications of changes in the environment for human subsistence strategies is beyond the scope of this paper and will, in any case, be more appropriate when analysis of the new artifactual material has been completed by H. J. Deacon and co-workers, but a few comments are in order. As a basis for discussion, it can be stated that samples 3-19 came from levels yielding MSA III material (see Singer & Wymer, 1982, for details of the industries), samples 20-30 were from levels containing Howieson’s Poort material, samples 3 l-40 from levels with MSA II, and finally sample 41 was from a level with MSA 1 material. Singer & Wymer (1982: 112) suggest that the great difference between the Howieson’s Poort and other MSA industries probably reflects the adoption of new hunting techniques. They further suggest (1982: 209) that these new methods may have been devised to catch smaller, faster game but, in fact, the only species to occur in relatively higher proportions in the Howieson’s Poort samples than in the earlier samples were Cape buffalo Syncerus ca&r and quagga Equus quugga (using figures given in Klein, 1976). The emphasis was certainly not on small game, although it may have been on faster game in the form of quagga. There was, however, a greater diversity of terrestrial game represented in the Howieson’s Poort samples than was previously the case, and even in the later MSA III samples the figure was again lower; diversity (d= s - l/ log,N, where s is the number of species and N is the total of individuals) is 4.42 in the combined Howieson’s Poort samples versus 2.47 in the MSA II samples and 3.96 in the MSA III samples, again using figures given in Klein (1976), which may indicate a change


in emphasis from marine resources towards terrestrial resources. This is not to imply that marine foods were ignored but it does seem possible that a progressive increase in variety of available land game (suggested by a major increase in general diversity in small mammals some time before the MSA II was replaced by the Howieson’s Poort industry) may have provided the impetus for people to develop, introduce or adapt the tools with which to take advantage of the situation. This suggestion is perhaps further supported by the fact that the Howieson’s Poort industries are widely distributed at inland sites (Volman, 1984) which indicates that they cannot have been marine-orientated.

On the basis of changing values of the Shannon index (Figure 4), there also appears to have been a change in climatic conditions in progress for some time before the MSA III industry was introduced, and such a lag in adapting to changes should be anticipated. As an example, it is reasonable to suppose that quagga had been in the neighbourhood for some time before they appeared, along with Howieson’s Poort tools, among the food refuse of the people living at Klasies River, and that the people would have taken some time to respond to the challenge of a new source of food. Because the micromammals can be expected to react more quickly to environmental change (see Avery, 1982a, for a discussion of this point) than large mammals, one could expect that the latter may have arrived in the area at some time between the change shown by the small mammals and their appearance in the site. A more detailed examination of this kind of data could well aid understanding of human adaptation to changing environments and, in particular, the extent to which early H. s. sapiens was capable of maximizing the opportunities afforded by such changes.

Conclusions The micromammalian evidence agrees broadly with that from other data. Against a background of generally moderate, though fluctuating, climatic conditions, vegetation alternated from being relatively closed to more open and back to closed, which agrees with Klein’s (1976) interpretation. Thicket and fynbos shrubs probably became alternately more or less extensive in the better drained locations, while graminoids occurred in seasonally waterlogged locations which might’be expected to be more or less extensive and dense, depending on annual rainfall. Superimposed upon this pattern is an indication of rising sea level towards the top of the sequence which may provide support for the theory of sea-level surges proposed by Hollin (1980) and is in accordance with Butzer’s (1978) suggestion based on the geomorphology of KRM sites. Relative dating of the sequence by comparison with data from other sites and deep-sea cores suggests that, on balance, the most likely period represented by the sequence of samples is isotope stage 5, substages d-a, which agrees with Hendey & Volman (1986) as well, basically, as Butzer (1978) and Klein (1976). The evidence indicates that, as at other sites (Avery, 1982u), there was an expected time lag between environmental change as recorded in the micromammalian data and the appearance of evidence for human adaptation to that change. More specifically, it is suggested that the Howieson’s Poort industry may represent a response to an increase in the variety of terrestrial game. Subsequent reduction in this variety could be expected to prompt a return to a way of life similar to that followed previously.

Acknowledgements This project was supported by a grant from the CSIR Foundation for Research Develop- ment and facilitated by diligent preparation of samples by Mr M. J. Hallett and Mrs C. W. Brown. Prof. H. J. Deacon kindly extended an invitation to join his excavation at Klasies River Mouth. Dr R. G. Klein and another reviewer made helpful comments.

D. M. AVERY

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