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The micromammalian fauna from Border Cave, Kwazulu, South Africa
Journal
of Archaeological
Science 1982, 9, 187-204
The Micromammalian Fauna from Border Cave, Kwazulu, South Africa D. M. AveryThe micromammalian fauna from Border Cave is analysed in terms of community composition and structure. Changes in these aspects are interpreted as indicative of changes in vegetation and climate in the vicinity of the cave during the period of deposition. It would appear that vegetation comprised relatively extensive forest or thick bush and dense grass during wetter phases and fairly open savanna woodland, even open grassland, during drier periods. Variation through time in mean mandibular size in two speciesof Crocidura (musk shrew) was different both in the two species and from what was expected. It now seems likely that the size change constitutes a response to complex phenomena and not simply to changes in temperature. Comparison with the Boomplaas A sequence indicates that the same general pattern of change is reflected at both sites but that there was a greater amplitude of change at Boomplaas A and that IsO stage 4 was dry at this site but wet at Border Cave. Evidence for periodic changes in the distribution of various species,and in some casesthe mutually exclusive occurrence of ecologically equivalent species, has implications for the zoogeography of the species involved. In particular, the occurrence of Pelomys fallax (creek rat) in the lower half of the sequence is of interest in view of its present distribution 6Ot+ km north of Border Cave. BORDER CAVE, CLIMATE, MICROMAMMALS, VEGETATION, ZOOGEOGRAPHY.
Keywords:
SOUTH AFRICA
Introduction Border Cave is located at 27” 1’S, 31” 59’E, some 400 m from the border of Kwazulu with Swaziland (Figure 1). It is situated just below the escarpment of the Lebombo Mountains at an altitude of about 500 m, facing west over the lowveld. Details of the geomorphological setting are given in Butzer et al. (1978u), who further note that the climate of the area belongs to the summer-hot, mesothermal winter-dry Cwa type of Koeppen, with the lowveld being warm-thermal, semi-arid and the crest of the Lebombos being subhumid. The annual rainfall varies from 500 mm in the lowlands to 900 mm in the highlands and the indications are that Border Cave is presently frost-free. The vegetation of the area is subtropical, deciduous savanna and bush, now severely affected by overgrazing, cutting and burning. On the rocky hillsides and smaller valleys dense bush and thickets occur, whereas bush savanna and open acacia savanna are found on the Lebombo Mountains. More details are given in Butzer et al. (1978~) and Anderson (1978, p. 195) and photographs are provided by Beaumont (1978). “South African Museum, Cape Town, South Africa. 187 0305-4403/82/020187+18 $03.00/O 01982 AcademicPressInc. (London) Limited
188
D. M. AVERY c I 21
2!
0
I
2
3
4
5xiOOkm
Figure 1. Location of Border Cave and Boomplaas A together with the present-day most southerly record of Pelomys faIlax (F’f).
The site was first excavated by R. A. Dart in 1934 (unpublished); the most recent and detailed work has been that by Beaumont (1973, 1978). In Beaumont’s excavation 3A Rear a series of 11 sedimentary units was recognized which was thought to represent oxygen isotope stages 5d upwards, in total a period of about 115,000 years. (Units 12 to 15, representing perhaps a further 80,000 years, were present only in excavation 3B and contained no micromammalian remains.) For unit la a series of ‘*C dates was obtained ranging from 90f 105 bp (Pta-1728) in spit 1 to 590f70 bp (LJ-2890) in spit 3. The cultural material indicates that the site was occupied by Iron Age people during a period when conditions were essentially modern according to the sedimentological evidence (Butzer et al., 1978a, p. 329). During the period of deposition of unit lb the site was apparently unoccupied by people. Two dates, 13,300&150 bp (Pta-721) for spit 1 and 28,500f 1800 bp (LJ- ?) for spit 2, and sedimentological evidence for a cold and possibly dry climate suggest that this was during the upper pleniglacial IsO stage 2. (Butzer et al. (1978a, p. 325) note that a date of 2010&50 bp (Pta-506) for spit 1 may be based on contaminated material.) Unit 2 has a date of 33,OOOf2OOXlbp (LJ-2892) at the top and 38,600& 1500 bp (Pta-704) at the base; unit 3 also produced four very similar dates (see Table 4) and one of 45,000~2750/2200 (Pta-1190) which may have been based on contaminated material (Beaumont et al., 1978, p. 412). For both units the climate is described as mainly cold and possibly wet (Butzer et al., 1978a, p. 329), and the archaeological remains have been assigned to the early Later Stone Age. All the lower units, which are beyond the effective range of radiocarbon dating and have dates of greater than 40,000 years, contain Middle Stone Age material. Apart from the period of deposition of unit 4, and possibly units 7a/6, conditions were apparently generally cold according to the sedimentological data. Material, Methods and Rationale
The micromammalian material examined in the present study was recovered from excavation 3A Rear during the period 1970-75 (Beaumont, 1978). Initial remarks were made by de Graaff (1978) who concluded that conditions had at no time been substantially different from those pertaining today. In the present study only mandibles and
MICROMAMMALIAN
FAUNA
FROM
SOUTH
AFRICA
189
maxillae were identified and counted. Two methods were used for calculating minimum numbers of individuals when more than one stratigraphic unit or sub-unit was being treated as a whole. In both cases the left and right mandibles and maxillae were first counted separately. When there was some doubt as to the discreteness of the individual sub-units, for instance, in units la and lb, the scores for the different jaws from all the sub-units were added and the highest score was taken as the minimum number of individuals. Thus, a species is represented by one skeletal element in the grouped subunits in the same way that it would be in an individual unit. The total scores for units la and lb also include specimens whose exact provenance within the unit was not recorded and which could not therefore be assigned to particular sub-units. When dealing with sub-units which are possibly not discrete the aim has been to avoid counting the same individual twice since it is potentially feasible for different jaws of one animal to have been recovered from different spits or sub-units. If, however, the units that are to be grouped may be considered to be discrete no such precautions need be taken. It is therefore permissible to take the highest number for each unit regardless of skeletal element; in other words, left mandibles could be added to right maxillae without fear of raising the numbers artificially. This method of counting was used in cases where units were grouped for purposes of comparison with other work. In all cases the raw scores have been transformed into percentages (Table 1) in order to facilitate direct comparison between samples. There were some problems of identification that it was not possible to resolve at this stage. With Myosorex (forest shrew) and Tatera {gerbil) it was not possible to determine the species involved on the available material. In the first case either or both M. cafer and M. varius may be represented. As far as environmental reconstruction is concerned, however, it probably makes little or no difference since both species occupy similar habitats. On the other hand, whether T. brantsii or T. leucogaster is represented could affect the interpretation or at least allow greater precision. T. brantsii occurs principally in savanna grasslands whereas T. leucogaster is found mainly in savanna woodlands (Davis, 1974). Knowledge of the species involved could therefore provide some information on the extent to which grass was open or closed. It would appear that the most numerous Otomys (vlei rat) is 0. irroratus but it is possible that it might be 0. angoniensis. Both, however, live in very similar habitats so that again this will not materially affect the interpretation. Crocidura cf cyanea (reddish-grey musk shrew) may perhaps be C. silacea, from which it is in any case doubtfully distinguished, or C. mariquensis. The species is, however, very poorly represented and for this reason is of little importance. The species in the samples provide information concerning the type and disposition of the vegetation within the vicinity of the cave. This is because the distribution of small mammals tends to be governed mainly by vegetation type and secondly by abiotic factors such as the nature of the ground surface (Rosenzweig & Winakur, 1969; Bond et al., 1980). The extent of the area to which the evidence refers depends directly upon the size of the hunting range of the barn owls (Tyto alba) which are thought to have been responsible for accumulating the remains. Although the range varies according to the availability of prey, the approximate area probably lies within a 5 to 10 km radius of the cave. Topographic similarity over a larger area may, however, allow reasonable extrapolation of the data beyond the range of the owl. Moreover, a series of samples from stratified deposits allows identification of any changes in vegetation that may have occurred during the period of time represented by the samples. Some indication of the relative nature of the climate is afforded by analysis of the structure of the micromammalian community. This is based on the fact that communities that exist under harsh or unpredictable conditions tend to comprise fewer species of which one or a few will be dominant and the remainder barely represented.
Sub-total
indet.
N. thebaica R. cf clivosas M. tricolor E. cf hottehtotus E. capensis S. nigrita
2-78
---
4.17
-
-
2.56
1.39
2.56 -
16.67
15.37
Sub-total
Chiroptera
5.56 6.94
2.56 5.13
2 15-30
1.39 1.39 1.39 -
-
1 G15
2.56 2.56 2.56
Insectivora
Spit (ems)
A. hottentotus E. myurus Myosorex sp. S. infinitesimus C. bicolor C. cf cyanea C. Jlavescens C. hirta
Depth
la
-
-
-
-
15.87
794 4.76
3.17 -
3 30-46
2.08
co4 0.65
;5 _ -
_ -
0.52 0.52
-
13.64
1.47
_ 0.49
_ 0.49 0.49
7.84
0.98 441 0.98
0.49 0.49 _
0.65 0.65 _ 0.65 9.09 2.60
0.49 _
2 53-69
_
1 38-53
13.54
0.52 469 4.69
0.52 1.04 1.04 0.52 0.52
*Total
lb
-
-
-
7.14
7.14 -
-
-
3 69-84
0.28
-
-
1.12
-
0.28
-
8.78
-
_ _
_ _
20.62
_ 15.46 206
2.06
-
_ 702 0.88
0.88
1.03 -
3
-
-
0.28
0.28 0.28
_
9.26
0.56 6.18 140
_
0.56
0.28 -
*Total
2
-
-
-_ _ -
11.11
_ 9.52 -
-
1.59 -
4
-
-
_ -
_ -
IO.00
_ 10.00 -
-
-
Sa
-
-
_ -
_ -
7.32
4.88 -
244
-
5b
-
_
_ _
17.86
-
-
_ -
17.39
13.04 -
-
4.35 -
6
_ -
14.29 3.57
-
-
5c
Table I. Percentage representation of micromammalian species in individual units at Border Cave
-
-
_ _
_ _
10.52
I 5.26 -
F&j
-
la
-
-
-
10.52
_ _ 5.26 5.26
-
_
_ _
11.76
_ 5.88 5.88
-
8
_
_ _ _
_ _ _
13.34
_ 6.61 6.67 -
-
9
G3
10
1 3.48
llb
2.33
233 _ _ _
_ _ _
9.31
1 2.33 4.65
-
_ _ _
_ _ _
25.21
;74 6.95 13.04
1- x_ 1- __ _
-
lb
Rodentia
Iaminatus
N=
Sub-total
0. irroratus G. murinas
0.
P. palliatus C. hottentotus A. chrysophilus A. namaquensis D. incomtus L. griselda M. minutoides P. faNax P. natalensis R. pumilio T. dolichurus M. albicaudatus Tatera sp. D. cf melanotis D. cf mesomelas M. typica S. campestris S. pratensis
39
63
include
72
*Totals
84.14
1.39 1.39 2.78 4.17 20.83 2.78
2.56 769 28.21 -
79.19
12.70 1.59 6.35 6.35 1.59 3.17 6.35 4.76 28.57 1.59
16.67 1.39 1.39 2.78 2.78 1.39
8204
1.59
1.39
2.56 7.69 12.82 --2.56 _-10.26 2.56 5.13 -
-
1.59 7.94
-
2.78 4.17 11.11
-
0.65 3.90 6.49 27.27 -
154
85.72 14
9285
7.14 42-86 _
-
7.14 21.43 -
7.14 7.14 -
not assignable
204
90.70
0.49 0.49 5.88 19-61 -
Go
ii4 0.65 0.65 19.48 11.69 -
0.49 1.96 3.92 0.49 1.47 -4.90 0.98 0.98 38.73 9.31 0.98
0.65 1.95 1.95 0.65
specimens
192
8438
0.52 0.52 2.60 4.69 3.13 21.88 1.56
21.88 1.04 l-04 7.81 4.17 0.52
1.56 3.13 7-29 1.04 -
to individual
356
89.60
o-56 0.56 1.97 5.06 25.28 _
0.84 1.69 3.09 0.28 0.84 5.90 0.84 0.56 31.74 9.83 0.56
spits.
114
91.22
G5 1.75 2.63 29.82 1.75 0.88 789 28.07 -
0.88 9.65 4.39 0.88 0.88
97
79.37
&I6 2.06 l-03 30.93 6.19 1.03 10.31 16.49 -
1.03 2.06 5.15 1.03 -
63
88.90
z76 1.59 6.35 20.63 -
G4 11.11 _ _ 6.35 1.59 1.59 20.63 6.36
20
90.00
25.00 -
5.00 10.00 15.00 5.00 5.00 15.00 10.00
41
92.71
4.88 244 36.59 -
9.76 244 9.76 2.44 12.20 4.88 244 244 244
28
82.14
_ 10.71 25.00 -
14.29 10.71 3.57 14.29 3.57
23
82.62
-
-
4.35 8.70 13.04
19
89.48
47.37 -
-
5.26 10.53
5.26
-
-
38
89.45
2.63 34.21 -
2.63
15.79 7.89 5.26 2.63 2.63 7.89 2.63 2.63 2.63 -
17
88.21
29.41 -
-
11.76 5.88 5.88 5.88 11.76 5.88 5.88 5.88 -
15
86.68
43
88.40
465 2.33 4419
-
6.67 6.67 46.67
13.95 6.98 2.33 6-67 -
2.33
-
2.33 2.33 6.98
115
74.79
6.09 10.43 25.22
-
1.74 18.26 1.74 0.87
0.87
-
1.74 7.83
192
D. M. AVERY
A greater number of more evenly represented species characterises the community existing under optimum conditions (Krebs, 1978: 458). An index of general diversity such as the Shannon index H = - X(Pi log Pi) has proved useful for archaeological samples (Avery, 1982). (The base of the logarithms is immaterial but in the present calculations natural logarithms, log,, were used). Indices of constituent elements such as evenness, dominance and diversity may be used in conjunction with the general index but are less useful when taken independently, if only because they tend to be more affected by the size of the sample. Even with the Shannon index there may be problems connected with variation in sample size and in particular with small samples, as has been pointed out by T. P. Volman (pers. comm.). It is considered, however, that although this may affect the detailed quantitative results it does not invalidate the evidence for general trends and relative assessments of conditions which are discussed below. It is clear for instance both &at samples with similar numbers of individuals and of species may yet produce different H values, which must be significant, and also that lumping of samples does not effectively alter the basic pattern. Certain species, particularly the shrews Myosorex varius and Crocidura flavescens, have been shown to vary in size at different times in the past. This was attributed to the operation on a temporal scale of the so-called Bergmann’s Rule which states that within a given species those representatives living in colder climates will tend towards greater body mass. The present evidence, discussed below, suggests however that there is some doubt as to whether this is in fact the case. Apart from its uses in palaeoenvironmental reconstruction the fossil material constitutes an important source of information concerning the zoogeography of the species involved. This is particularly the case when the distribution of the species is different now from what it was in the past. Vegetational Reconstruction
It seems likely that the majority of the micromammalian species represented in the deposits occurred on the Lebombo Mountains, both the plateau and the dip slope, although a few will have occupied the slopes around the cave and perhaps even the plain below. This is because such an area would probably be most accessible to the owls occupying the cave, which is just below the top of the escarpment but about 450 m above the lowveld, and it is to be expected that the birds would prey upon the nearest good supply of food. Any vegetational interpretation will therefore apply primarily to the area above the cave. The most frequently occurring species (Table 1) may be divided into three main groups according to variation in their proportional representation (Figure 2). The largest group consists of species that occurred in greater proportions in units 9 or 10 up to 5a. The indication is that during this period the vegetation was relatively thick with dense grass, perhaps fairly damp (Otomys irroratus, Rhabdomys pumilio, Lemniscomys griselda), and rather more extensive forest or thick scrub (Thamnomys dolichurus). On the rocky slopes around the cave, bush and scrub will have occurred (Aethomys spp.). A. chrysophilus occurs in savanna woodland which would tend to confirm the more closed nature of the vegetation. A second group comprises species that occur more frequently in units 4 up to lb. This group suggests that open grassland was the dominant vegetation both on the plain (Mystromys albicaudatus, Otomys laminatus) and on the slopes (Crocidura Jlavescens). Tatera sp. belongs in this group, which is consistent with the general indication of grassland. In view of the fact that other species indicate open grassland it may be that Tatera brantsii is the species represented but this is by no means certain.
MICROMAMMALIAN
FAUNA
FROM
SOUTH
%
AFRICA
193
A. chrysophilus
A. namoquensis 1
L. arise/da
R. pumifio
% C. hirto
7: dolichurus
'01
P. nota&lls~s 20
0ilAAM.b
IO Toter0
50
0 h
0. irrorofm
40
S. campestris 30 ‘lh ‘“,1b
20
0. lominatus S. protemh
IO
abcdtfghijklmnop
‘IiL4n-a obcdtfghi
jklmnop
0u abcdtfghtlklmnop
Figure 2. Patterns of occurrence of selected species at Border Cave. (a = la, b = lb(l), c = lb(2), d = 2, e = 3, f = 4, g = Sa, h = 5b, i = 5c, j = 6, k = 7a, 1 = 7b, m = 8, n = 9, o = 10, p = llb.)
The third group includes species that exhibit a basic tendency towards being most numerous in the lowermost (1 lb) and uppermost (la) units. The general impression would seem to be of fairly open savanna woodland (Saccostomus campestris, Steatomys pratensis) but with some denser wetter vegetation (Praomys natalensis, Crocidura hirtu) perhaps closer to water. P. natalensis may have further significance because it has been shown to be a pioneer species which is at a clear advantage in changing or disturbed vegetation (Meester et al., 1979). It is also a semi-commensal species and it may be that its especially high incidence in unit la provides evidence of the beginnings of the effect of herding and agriculture on the vegetation. If changes are indicated in unit llb these presumably result from fairly major climatic changes.
194
D. M. AVERY
In his study of the macrofauna Klein (1977) suggests that at the time units 8/7 and 3/2 were being deposited the vegetation was bushier than at other times (Table 4). If the micromammalian data are grouped in comparable fashion the proportions of Thamnomys dolichurus would appear to confirm this suggestion with regard to units 8/7 when an increase in forest is indicated. A. chrysophilus suggests an increase in bush at the time of units S/7 but A. namaquensis indicates higher proportions at the time of units 6/4. This may mean that during the latter period the bush was more restricted to the hillsides and perhaps more spread over the flatter ground in the earlier period. Klein (1977) is, of course, referring basically to the flatter ground since his key animals tend to be the larger herding ungulates. The evidence of Aethomys spp. may not therefore be directly comparable since change in vegetation on slopes and flats might conceivably not coincide. The small mammal data which are comparable suggest that there was, in fact, a considerable amount of grass at all times but that its nature changed periodically, a point also made by Klein (1977, p. 18). In particular the very high proportions of M. albicaudatus in units 4 up to 1b suggest extensive open grasslands. At the time of unit 2 there was perhaps a minor increase in bush or forest but in general the evidence does not agree with Klein’s (1977) suggestion that at the time of units 3/2 the vegetation was relatively bushy. On the evidence of S. campestris and, to a certain extent, S. pratensis it would appear that there was open savanna woodland during the earliest period (units 11b to 9 = MSA 1) and the latest period (unit la = Iron Age). The implication for the earliest period agrees with the interpretation of Butzer et a/. (1978a) that the vegetation was temperate savanna woodland and could agree with Klein’s (1977) interpretation of open vegetation since the interpretations are, in any case, relative. In fact none of the interpretations may be contradictory since the data may refer to different situations. It is quite possible, for instance, that the amount of grassland available was adequate for the large herbivores represented, even at times when the vegetation might seem relatively bushy from the small mammal evidence. It is equally possible that the large and small mammal evidence may refer to either or both the lowveld and the Lebombos. Klein (1977) has assumed that his data refer to the lowveld but this might not be entirely the case. Many of the species presently occur in both the lowveld and the mountains whilst Redunca fulvorufula (mountain reedbuck) is found only in the Lebombos (Reilly, 1978). Moreover, Beaumont (1978) provides evidence from the raw material used by the occupants of the cave to indicate that these people were familiar with the mountain region and did not confine their attention to the lowveld, As far as the micromammals are concerned it has already been suggested above that the Lebombos are principally represented. Clearly, with an altitudinal discrepancy of some 450 m the provenance of the data could have considerable bearing on the interpretation of those data. If the provenance is constant the variation recorded would be relatively correct but if people or owls were to hunt different areas at different times this could certainly make the problem more complex. General Climatic Conditions
The Shannon index of general diversity (Table 2) indicates that conditions were different during the time the uppermost unit, la, was accumulated from those occurring at any other previous time represented in the sequence. This is contrary to the suggestion by de Graaff (1978), mentioned above, that no substantial change occurred. The relatively high diversity suggests that conditions were mildest during the latest period. This in turn suggests that l*O stage 5e is not represented in the samples since this stage is generally accepted as being the most recent occasion when conditions were as warm as they are today (Kukla, 1977). Such an interpretation would agree with the general opinion of
MICROMAMMALIAN Table 2. Variation Border Cave Level
N*
:“,
188 153 (1)
lb 2 3 4 Sa 5b 5c 6 la 7b 8 9 10 llb
(2)
312 5c/b la/6 8/7b 64 8/7 5 1019
201 114 97 63 20 41 28 23 19 38 17 15 42 115 211 69 42 2:: 79 123 57
FAUNA
FROM
SOUTH
in indices of micromammalian S+
AFRICA
195
community structure at
B
e
d
25 19 21 16 16 13 9 14 9 9 8 14 11 8 13 14
2.52 2.23 2.05 2.03 2.14 2.25 208 2.16 2.02 1.87 1.68 2.19 2.19 1.71 1.93 220
0.78 0.76 0.67 0.73 0.77 0.88 0.95 0.82 0.92 0.85 0.81 0.83 0.82 0.75 0.83
4.58 3.58 3.77 3.17 3.28 290 2.67 3.50 240 2.55 2.38 3.57 3.53 2.58 3.21 2.74
0.12 0.15 0.21 019 0.17 0.13 0.24 0.18 0.15 0.21 0.27 0.17 0.14 0.26 0.24 0.14
17 15 12 15 17 16 16 15
2.13 2.25 1.91 2.28 2.27 2.18 2.23
0.75 0.83 0.77 0.84 0.80 o-79 0.80 0.73
2.99 3.31 2.94 3.49 2.98 3.43 3.12 346
0.17 0.15 0.23 0.15 0.14 0.18 0.15 0.24
199
o-91
N = number of individuals. S = number of species. E = index of general diversity = - B(P, log, Pi) where of the sample in the ith species. e = index of evenness = g/log,S. d = index of diversity = S-1llog.N. c = index of dominance = Z(PZ,/N)~ = EP,B. *Chiroptera have been excluded from the calculations.
C
P, is the proportion
Butzer et al. (1978a) that stages 5d to 1 are represented in excavation 3A Rear. Apart from this the general indication is that conditions were relatively mild at the time of deposition of units 11b, 8/7b and 1b (1). Rather harsher conditions apparently pertained during the intervening periods when units 10/9,7a/6,3/2 and lb (2) were being deposited. The l*C dates for the upper half of the sequence allow a certain amount of correlation with the 180 stages. Unit la with dates around 500 bp is securely placed in stage 1 the Holocene, and this agrees with the suggested mild climate for this period. Unit lb(l) has a date of 13,300& 150 bp which would indicate that it represents the boundary between stages 1 and 2, that is, probably the Late Glacial period; the diversity index is intermediate between those for the preceding and succeeding periods. A date of 28,500&1800 bp in unit lb(2) would indicate that the beginning of the upper pleniglacial stage 2 is represented and the diversity index is fairly low. A sample representing the height of the last glacial maximum about 18,000 bp cannot be isolated; but this event is bracketed by the two dates for unit lb so that it is likely that the total level lb sample includes glacial maximum material. Conditions appear to have been deteriorating for some time previously, from the time when unit 2 was deposited (33,OOOf2000; 38,600&1500 bp); the unit 3 sample, with dates around 35,000 bp (see Table 4), and the combined units 3/2 sample indicate intermediate conditions. It is most likely that these can be interpreted as
196
D. M. AVERY
representing the transition between stages 3 and 2 or the final part of stage 3. A hiatus of perhaps 10,000 years may separate unit 3 from the underlying unit 4 which has a fairly high general diversity index. This should indicate relatively mild conditions probably equivalent to la0 stage 3c of Beaumont et al. (1978) while units 5ob may be equivalent to stage 3e. Units 7a/6 appear to equate with stage 4, units 8/7b with stage 5a, units 10/9 with stage 5b and unit 11b with stage 5c. Although it may be that the size of the samples is affecting the details of the interpretation it is important to note that at least in unit 6 downwards the units group in the same pairs as those suggested by Butzer et al. (1978a) and that the interpretation can be fitted to the generalized temperature curve given by Beaumont et al. (1978). This would argue in favour of the general validity of the method without suggesting that there are no problems attached to the use of small samples. Moreover, lumped samples still give the same picture as was pointed out above, and this should further encourage the view that the overall pattern is correct. It is to be noticed that the present proposed correlation of units with ‘*O stages suggests that the base of the sequence in unit 1lb represents stage 5c which is one stage later than was suggested by Butzer et al. (1978a) and Beaumont et al. (1978). However, these various authors do not agree on their internal interpretation of the sequence and it is Table 3. Variation inparameters measured in mandibles of Crocidura flavescens and C. hirta A: height of ascending ramus N Range R s C. flavescens la 6 lb(l) 12 lb(2) 12 2 14 3 15 5 21 7 7 llb 8
95 %*
B: depth of mandible at Milt N Range R s
95y
732-8.35 7.01-7.73 7.06-763 7.11-794 701-8.15 670-7.84 7.1 l-7.53 6.29-6.80
7.82 746 7.38 7.55 7.53 728 7.13 6.56
0.36 0.22 0.19 0.27 0.31 0.34 0.24 0.20
0.52 0.19 0.17 0.22 0.25 0.23 0.30 0.23
9 17 16 15 25 24 9 12
2.69-3.30 2.07-2.89 248-2.89 2.17-3.20 2.48-3.20 2.38-2.99 2.28-2.89 2.17-2.48
2.90 2.62 2.67 2.76 2.75 2.70 2.59 2.32
0.19 0.22 0.11 0.28 0.19 0.17 0.21 0.13
0.20 0.16 0.08 0.22 0.12 0.11 0.22 0.12
5.36-6.08 5.46623 5.98-6.60
5.75 5.92 6.18
0.18 0.32 0.27
0.16 0.55 0.24
15 6 21
1.86-2.38 2.07-2.58 1.86-2.59
2.14 2.26 2.16
0.14 0.19 0.16
0.11 0.27 0.11
C. hirta
C: length MI -a N Rm3e
8
D: lower tooth row N Range ;P
E : mandible+ incisor N Range 1
C. jiavescens 1 (1190) 2 11.50-11.75
(6.08) 5.67-5.87 5.77-5.98 (5.87)
5.80 5.84
556-5.77
5.62
2 11*10-11~20 1 (11.50) -
C. hirta la 7 4.33-4.95 lb 4 453-4.85 llb 2 4.85-4.95
4.61 4.72
7 8.25-9.70 3 8.87-9.18 -
:“, (1) lb (2) 2 3 ::
31 7 1 3
llb
1
1 (18.50) (1700) : 16.90-1780 2 17.30 2 1650-1720 2 16.95-1760 1 (1750)
9.05 9.01
*95% = confidence limits for the mean.
10 13.25-14.45 4 13.25-1405 1 (15.10)
17.23
13.86 13.58
MICROMAMMALIAN
FAUNA
FROM
SOUTH
AFRICA
197
clear that this is open to discussion. There is, for example, some doubt as to where or whether there are hiatuses in the sequence, and this must affect the interpretation. It is also likely that the physical response of rocks and the adaptation of small mammals to climatic change take place at different rates. Moreover, if Beaumont (1978) is correct in suggesting that the cave was occupied more or less mutually exclusively by humans and owls this could further influence the interpretation. Mandibles of CrociduraJIavescens and C. hirta were measured in various parameters (Table 3). Unfortunately there were too few specimens for reliable analysis and many of those present were broken. In spite of this limitation the results show that there is variation in the mean size of individual in different populations. Moreover it would appear that the direction of change is different in the two species. This has apparently led to a situation in unit 11b populations where there is partial overlap in the size range of the two species which has caused some problems of identification. Of particular interest is the fact that C. fiavescens at Border Cave is larger in the Holocene and smaller under glacial conditions. This is quite the reverse of its behaviour at Boomplaas A in the southern Cape (Avery, 1982). It would seem therefore that change in size cannot simply be correlated with temperature variation. Indeed, Scholander (1955) has argued convincingly that Bergmann’s Rule does not explain the climatic adaptation of homeotherms. More specifically, J. Meester @ers. comm.) has noted that although there is geographical variation in the size of C.#avescens in modem populations (Meester, 1963) this does not appear to be correlated with differences of temperature. An alternative correlation has been suggested by Tchemov (1968, p. 39) who recorded coincidental increase in annual rainfall and body size in one species of Bathyergidae in Israel. It has been suggested that Cryptomys hottentotus in South Africa may be exhibiting a similar response (Avery, 1982). If this is the case then an alternative explanation must be sought for changes in the Soricidae since the pattern of changes is different in the two families. When it is known more precisely which factors regulate distribution of C. flavescens as well as their relative importance it may be possible to decide what constitute optimal conditions for this species. Comparison of the mean size of individuals in populations existing under such conditions with those which occur at the limits of the range may then provide some insight into which factor is correlated with size. This will also presumably depend on whether or not it is advantageous or possible for individuals to increase in size under certain circumstances.
Comparison of the Border Cave and Boomplaas A Sequences
It is of some interest to compare the evidence of the micromammalian sequences from Border Cave and Boomplaas A. Both sites are situated in areas of high relief and provide long sequences covering essentially the same period of time. However, because Boomplaas A is much further south (Figure 1) it is to be expected that there will be differences. As far as the vegetation is concerned changes in the dominant life form and general physiognomy can be compared. At Boomplaas A the range is between scrub and restioid/ grassy vegetation on the hillsides and more or less dense grass on the valley floor. At Border Cave the variation is between relatively thick grass and forest or scrub and open grassland or woodland savanna. In both cases the indication is that during the Holocene and the interpleniglacial, l*O stages 1 and 3, the vegetation was relatively thicker and more closed. By contrast, during the upper pleniglacial the vegetation in both places was much more open, being predominantly grass at Border Cave and restioid/grassy at Boomplaas A.
198
D. M. AVERY
In terms of climate it would seem that at Boomplaas A the upper pleniglacial was colder than the lower pleniglacial but that both were relatively dry. At Border Cave, on the other hand, the evidence suggests that conditions were considerably wetter in the lower half of the sequence than they were in the upper half (unit 4 upwards). The general discrepancy between the southern Cape and the interior of South Africa, as well as the fact that the early and late glacial climate anomalies were different, has been documented by Butzer et al. (19786). These authors also refer to the effect of the Agulhas current on the climate of the country and the evident relationship between aridity and failure of the current. The fact that the current was apparently considerably weakened during the upper pleniglacial (prell & Hutson, 1979; Hutson, 1980), but perhaps not so weakened during the lower pleniglacial, could have caused the difference between pleniglacials at Border Cave. In the warmer intervals of the sequence precipitation was apparently relatively less effective, probably due to the higher evaporation rates that might be expected. If Mystromys albicaudatus is taken as representative of drier conditions and Otomys irroratus of wetter conditions this overall pattern can be seen in Figure 2. From this it would seem that IsO stage 2 was cool and dry whereas stages 4 and 5b were wet and cool at Border Cave. The dry lower pleniglacial at Boomplaas A must presumably be attributed to other causes, whether different circulation patterns or a different rainfall regime. Comparison of the general diversity indices at the two sites shows a consistent pattern. The Holocene is separated in both cases although, as might be expected, the difference between Holocene and Last Glacial is less at Border Cave than it is at Boomplaas A. There is a general coincidence of trends at both sites which appears too good to be fortuitous. It is tempting to interpret the higher indices at Border Cave as indicative of continuously milder conditions nearer the tropics than in the more southerly temperate surrounds of Boomplaas A. It may be, however, that these indices are an artifact of small sample size and although it is likely that relatively milder conditions did obtain at Border Cave, greater certainty must await larger samples. As far as archaeology is concerned it is of some interest to note an approximate coincidence at both sites of change from a middle stone age industry to a later stone age industry with the onset of the upper pleniglacial. The changeover appears to have occurred around 30,000 bp at Boomplaas A, rather after the beginning of the upper pleniglacial is recorded in the micromammalian evidence (Avery, 1982); at Border Cave the industrial change had apparently occurred by about 35,000 bp and coincided more with the transitional phase between the middle and upper pleniglacials. This interpretation is complicated by an apparent hiatus in the deposits of about 10,000 years immediately prior to 35,000 bp. Also, of course, it is difficult if not impossible to interpret the patterns of change in either environmental conditions or industrial advance with sufficient precision to allow definite correlations to be made. Beyond this one would not in any case necessarily expect strict contemporaneity at such widely separated sites; both the mechanisms of cultural change and the likelihood of different weather regimes would tend to militate against this. It does, however, provide some further support for the suggestion (Avery, 1982) that, at least until the Later Stone Age, there is likely to have been quite good correlation between gross environmental change and cultural development.
Zoogeography The majority of species that occurred regularly at Border Cave in the past is still to be found in the area today. There are, however, others that either no longer occur in the vicinity or apparently arrived in the region at a relatively late date. The complementary occurrence of pairs of species is also of some interest (Figure 2).
MICROMAMMALIAN
FAUNA
FROM
SOUTH
AFRICA
199
Of those species that have not been recovered from the lower units Dendromus cf mesomelas and Graphiurus murinus occurred only in the Holocene. Both species have a preference for trees but the presence of Thamnomys dolichurus in most units indicates that these were not lacking in the Pleistocene. It is unlikely to have been low temperatures that inhibited them, at least in the case of D. mesomelas since this species inhabits the alpine and subalpine zones in East Africa (Kingdon, 1974, p. 532). It may be that these species migrated to higher ground when the climate became drier and the lowveld became less suitable. That it was fairly dry at the time of unit lb(l) and la(2) is suggested by the presence of Malacothrix typica. This species is presently found in the South West Arid and Southern Savanna grassland zones, with the nearest recorded locality being some 200 km to the west of Border Cave (Davis, 1974, p. 169). It seems likely that a temporary extension of the range of this species was facilitated by the previous expansion of open grass during the upper pleniglacial. It is not clear why Dendromus cf melanotis should not have been present before about 20,000 bp in unit lb(2). It could be that it merely became relatively more numerous at that time because, being able to live at high montane altitudes (de Graaff, 198 l), it was perhaps at an advantage under cold conditions. This, however, does not explain why the species is also present in the Holocene and it may be that relative dryness is the common denominator. Otomys laminatus has not been recorded from the Lebombos but this gap may be more apparent than real; the distribution of this species has yet to be fully recorded and it is said to inhabit submontane and coastal grasslands (Davis, 1962, p. 63). It is, however, of some interest to note that 0. laminatus does not occur in the lowest four units at Border Cave, is most numerous in what are apparently the coldest units and less numerous again in the Holocene units. Indeed, it is not found at all in the uppermost spit and it may be that, in fact, this species does not occur in the Border Cave area in the warmest periods such as the warmer parts of the Last and Present Interglacials. It is possible that at such times bush and scrub encroach to such an extent that this species is driven out of the area or simply that the vegetation is too dry, as suggested by the presence of M. typica mentioned above. Otomys irroratus is also not recorded from the area and this is one reason for suggesting that the species represented may be 0. angoniensis. This species does occur in the Lebombos and is also a Southern Savanna woodland species whereas both 0. laminatus and 0. irroratus are Southern Savanna grassland species. It might perhaps be expected that the smaller species would behave in a similar fashion to 0. laminatus if it were 0. irroratus. In fact, however, it occurs throughout the sequence in appreciable numbers although there is a tendency towards a reduction in the upper units. Mystromys albicaudatus is another Southern Savanna grassland species which today is not recorded within about 200 km of Border Cave (Davis, 1974, p. 162). It does not occur in the lowest units of the sequence and is present only in much reduced numbers in the uppermost unit. It was most clearly able to advance in great numbers into what is presently Southern Savanna woodland at times in the past when the climate was colder and/or drier than it is today. During interglacial maxima, however, increased woodand and bush will have forced it to retreat once again. There is good correlation between this species and 0. laminatus and it seems likely that both are recording the same phenomena. Of particular interest is the fact that Pelomys fallax has been recovered from the lower half of the sequence. This species is presently found north of about 21”s (Davis, 1974, p. 153) and the nearest locality is some 600 km to the north of Border Cave (Figure 1). It seems likely that this species was obliged by falling temperatures to retreat nearer the Equator. That the habitat was not destroyed is indicated by the presence of Dasymys incomtus at Border Cave during what was apparently the coldest period (units 3 up to lb). This essentially complementary occurrence of the two species suggests that, although they may be found together today, D. incomtus probably has a greater tolerance of cold
Early LSA
open grassland on flats and slopes
moderate
COO1
-
2
1
‘*O stages
----___------3 12 transition
mild (Late Glacial) cool, dry
fairly open savanna very mild, dry woodland; some ranker vegetation
Iron Age
(sterile)
Vegetation
interpretation General climatic conditions
Industry
Micromammalian
---
45 f OOOt~~~
------
(Pta-1190)+*
36,800&- 1000 (Pta-422) 37,500-11200 (Pta-446) 36,100f900 (Pta-423) 35,700*1100 (Pta-424)
33,000~2000 (LJ-2892) 38,600* 1500 (Pta-704)
440435 (Ra-715) 500-170 w-2889) 590570 (W-2890) -__--_-----650f70 (W-2891) ______2010&50 (Pta-506)** 13,300*150 (Pta-721) 28,500&1800 (LJ-?)
90f105 @a-1728) 170f45 (Ra-870) XX&t45 (Pta-703)
W dates bp*
-
(mid) (b=)
3 (top)
@a=)
2 @OP)
8;
lb (spit 1)
la/b
(3)
(2)
la (spit 1)
Units
-
_ -
-
3/2 transition
2
1
-
cold, ?wet
cold, ?dry
modem
Butzer et al. (1978a) Climate I*0 stages
bushier, colder
Klein (1977)
Table 4. i%e environment of Border Cave, based on the micromammalian evidence, correlated with the interpretations of Butzer et al. (1978a) and Klein (1977)
Early MSA
EpiPietersburg/ Howieson’s Pool-t
Late MSA
5c
samples.
-____-___~5b
*From Butzer et al. (1978~). **Possibly based on contaminated
fairly open dry mild, dry savanna woodland; some ranker vegetation
--cool, wet
(Pta-719)
to ~48,500 (Pta-488)
42,000~~~
lib
9 10
8
7b -
---7a
6
_____
Sa -____5b
4
-
4
SC
> 48,700 (Pta-489)
> 42,300 (Pta-872) to >49,100 (Pta-1275)
413 transition
3
mild, relatively dry 5a
thick dense grass, moderate probably fairly damp; more exten- -sive forest or thick bush ; scrub on cool slopes
~--__-
mild, dry
---
-
-
-
warm
5d early
5d middle
5d late
5b
5a
cold to temperate
cold to temperate cold, wet
cold, wet
warm or dry
- - - 4/3 transition temperate - - - 4 cold, ?wet
3
-
more open, grassier
bushier, colder
more open, grassier, approximately as in historic period
202
D. M. AVERY
conditions. Neither species was recovered from the top unit which may indicate that the marshy habitat was destroyed. Possibly the dry conditions of the upper pleniglacial continued into the Holocene (as was suggested by M. typica) so that, in spite of suitable temperatures, P. fallax was yet unable to migrate south again. Another possibility is that the eventual introduction of farming or herding made it impossible for this species to move from one suitable habitat to another. Either or both of these agents could also have caused the relict distribution pattern noted by Davis (1974, p. 152) for D. incomtus. Lemniscomys griselda is a Southern Savanna woodland species and is absent from units 7a up to lb during a period when it was postulated above that the vegetation was much more open and grassy. L. griselda must therefore have been obliged to withdraw from the area during the Last Glacial; it shows, in effect, a negative correlation with M. afbicaudutus. Rhabdomys pumilio is present throughout the sequence although it is not recorded from the area today. Davis (1962, p. 62, but see 1974, p. 150) records it as replaced by L. griseldu in the eastern Transvaal lowveld and Zululand (KwaZulu) but it is perhaps possible that R. pumilio would occur on the Lebombos even if not at lower altitudes. In general terms Southern Savanna woodland species gradually declined in relation to grassland species until they reached their lowest point in unit lb(2). This is approaching the time of the upper pleniglacial when, it is postulated above, the vegetation was a good deal more open than it is at present. Thereafter there is at first a slight increase in the proportion of woodland species and then, in the uppermost unit, a significant increase. It would appear therefore that migration was cyclical on a long-term basis, and brought about by quite large changes in the vegetational structure. In this context it is to be noted that the grassland species disappeared completely during the warmest periods of the Last Interglacial whereas the same is apparently not true of the woodland species during the upper pleniglacial. This presumably was caused by the fact that during the interglacial times bush and forest might be expected to spread over the entire area whereas during glacial maxima there would remain refugia in the valleys even though the flatter ground supported open grass.
Conclusion
Analysis of the micromammalian fauna from Border Cave indicates that there was considerable change in the vegetation of the area. Generally speaking, however, the range of variation was not sufficiently great as to cause major changes in the composition of the fauna. Table 4 provides a summary of the changes in vegetation interpreted from the micromammalian fauna. In the lowest unit fairly dry open savanna woodland was probably dominant, but with a certain amount of rank vegetation, presumably along the rivers. Thereafter there appears to have been an extension of this vegetation and of forest or thick scrub. This can perhaps be attributed to an increase in effective precipitation which, in turn, could be due to declining temperatures rather than to increased rainfall. From unit 4 upwards the climate apparently became drier again as well as cooler and, particularly in units 3 up to lb, open grassland became the dominant vegetation. With the return of warmer conditions in unit la open savanna woodland was once again able to become established in the area. Thus it would seem that a full glacial/interglacial cycle is represented at Border Cave. Variations in the size of Crocidura jfavescens and C. hirta, instead of confirming previous findings at Boomplaas A and other southern Cape sites, have shown that factors relating to mean size in different populations are more complex than they appeared to be at first. It seems, in fact, that more than one environmental parameter is involved and it will require considerable work before it is possible to isolate these.
MICROMAMMALIAN
FAUNA FROM SOUTH AFRICA
203
Comparison of the Border Cave and Boomplaas A micromammalian sequences suggests that the same general pattern is discernible at both sites. There was, however, greater range of variation at Boomplaas A and some indication that the lower pleniglacial was dry at this site but wet at Border Cave. Although there were no major changes in the composition of the micromammalian fauna during the period under discussion there were differences. Some species were not present throughout and, in some cases, this could be correlated with the existence of glacial or interglacial conditions. Pelomys fallax, for instance, was apparently forced to retreat north during the Last Glacial and has never returned. It is also clear that of the Southern Savanna species grassland forms predominated during the glacial period whereas woodland forms became dominant under interglacial conditions. In general the micromammalian evidence agrees fairly well with that from the lithostratigraphy (Butzer et al., 1978a) and the macromammals (Klein, 1977). Where there are differences these may prove not to be insurmountable; they may, in fact, be due to the fact that different evidence relates to different aspects of the whole. Moreover, none of the various lines of evidence is ever complete and the size and nature of the omissions must inevitably influence the final interpretation.
Acknowledgement Mr P. B. Beaumont is thanked for providing access to the material upon which this report is based. Dr T. P. Volman offered useful constructive criticism.
References Anderson, J. (1978). Appendix 1. A survey of the extant flora in the vicinity of Border Cave. In (P. B. Beaumont) Border Cave. Unpubl. MA thesis, University of Cane Town. Avery, D. M. (1982). Micromammals as palaeoenvironmental indicators and an interpretation of the late Quaternary in the southern Cape Province, South Africa. Annals of the South African Museum 85, 183-374. Beaumont, P. B. (1973). Border Cave-a progress report. South African Journal of Science 69, 41-46. Beaumont, P. B. (1978). Border Cave. Unpubl. MA thesis, University of Cape Town. Beaumont, P. B., de Villiers, H. & Vogel, J. C. (1978). Modern man in sub-Saharan Africa prior to 49,000 years bp. : a review and evaluation with particular reference.to Border Cave. South African Journal of Science 74, 4099419. Bond, W., Ferguson, M. & Forsyth, G. (1980). Small mammals and habitat structure along altitudinal gradients in the southern Cape mountains. South African Journal of Zoology 15, 34-43. Butzer, K. W., Beaumont, P. B. & Vogel, J. C. (1978a). Lithostratigraphy of Border Cave, KwaZulu, South Africa; a Middle Stone Age sequence beginning c. 195,000 years bp. Journal of Archaeological Science 5, 317-341. Butzer, K. W., Stuckenrath, R., Bruzewicz, A. J. & Helgren, D. M. (1978b). Late Cenozoic paleoclimates of the Gaap Escarpment, Kalahari Margin, South Africa. Quaternary Research 10, 310-339. Davis, D. H. S. (1962). Distribution patterns of southern African Muridae, with notes on some of their fossil antecedants. Annals of the Cape Provincial Museums 2, 56-76. Davis, D. H. S. (1974). The distribution of some small southern African mammals (Mammalia: Insectivora, Rodentia). Annals of the Transvaal Museum 29, 135-184. Graaff, G. de (1978). Appendix 36. The microfaunal remains from Border Cave. In (P. B. Beaumont) Border Cave. Unpubl. MA thesis, University of Cape Town. Graaff, G. de (1981). The Rodents of South Africa. Durban: Butterworth. Hutson, W. H. (1980). The Agulhas Current during the Late Pleistocene: analysis of modern fauna1 analogs. Science 207, 6466.
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Kingdon, J. (1974). fist African mammals. IIB. Hares and rodents. London & New York: Academic Press. Klein, R. G. (1977). The mammalian fauna from the Middle and Later Stone Age (Later Pleistocene) levels at Border Cave, Natal Province, South Africa. South African Archaeological Bulletin 32, 14-27. Krebs, C. J. (1978). Ecology, 2nd Edn. New York: Harper & Row. Kukla, G. J. (1977). Pleistocene land - sea correlations. 1 Europe. Earth - Science Review 13, 307-374. Meester, J. (1963). A systematic revision of the shrew genus Crocidura in southern Africa. Transvaal Museum Memoirs
13.
Meester, J. A. J., Lloyd, C. N. V. & Rowe-Rowe, D. T. (1979). A note on the ecological role of Praomys natalensis. South African Journal of Science 75, 183-184. Prell, W. L. & Hutson, W. H. (1979). Zonal temperature-anomaly maps of Indian Ocean surface waters: modern and ice - age patterns. Science 206, 45U56. Reilly, T. E. (1978). Appendix 2. Some remarks relating to the larger mammals in the Hlane Game Sanctuary. In (P. B. Beaumont) Border Cave. Unpubl. MA thesis, University of Cape Town. Rosenzweig, M. L. & Winakur, J. (1969). Population ecology of desert communities: habitats and environmental complexity. Ecology 50, 558-572. Scholander, P. F. (1955). Evolution of climatic adaptation in homeotherms. Evolution 9, 15-26. Tchernov, E. (1968). Succession of rodent faunas during the Upper Pleistocene of Israel. Mammalia depicta. Hamburg: Paul Parey.
of Archaeological
Science 1982, 9, 187-204
The Micromammalian Fauna from Border Cave, Kwazulu, South Africa D. M. AveryThe micromammalian fauna from Border Cave is analysed in terms of community composition and structure. Changes in these aspects are interpreted as indicative of changes in vegetation and climate in the vicinity of the cave during the period of deposition. It would appear that vegetation comprised relatively extensive forest or thick bush and dense grass during wetter phases and fairly open savanna woodland, even open grassland, during drier periods. Variation through time in mean mandibular size in two speciesof Crocidura (musk shrew) was different both in the two species and from what was expected. It now seems likely that the size change constitutes a response to complex phenomena and not simply to changes in temperature. Comparison with the Boomplaas A sequence indicates that the same general pattern of change is reflected at both sites but that there was a greater amplitude of change at Boomplaas A and that IsO stage 4 was dry at this site but wet at Border Cave. Evidence for periodic changes in the distribution of various species,and in some casesthe mutually exclusive occurrence of ecologically equivalent species, has implications for the zoogeography of the species involved. In particular, the occurrence of Pelomys fallax (creek rat) in the lower half of the sequence is of interest in view of its present distribution 6Ot+ km north of Border Cave. BORDER CAVE, CLIMATE, MICROMAMMALS, VEGETATION, ZOOGEOGRAPHY.
Keywords:
SOUTH AFRICA
Introduction Border Cave is located at 27” 1’S, 31” 59’E, some 400 m from the border of Kwazulu with Swaziland (Figure 1). It is situated just below the escarpment of the Lebombo Mountains at an altitude of about 500 m, facing west over the lowveld. Details of the geomorphological setting are given in Butzer et al. (1978u), who further note that the climate of the area belongs to the summer-hot, mesothermal winter-dry Cwa type of Koeppen, with the lowveld being warm-thermal, semi-arid and the crest of the Lebombos being subhumid. The annual rainfall varies from 500 mm in the lowlands to 900 mm in the highlands and the indications are that Border Cave is presently frost-free. The vegetation of the area is subtropical, deciduous savanna and bush, now severely affected by overgrazing, cutting and burning. On the rocky hillsides and smaller valleys dense bush and thickets occur, whereas bush savanna and open acacia savanna are found on the Lebombo Mountains. More details are given in Butzer et al. (1978~) and Anderson (1978, p. 195) and photographs are provided by Beaumont (1978). “South African Museum, Cape Town, South Africa. 187 0305-4403/82/020187+18 $03.00/O 01982 AcademicPressInc. (London) Limited
188
D. M. AVERY c I 21
2!
0
I
2
3
4
5xiOOkm
Figure 1. Location of Border Cave and Boomplaas A together with the present-day most southerly record of Pelomys faIlax (F’f).
The site was first excavated by R. A. Dart in 1934 (unpublished); the most recent and detailed work has been that by Beaumont (1973, 1978). In Beaumont’s excavation 3A Rear a series of 11 sedimentary units was recognized which was thought to represent oxygen isotope stages 5d upwards, in total a period of about 115,000 years. (Units 12 to 15, representing perhaps a further 80,000 years, were present only in excavation 3B and contained no micromammalian remains.) For unit la a series of ‘*C dates was obtained ranging from 90f 105 bp (Pta-1728) in spit 1 to 590f70 bp (LJ-2890) in spit 3. The cultural material indicates that the site was occupied by Iron Age people during a period when conditions were essentially modern according to the sedimentological evidence (Butzer et al., 1978a, p. 329). During the period of deposition of unit lb the site was apparently unoccupied by people. Two dates, 13,300&150 bp (Pta-721) for spit 1 and 28,500f 1800 bp (LJ- ?) for spit 2, and sedimentological evidence for a cold and possibly dry climate suggest that this was during the upper pleniglacial IsO stage 2. (Butzer et al. (1978a, p. 325) note that a date of 2010&50 bp (Pta-506) for spit 1 may be based on contaminated material.) Unit 2 has a date of 33,OOOf2OOXlbp (LJ-2892) at the top and 38,600& 1500 bp (Pta-704) at the base; unit 3 also produced four very similar dates (see Table 4) and one of 45,000~2750/2200 (Pta-1190) which may have been based on contaminated material (Beaumont et al., 1978, p. 412). For both units the climate is described as mainly cold and possibly wet (Butzer et al., 1978a, p. 329), and the archaeological remains have been assigned to the early Later Stone Age. All the lower units, which are beyond the effective range of radiocarbon dating and have dates of greater than 40,000 years, contain Middle Stone Age material. Apart from the period of deposition of unit 4, and possibly units 7a/6, conditions were apparently generally cold according to the sedimentological data. Material, Methods and Rationale
The micromammalian material examined in the present study was recovered from excavation 3A Rear during the period 1970-75 (Beaumont, 1978). Initial remarks were made by de Graaff (1978) who concluded that conditions had at no time been substantially different from those pertaining today. In the present study only mandibles and
MICROMAMMALIAN
FAUNA
FROM
SOUTH
AFRICA
189
maxillae were identified and counted. Two methods were used for calculating minimum numbers of individuals when more than one stratigraphic unit or sub-unit was being treated as a whole. In both cases the left and right mandibles and maxillae were first counted separately. When there was some doubt as to the discreteness of the individual sub-units, for instance, in units la and lb, the scores for the different jaws from all the sub-units were added and the highest score was taken as the minimum number of individuals. Thus, a species is represented by one skeletal element in the grouped subunits in the same way that it would be in an individual unit. The total scores for units la and lb also include specimens whose exact provenance within the unit was not recorded and which could not therefore be assigned to particular sub-units. When dealing with sub-units which are possibly not discrete the aim has been to avoid counting the same individual twice since it is potentially feasible for different jaws of one animal to have been recovered from different spits or sub-units. If, however, the units that are to be grouped may be considered to be discrete no such precautions need be taken. It is therefore permissible to take the highest number for each unit regardless of skeletal element; in other words, left mandibles could be added to right maxillae without fear of raising the numbers artificially. This method of counting was used in cases where units were grouped for purposes of comparison with other work. In all cases the raw scores have been transformed into percentages (Table 1) in order to facilitate direct comparison between samples. There were some problems of identification that it was not possible to resolve at this stage. With Myosorex (forest shrew) and Tatera {gerbil) it was not possible to determine the species involved on the available material. In the first case either or both M. cafer and M. varius may be represented. As far as environmental reconstruction is concerned, however, it probably makes little or no difference since both species occupy similar habitats. On the other hand, whether T. brantsii or T. leucogaster is represented could affect the interpretation or at least allow greater precision. T. brantsii occurs principally in savanna grasslands whereas T. leucogaster is found mainly in savanna woodlands (Davis, 1974). Knowledge of the species involved could therefore provide some information on the extent to which grass was open or closed. It would appear that the most numerous Otomys (vlei rat) is 0. irroratus but it is possible that it might be 0. angoniensis. Both, however, live in very similar habitats so that again this will not materially affect the interpretation. Crocidura cf cyanea (reddish-grey musk shrew) may perhaps be C. silacea, from which it is in any case doubtfully distinguished, or C. mariquensis. The species is, however, very poorly represented and for this reason is of little importance. The species in the samples provide information concerning the type and disposition of the vegetation within the vicinity of the cave. This is because the distribution of small mammals tends to be governed mainly by vegetation type and secondly by abiotic factors such as the nature of the ground surface (Rosenzweig & Winakur, 1969; Bond et al., 1980). The extent of the area to which the evidence refers depends directly upon the size of the hunting range of the barn owls (Tyto alba) which are thought to have been responsible for accumulating the remains. Although the range varies according to the availability of prey, the approximate area probably lies within a 5 to 10 km radius of the cave. Topographic similarity over a larger area may, however, allow reasonable extrapolation of the data beyond the range of the owl. Moreover, a series of samples from stratified deposits allows identification of any changes in vegetation that may have occurred during the period of time represented by the samples. Some indication of the relative nature of the climate is afforded by analysis of the structure of the micromammalian community. This is based on the fact that communities that exist under harsh or unpredictable conditions tend to comprise fewer species of which one or a few will be dominant and the remainder barely represented.
Sub-total
indet.
N. thebaica R. cf clivosas M. tricolor E. cf hottehtotus E. capensis S. nigrita
2-78
---
4.17
-
-
2.56
1.39
2.56 -
16.67
15.37
Sub-total
Chiroptera
5.56 6.94
2.56 5.13
2 15-30
1.39 1.39 1.39 -
-
1 G15
2.56 2.56 2.56
Insectivora
Spit (ems)
A. hottentotus E. myurus Myosorex sp. S. infinitesimus C. bicolor C. cf cyanea C. Jlavescens C. hirta
Depth
la
-
-
-
-
15.87
794 4.76
3.17 -
3 30-46
2.08
co4 0.65
;5 _ -
_ -
0.52 0.52
-
13.64
1.47
_ 0.49
_ 0.49 0.49
7.84
0.98 441 0.98
0.49 0.49 _
0.65 0.65 _ 0.65 9.09 2.60
0.49 _
2 53-69
_
1 38-53
13.54
0.52 469 4.69
0.52 1.04 1.04 0.52 0.52
*Total
lb
-
-
-
7.14
7.14 -
-
-
3 69-84
0.28
-
-
1.12
-
0.28
-
8.78
-
_ _
_ _
20.62
_ 15.46 206
2.06
-
_ 702 0.88
0.88
1.03 -
3
-
-
0.28
0.28 0.28
_
9.26
0.56 6.18 140
_
0.56
0.28 -
*Total
2
-
-
-_ _ -
11.11
_ 9.52 -
-
1.59 -
4
-
-
_ -
_ -
IO.00
_ 10.00 -
-
-
Sa
-
-
_ -
_ -
7.32
4.88 -
244
-
5b
-
_
_ _
17.86
-
-
_ -
17.39
13.04 -
-
4.35 -
6
_ -
14.29 3.57
-
-
5c
Table I. Percentage representation of micromammalian species in individual units at Border Cave
-
-
_ _
_ _
10.52
I 5.26 -
F&j
-
la
-
-
-
10.52
_ _ 5.26 5.26
-
_
_ _
11.76
_ 5.88 5.88
-
8
_
_ _ _
_ _ _
13.34
_ 6.61 6.67 -
-
9
G3
10
1 3.48
llb
2.33
233 _ _ _
_ _ _
9.31
1 2.33 4.65
-
_ _ _
_ _ _
25.21
;74 6.95 13.04
1- x_ 1- __ _
-
lb
Rodentia
Iaminatus
N=
Sub-total
0. irroratus G. murinas
0.
P. palliatus C. hottentotus A. chrysophilus A. namaquensis D. incomtus L. griselda M. minutoides P. faNax P. natalensis R. pumilio T. dolichurus M. albicaudatus Tatera sp. D. cf melanotis D. cf mesomelas M. typica S. campestris S. pratensis
39
63
include
72
*Totals
84.14
1.39 1.39 2.78 4.17 20.83 2.78
2.56 769 28.21 -
79.19
12.70 1.59 6.35 6.35 1.59 3.17 6.35 4.76 28.57 1.59
16.67 1.39 1.39 2.78 2.78 1.39
8204
1.59
1.39
2.56 7.69 12.82 --2.56 _-10.26 2.56 5.13 -
-
1.59 7.94
-
2.78 4.17 11.11
-
0.65 3.90 6.49 27.27 -
154
85.72 14
9285
7.14 42-86 _
-
7.14 21.43 -
7.14 7.14 -
not assignable
204
90.70
0.49 0.49 5.88 19-61 -
Go
ii4 0.65 0.65 19.48 11.69 -
0.49 1.96 3.92 0.49 1.47 -4.90 0.98 0.98 38.73 9.31 0.98
0.65 1.95 1.95 0.65
specimens
192
8438
0.52 0.52 2.60 4.69 3.13 21.88 1.56
21.88 1.04 l-04 7.81 4.17 0.52
1.56 3.13 7-29 1.04 -
to individual
356
89.60
o-56 0.56 1.97 5.06 25.28 _
0.84 1.69 3.09 0.28 0.84 5.90 0.84 0.56 31.74 9.83 0.56
spits.
114
91.22
G5 1.75 2.63 29.82 1.75 0.88 789 28.07 -
0.88 9.65 4.39 0.88 0.88
97
79.37
&I6 2.06 l-03 30.93 6.19 1.03 10.31 16.49 -
1.03 2.06 5.15 1.03 -
63
88.90
z76 1.59 6.35 20.63 -
G4 11.11 _ _ 6.35 1.59 1.59 20.63 6.36
20
90.00
25.00 -
5.00 10.00 15.00 5.00 5.00 15.00 10.00
41
92.71
4.88 244 36.59 -
9.76 244 9.76 2.44 12.20 4.88 244 244 244
28
82.14
_ 10.71 25.00 -
14.29 10.71 3.57 14.29 3.57
23
82.62
-
-
4.35 8.70 13.04
19
89.48
47.37 -
-
5.26 10.53
5.26
-
-
38
89.45
2.63 34.21 -
2.63
15.79 7.89 5.26 2.63 2.63 7.89 2.63 2.63 2.63 -
17
88.21
29.41 -
-
11.76 5.88 5.88 5.88 11.76 5.88 5.88 5.88 -
15
86.68
43
88.40
465 2.33 4419
-
6.67 6.67 46.67
13.95 6.98 2.33 6-67 -
2.33
-
2.33 2.33 6.98
115
74.79
6.09 10.43 25.22
-
1.74 18.26 1.74 0.87
0.87
-
1.74 7.83
192
D. M. AVERY
A greater number of more evenly represented species characterises the community existing under optimum conditions (Krebs, 1978: 458). An index of general diversity such as the Shannon index H = - X(Pi log Pi) has proved useful for archaeological samples (Avery, 1982). (The base of the logarithms is immaterial but in the present calculations natural logarithms, log,, were used). Indices of constituent elements such as evenness, dominance and diversity may be used in conjunction with the general index but are less useful when taken independently, if only because they tend to be more affected by the size of the sample. Even with the Shannon index there may be problems connected with variation in sample size and in particular with small samples, as has been pointed out by T. P. Volman (pers. comm.). It is considered, however, that although this may affect the detailed quantitative results it does not invalidate the evidence for general trends and relative assessments of conditions which are discussed below. It is clear for instance both &at samples with similar numbers of individuals and of species may yet produce different H values, which must be significant, and also that lumping of samples does not effectively alter the basic pattern. Certain species, particularly the shrews Myosorex varius and Crocidura flavescens, have been shown to vary in size at different times in the past. This was attributed to the operation on a temporal scale of the so-called Bergmann’s Rule which states that within a given species those representatives living in colder climates will tend towards greater body mass. The present evidence, discussed below, suggests however that there is some doubt as to whether this is in fact the case. Apart from its uses in palaeoenvironmental reconstruction the fossil material constitutes an important source of information concerning the zoogeography of the species involved. This is particularly the case when the distribution of the species is different now from what it was in the past. Vegetational Reconstruction
It seems likely that the majority of the micromammalian species represented in the deposits occurred on the Lebombo Mountains, both the plateau and the dip slope, although a few will have occupied the slopes around the cave and perhaps even the plain below. This is because such an area would probably be most accessible to the owls occupying the cave, which is just below the top of the escarpment but about 450 m above the lowveld, and it is to be expected that the birds would prey upon the nearest good supply of food. Any vegetational interpretation will therefore apply primarily to the area above the cave. The most frequently occurring species (Table 1) may be divided into three main groups according to variation in their proportional representation (Figure 2). The largest group consists of species that occurred in greater proportions in units 9 or 10 up to 5a. The indication is that during this period the vegetation was relatively thick with dense grass, perhaps fairly damp (Otomys irroratus, Rhabdomys pumilio, Lemniscomys griselda), and rather more extensive forest or thick scrub (Thamnomys dolichurus). On the rocky slopes around the cave, bush and scrub will have occurred (Aethomys spp.). A. chrysophilus occurs in savanna woodland which would tend to confirm the more closed nature of the vegetation. A second group comprises species that occur more frequently in units 4 up to lb. This group suggests that open grassland was the dominant vegetation both on the plain (Mystromys albicaudatus, Otomys laminatus) and on the slopes (Crocidura Jlavescens). Tatera sp. belongs in this group, which is consistent with the general indication of grassland. In view of the fact that other species indicate open grassland it may be that Tatera brantsii is the species represented but this is by no means certain.
MICROMAMMALIAN
FAUNA
FROM
SOUTH
%
AFRICA
193
A. chrysophilus
A. namoquensis 1
L. arise/da
R. pumifio
% C. hirto
7: dolichurus
'01
P. nota&lls~s 20
0ilAAM.b
IO Toter0
50
0 h
0. irrorofm
40
S. campestris 30 ‘lh ‘“,1b
20
0. lominatus S. protemh
IO
abcdtfghijklmnop
‘IiL4n-a obcdtfghi
jklmnop
0u abcdtfghtlklmnop
Figure 2. Patterns of occurrence of selected species at Border Cave. (a = la, b = lb(l), c = lb(2), d = 2, e = 3, f = 4, g = Sa, h = 5b, i = 5c, j = 6, k = 7a, 1 = 7b, m = 8, n = 9, o = 10, p = llb.)
The third group includes species that exhibit a basic tendency towards being most numerous in the lowermost (1 lb) and uppermost (la) units. The general impression would seem to be of fairly open savanna woodland (Saccostomus campestris, Steatomys pratensis) but with some denser wetter vegetation (Praomys natalensis, Crocidura hirtu) perhaps closer to water. P. natalensis may have further significance because it has been shown to be a pioneer species which is at a clear advantage in changing or disturbed vegetation (Meester et al., 1979). It is also a semi-commensal species and it may be that its especially high incidence in unit la provides evidence of the beginnings of the effect of herding and agriculture on the vegetation. If changes are indicated in unit llb these presumably result from fairly major climatic changes.
194
D. M. AVERY
In his study of the macrofauna Klein (1977) suggests that at the time units 8/7 and 3/2 were being deposited the vegetation was bushier than at other times (Table 4). If the micromammalian data are grouped in comparable fashion the proportions of Thamnomys dolichurus would appear to confirm this suggestion with regard to units 8/7 when an increase in forest is indicated. A. chrysophilus suggests an increase in bush at the time of units S/7 but A. namaquensis indicates higher proportions at the time of units 6/4. This may mean that during the latter period the bush was more restricted to the hillsides and perhaps more spread over the flatter ground in the earlier period. Klein (1977) is, of course, referring basically to the flatter ground since his key animals tend to be the larger herding ungulates. The evidence of Aethomys spp. may not therefore be directly comparable since change in vegetation on slopes and flats might conceivably not coincide. The small mammal data which are comparable suggest that there was, in fact, a considerable amount of grass at all times but that its nature changed periodically, a point also made by Klein (1977, p. 18). In particular the very high proportions of M. albicaudatus in units 4 up to 1b suggest extensive open grasslands. At the time of unit 2 there was perhaps a minor increase in bush or forest but in general the evidence does not agree with Klein’s (1977) suggestion that at the time of units 3/2 the vegetation was relatively bushy. On the evidence of S. campestris and, to a certain extent, S. pratensis it would appear that there was open savanna woodland during the earliest period (units 11b to 9 = MSA 1) and the latest period (unit la = Iron Age). The implication for the earliest period agrees with the interpretation of Butzer et a/. (1978a) that the vegetation was temperate savanna woodland and could agree with Klein’s (1977) interpretation of open vegetation since the interpretations are, in any case, relative. In fact none of the interpretations may be contradictory since the data may refer to different situations. It is quite possible, for instance, that the amount of grassland available was adequate for the large herbivores represented, even at times when the vegetation might seem relatively bushy from the small mammal evidence. It is equally possible that the large and small mammal evidence may refer to either or both the lowveld and the Lebombos. Klein (1977) has assumed that his data refer to the lowveld but this might not be entirely the case. Many of the species presently occur in both the lowveld and the mountains whilst Redunca fulvorufula (mountain reedbuck) is found only in the Lebombos (Reilly, 1978). Moreover, Beaumont (1978) provides evidence from the raw material used by the occupants of the cave to indicate that these people were familiar with the mountain region and did not confine their attention to the lowveld, As far as the micromammals are concerned it has already been suggested above that the Lebombos are principally represented. Clearly, with an altitudinal discrepancy of some 450 m the provenance of the data could have considerable bearing on the interpretation of those data. If the provenance is constant the variation recorded would be relatively correct but if people or owls were to hunt different areas at different times this could certainly make the problem more complex. General Climatic Conditions
The Shannon index of general diversity (Table 2) indicates that conditions were different during the time the uppermost unit, la, was accumulated from those occurring at any other previous time represented in the sequence. This is contrary to the suggestion by de Graaff (1978), mentioned above, that no substantial change occurred. The relatively high diversity suggests that conditions were mildest during the latest period. This in turn suggests that l*O stage 5e is not represented in the samples since this stage is generally accepted as being the most recent occasion when conditions were as warm as they are today (Kukla, 1977). Such an interpretation would agree with the general opinion of
MICROMAMMALIAN Table 2. Variation Border Cave Level
N*
:“,
188 153 (1)
lb 2 3 4 Sa 5b 5c 6 la 7b 8 9 10 llb
(2)
312 5c/b la/6 8/7b 64 8/7 5 1019
201 114 97 63 20 41 28 23 19 38 17 15 42 115 211 69 42 2:: 79 123 57
FAUNA
FROM
SOUTH
in indices of micromammalian S+
AFRICA
195
community structure at
B
e
d
25 19 21 16 16 13 9 14 9 9 8 14 11 8 13 14
2.52 2.23 2.05 2.03 2.14 2.25 208 2.16 2.02 1.87 1.68 2.19 2.19 1.71 1.93 220
0.78 0.76 0.67 0.73 0.77 0.88 0.95 0.82 0.92 0.85 0.81 0.83 0.82 0.75 0.83
4.58 3.58 3.77 3.17 3.28 290 2.67 3.50 240 2.55 2.38 3.57 3.53 2.58 3.21 2.74
0.12 0.15 0.21 019 0.17 0.13 0.24 0.18 0.15 0.21 0.27 0.17 0.14 0.26 0.24 0.14
17 15 12 15 17 16 16 15
2.13 2.25 1.91 2.28 2.27 2.18 2.23
0.75 0.83 0.77 0.84 0.80 o-79 0.80 0.73
2.99 3.31 2.94 3.49 2.98 3.43 3.12 346
0.17 0.15 0.23 0.15 0.14 0.18 0.15 0.24
199
o-91
N = number of individuals. S = number of species. E = index of general diversity = - B(P, log, Pi) where of the sample in the ith species. e = index of evenness = g/log,S. d = index of diversity = S-1llog.N. c = index of dominance = Z(PZ,/N)~ = EP,B. *Chiroptera have been excluded from the calculations.
C
P, is the proportion
Butzer et al. (1978a) that stages 5d to 1 are represented in excavation 3A Rear. Apart from this the general indication is that conditions were relatively mild at the time of deposition of units 11b, 8/7b and 1b (1). Rather harsher conditions apparently pertained during the intervening periods when units 10/9,7a/6,3/2 and lb (2) were being deposited. The l*C dates for the upper half of the sequence allow a certain amount of correlation with the 180 stages. Unit la with dates around 500 bp is securely placed in stage 1 the Holocene, and this agrees with the suggested mild climate for this period. Unit lb(l) has a date of 13,300& 150 bp which would indicate that it represents the boundary between stages 1 and 2, that is, probably the Late Glacial period; the diversity index is intermediate between those for the preceding and succeeding periods. A date of 28,500&1800 bp in unit lb(2) would indicate that the beginning of the upper pleniglacial stage 2 is represented and the diversity index is fairly low. A sample representing the height of the last glacial maximum about 18,000 bp cannot be isolated; but this event is bracketed by the two dates for unit lb so that it is likely that the total level lb sample includes glacial maximum material. Conditions appear to have been deteriorating for some time previously, from the time when unit 2 was deposited (33,OOOf2000; 38,600&1500 bp); the unit 3 sample, with dates around 35,000 bp (see Table 4), and the combined units 3/2 sample indicate intermediate conditions. It is most likely that these can be interpreted as
196
D. M. AVERY
representing the transition between stages 3 and 2 or the final part of stage 3. A hiatus of perhaps 10,000 years may separate unit 3 from the underlying unit 4 which has a fairly high general diversity index. This should indicate relatively mild conditions probably equivalent to la0 stage 3c of Beaumont et al. (1978) while units 5ob may be equivalent to stage 3e. Units 7a/6 appear to equate with stage 4, units 8/7b with stage 5a, units 10/9 with stage 5b and unit 11b with stage 5c. Although it may be that the size of the samples is affecting the details of the interpretation it is important to note that at least in unit 6 downwards the units group in the same pairs as those suggested by Butzer et al. (1978a) and that the interpretation can be fitted to the generalized temperature curve given by Beaumont et al. (1978). This would argue in favour of the general validity of the method without suggesting that there are no problems attached to the use of small samples. Moreover, lumped samples still give the same picture as was pointed out above, and this should further encourage the view that the overall pattern is correct. It is to be noticed that the present proposed correlation of units with ‘*O stages suggests that the base of the sequence in unit 1lb represents stage 5c which is one stage later than was suggested by Butzer et al. (1978a) and Beaumont et al. (1978). However, these various authors do not agree on their internal interpretation of the sequence and it is Table 3. Variation inparameters measured in mandibles of Crocidura flavescens and C. hirta A: height of ascending ramus N Range R s C. flavescens la 6 lb(l) 12 lb(2) 12 2 14 3 15 5 21 7 7 llb 8
95 %*
B: depth of mandible at Milt N Range R s
95y
732-8.35 7.01-7.73 7.06-763 7.11-794 701-8.15 670-7.84 7.1 l-7.53 6.29-6.80
7.82 746 7.38 7.55 7.53 728 7.13 6.56
0.36 0.22 0.19 0.27 0.31 0.34 0.24 0.20
0.52 0.19 0.17 0.22 0.25 0.23 0.30 0.23
9 17 16 15 25 24 9 12
2.69-3.30 2.07-2.89 248-2.89 2.17-3.20 2.48-3.20 2.38-2.99 2.28-2.89 2.17-2.48
2.90 2.62 2.67 2.76 2.75 2.70 2.59 2.32
0.19 0.22 0.11 0.28 0.19 0.17 0.21 0.13
0.20 0.16 0.08 0.22 0.12 0.11 0.22 0.12
5.36-6.08 5.46623 5.98-6.60
5.75 5.92 6.18
0.18 0.32 0.27
0.16 0.55 0.24
15 6 21
1.86-2.38 2.07-2.58 1.86-2.59
2.14 2.26 2.16
0.14 0.19 0.16
0.11 0.27 0.11
C. hirta
C: length MI -a N Rm3e
8
D: lower tooth row N Range ;P
E : mandible+ incisor N Range 1
C. jiavescens 1 (1190) 2 11.50-11.75
(6.08) 5.67-5.87 5.77-5.98 (5.87)
5.80 5.84
556-5.77
5.62
2 11*10-11~20 1 (11.50) -
C. hirta la 7 4.33-4.95 lb 4 453-4.85 llb 2 4.85-4.95
4.61 4.72
7 8.25-9.70 3 8.87-9.18 -
:“, (1) lb (2) 2 3 ::
31 7 1 3
llb
1
1 (18.50) (1700) : 16.90-1780 2 17.30 2 1650-1720 2 16.95-1760 1 (1750)
9.05 9.01
*95% = confidence limits for the mean.
10 13.25-14.45 4 13.25-1405 1 (15.10)
17.23
13.86 13.58
MICROMAMMALIAN
FAUNA
FROM
SOUTH
AFRICA
197
clear that this is open to discussion. There is, for example, some doubt as to where or whether there are hiatuses in the sequence, and this must affect the interpretation. It is also likely that the physical response of rocks and the adaptation of small mammals to climatic change take place at different rates. Moreover, if Beaumont (1978) is correct in suggesting that the cave was occupied more or less mutually exclusively by humans and owls this could further influence the interpretation. Mandibles of CrociduraJIavescens and C. hirta were measured in various parameters (Table 3). Unfortunately there were too few specimens for reliable analysis and many of those present were broken. In spite of this limitation the results show that there is variation in the mean size of individual in different populations. Moreover it would appear that the direction of change is different in the two species. This has apparently led to a situation in unit 11b populations where there is partial overlap in the size range of the two species which has caused some problems of identification. Of particular interest is the fact that C. fiavescens at Border Cave is larger in the Holocene and smaller under glacial conditions. This is quite the reverse of its behaviour at Boomplaas A in the southern Cape (Avery, 1982). It would seem therefore that change in size cannot simply be correlated with temperature variation. Indeed, Scholander (1955) has argued convincingly that Bergmann’s Rule does not explain the climatic adaptation of homeotherms. More specifically, J. Meester @ers. comm.) has noted that although there is geographical variation in the size of C.#avescens in modem populations (Meester, 1963) this does not appear to be correlated with differences of temperature. An alternative correlation has been suggested by Tchemov (1968, p. 39) who recorded coincidental increase in annual rainfall and body size in one species of Bathyergidae in Israel. It has been suggested that Cryptomys hottentotus in South Africa may be exhibiting a similar response (Avery, 1982). If this is the case then an alternative explanation must be sought for changes in the Soricidae since the pattern of changes is different in the two families. When it is known more precisely which factors regulate distribution of C. flavescens as well as their relative importance it may be possible to decide what constitute optimal conditions for this species. Comparison of the mean size of individuals in populations existing under such conditions with those which occur at the limits of the range may then provide some insight into which factor is correlated with size. This will also presumably depend on whether or not it is advantageous or possible for individuals to increase in size under certain circumstances.
Comparison of the Border Cave and Boomplaas A Sequences
It is of some interest to compare the evidence of the micromammalian sequences from Border Cave and Boomplaas A. Both sites are situated in areas of high relief and provide long sequences covering essentially the same period of time. However, because Boomplaas A is much further south (Figure 1) it is to be expected that there will be differences. As far as the vegetation is concerned changes in the dominant life form and general physiognomy can be compared. At Boomplaas A the range is between scrub and restioid/ grassy vegetation on the hillsides and more or less dense grass on the valley floor. At Border Cave the variation is between relatively thick grass and forest or scrub and open grassland or woodland savanna. In both cases the indication is that during the Holocene and the interpleniglacial, l*O stages 1 and 3, the vegetation was relatively thicker and more closed. By contrast, during the upper pleniglacial the vegetation in both places was much more open, being predominantly grass at Border Cave and restioid/grassy at Boomplaas A.
198
D. M. AVERY
In terms of climate it would seem that at Boomplaas A the upper pleniglacial was colder than the lower pleniglacial but that both were relatively dry. At Border Cave, on the other hand, the evidence suggests that conditions were considerably wetter in the lower half of the sequence than they were in the upper half (unit 4 upwards). The general discrepancy between the southern Cape and the interior of South Africa, as well as the fact that the early and late glacial climate anomalies were different, has been documented by Butzer et al. (19786). These authors also refer to the effect of the Agulhas current on the climate of the country and the evident relationship between aridity and failure of the current. The fact that the current was apparently considerably weakened during the upper pleniglacial (prell & Hutson, 1979; Hutson, 1980), but perhaps not so weakened during the lower pleniglacial, could have caused the difference between pleniglacials at Border Cave. In the warmer intervals of the sequence precipitation was apparently relatively less effective, probably due to the higher evaporation rates that might be expected. If Mystromys albicaudatus is taken as representative of drier conditions and Otomys irroratus of wetter conditions this overall pattern can be seen in Figure 2. From this it would seem that IsO stage 2 was cool and dry whereas stages 4 and 5b were wet and cool at Border Cave. The dry lower pleniglacial at Boomplaas A must presumably be attributed to other causes, whether different circulation patterns or a different rainfall regime. Comparison of the general diversity indices at the two sites shows a consistent pattern. The Holocene is separated in both cases although, as might be expected, the difference between Holocene and Last Glacial is less at Border Cave than it is at Boomplaas A. There is a general coincidence of trends at both sites which appears too good to be fortuitous. It is tempting to interpret the higher indices at Border Cave as indicative of continuously milder conditions nearer the tropics than in the more southerly temperate surrounds of Boomplaas A. It may be, however, that these indices are an artifact of small sample size and although it is likely that relatively milder conditions did obtain at Border Cave, greater certainty must await larger samples. As far as archaeology is concerned it is of some interest to note an approximate coincidence at both sites of change from a middle stone age industry to a later stone age industry with the onset of the upper pleniglacial. The changeover appears to have occurred around 30,000 bp at Boomplaas A, rather after the beginning of the upper pleniglacial is recorded in the micromammalian evidence (Avery, 1982); at Border Cave the industrial change had apparently occurred by about 35,000 bp and coincided more with the transitional phase between the middle and upper pleniglacials. This interpretation is complicated by an apparent hiatus in the deposits of about 10,000 years immediately prior to 35,000 bp. Also, of course, it is difficult if not impossible to interpret the patterns of change in either environmental conditions or industrial advance with sufficient precision to allow definite correlations to be made. Beyond this one would not in any case necessarily expect strict contemporaneity at such widely separated sites; both the mechanisms of cultural change and the likelihood of different weather regimes would tend to militate against this. It does, however, provide some further support for the suggestion (Avery, 1982) that, at least until the Later Stone Age, there is likely to have been quite good correlation between gross environmental change and cultural development.
Zoogeography The majority of species that occurred regularly at Border Cave in the past is still to be found in the area today. There are, however, others that either no longer occur in the vicinity or apparently arrived in the region at a relatively late date. The complementary occurrence of pairs of species is also of some interest (Figure 2).
MICROMAMMALIAN
FAUNA
FROM
SOUTH
AFRICA
199
Of those species that have not been recovered from the lower units Dendromus cf mesomelas and Graphiurus murinus occurred only in the Holocene. Both species have a preference for trees but the presence of Thamnomys dolichurus in most units indicates that these were not lacking in the Pleistocene. It is unlikely to have been low temperatures that inhibited them, at least in the case of D. mesomelas since this species inhabits the alpine and subalpine zones in East Africa (Kingdon, 1974, p. 532). It may be that these species migrated to higher ground when the climate became drier and the lowveld became less suitable. That it was fairly dry at the time of unit lb(l) and la(2) is suggested by the presence of Malacothrix typica. This species is presently found in the South West Arid and Southern Savanna grassland zones, with the nearest recorded locality being some 200 km to the west of Border Cave (Davis, 1974, p. 169). It seems likely that a temporary extension of the range of this species was facilitated by the previous expansion of open grass during the upper pleniglacial. It is not clear why Dendromus cf melanotis should not have been present before about 20,000 bp in unit lb(2). It could be that it merely became relatively more numerous at that time because, being able to live at high montane altitudes (de Graaff, 198 l), it was perhaps at an advantage under cold conditions. This, however, does not explain why the species is also present in the Holocene and it may be that relative dryness is the common denominator. Otomys laminatus has not been recorded from the Lebombos but this gap may be more apparent than real; the distribution of this species has yet to be fully recorded and it is said to inhabit submontane and coastal grasslands (Davis, 1962, p. 63). It is, however, of some interest to note that 0. laminatus does not occur in the lowest four units at Border Cave, is most numerous in what are apparently the coldest units and less numerous again in the Holocene units. Indeed, it is not found at all in the uppermost spit and it may be that, in fact, this species does not occur in the Border Cave area in the warmest periods such as the warmer parts of the Last and Present Interglacials. It is possible that at such times bush and scrub encroach to such an extent that this species is driven out of the area or simply that the vegetation is too dry, as suggested by the presence of M. typica mentioned above. Otomys irroratus is also not recorded from the area and this is one reason for suggesting that the species represented may be 0. angoniensis. This species does occur in the Lebombos and is also a Southern Savanna woodland species whereas both 0. laminatus and 0. irroratus are Southern Savanna grassland species. It might perhaps be expected that the smaller species would behave in a similar fashion to 0. laminatus if it were 0. irroratus. In fact, however, it occurs throughout the sequence in appreciable numbers although there is a tendency towards a reduction in the upper units. Mystromys albicaudatus is another Southern Savanna grassland species which today is not recorded within about 200 km of Border Cave (Davis, 1974, p. 162). It does not occur in the lowest units of the sequence and is present only in much reduced numbers in the uppermost unit. It was most clearly able to advance in great numbers into what is presently Southern Savanna woodland at times in the past when the climate was colder and/or drier than it is today. During interglacial maxima, however, increased woodand and bush will have forced it to retreat once again. There is good correlation between this species and 0. laminatus and it seems likely that both are recording the same phenomena. Of particular interest is the fact that Pelomys fallax has been recovered from the lower half of the sequence. This species is presently found north of about 21”s (Davis, 1974, p. 153) and the nearest locality is some 600 km to the north of Border Cave (Figure 1). It seems likely that this species was obliged by falling temperatures to retreat nearer the Equator. That the habitat was not destroyed is indicated by the presence of Dasymys incomtus at Border Cave during what was apparently the coldest period (units 3 up to lb). This essentially complementary occurrence of the two species suggests that, although they may be found together today, D. incomtus probably has a greater tolerance of cold
Early LSA
open grassland on flats and slopes
moderate
COO1
-
2
1
‘*O stages
----___------3 12 transition
mild (Late Glacial) cool, dry
fairly open savanna very mild, dry woodland; some ranker vegetation
Iron Age
(sterile)
Vegetation
interpretation General climatic conditions
Industry
Micromammalian
---
45 f OOOt~~~
------
(Pta-1190)+*
36,800&- 1000 (Pta-422) 37,500-11200 (Pta-446) 36,100f900 (Pta-423) 35,700*1100 (Pta-424)
33,000~2000 (LJ-2892) 38,600* 1500 (Pta-704)
440435 (Ra-715) 500-170 w-2889) 590570 (W-2890) -__--_-----650f70 (W-2891) ______2010&50 (Pta-506)** 13,300*150 (Pta-721) 28,500&1800 (LJ-?)
90f105 @a-1728) 170f45 (Ra-870) XX&t45 (Pta-703)
W dates bp*
-
(mid) (b=)
3 (top)
@a=)
2 @OP)
8;
lb (spit 1)
la/b
(3)
(2)
la (spit 1)
Units
-
_ -
-
3/2 transition
2
1
-
cold, ?wet
cold, ?dry
modem
Butzer et al. (1978a) Climate I*0 stages
bushier, colder
Klein (1977)
Table 4. i%e environment of Border Cave, based on the micromammalian evidence, correlated with the interpretations of Butzer et al. (1978a) and Klein (1977)
Early MSA
EpiPietersburg/ Howieson’s Pool-t
Late MSA
5c
samples.
-____-___~5b
*From Butzer et al. (1978~). **Possibly based on contaminated
fairly open dry mild, dry savanna woodland; some ranker vegetation
--cool, wet
(Pta-719)
to ~48,500 (Pta-488)
42,000~~~
lib
9 10
8
7b -
---7a
6
_____
Sa -____5b
4
-
4
SC
> 48,700 (Pta-489)
> 42,300 (Pta-872) to >49,100 (Pta-1275)
413 transition
3
mild, relatively dry 5a
thick dense grass, moderate probably fairly damp; more exten- -sive forest or thick bush ; scrub on cool slopes
~--__-
mild, dry
---
-
-
-
warm
5d early
5d middle
5d late
5b
5a
cold to temperate
cold to temperate cold, wet
cold, wet
warm or dry
- - - 4/3 transition temperate - - - 4 cold, ?wet
3
-
more open, grassier
bushier, colder
more open, grassier, approximately as in historic period
202
D. M. AVERY
conditions. Neither species was recovered from the top unit which may indicate that the marshy habitat was destroyed. Possibly the dry conditions of the upper pleniglacial continued into the Holocene (as was suggested by M. typica) so that, in spite of suitable temperatures, P. fallax was yet unable to migrate south again. Another possibility is that the eventual introduction of farming or herding made it impossible for this species to move from one suitable habitat to another. Either or both of these agents could also have caused the relict distribution pattern noted by Davis (1974, p. 152) for D. incomtus. Lemniscomys griselda is a Southern Savanna woodland species and is absent from units 7a up to lb during a period when it was postulated above that the vegetation was much more open and grassy. L. griselda must therefore have been obliged to withdraw from the area during the Last Glacial; it shows, in effect, a negative correlation with M. afbicaudutus. Rhabdomys pumilio is present throughout the sequence although it is not recorded from the area today. Davis (1962, p. 62, but see 1974, p. 150) records it as replaced by L. griseldu in the eastern Transvaal lowveld and Zululand (KwaZulu) but it is perhaps possible that R. pumilio would occur on the Lebombos even if not at lower altitudes. In general terms Southern Savanna woodland species gradually declined in relation to grassland species until they reached their lowest point in unit lb(2). This is approaching the time of the upper pleniglacial when, it is postulated above, the vegetation was a good deal more open than it is at present. Thereafter there is at first a slight increase in the proportion of woodland species and then, in the uppermost unit, a significant increase. It would appear therefore that migration was cyclical on a long-term basis, and brought about by quite large changes in the vegetational structure. In this context it is to be noted that the grassland species disappeared completely during the warmest periods of the Last Interglacial whereas the same is apparently not true of the woodland species during the upper pleniglacial. This presumably was caused by the fact that during the interglacial times bush and forest might be expected to spread over the entire area whereas during glacial maxima there would remain refugia in the valleys even though the flatter ground supported open grass.
Conclusion
Analysis of the micromammalian fauna from Border Cave indicates that there was considerable change in the vegetation of the area. Generally speaking, however, the range of variation was not sufficiently great as to cause major changes in the composition of the fauna. Table 4 provides a summary of the changes in vegetation interpreted from the micromammalian fauna. In the lowest unit fairly dry open savanna woodland was probably dominant, but with a certain amount of rank vegetation, presumably along the rivers. Thereafter there appears to have been an extension of this vegetation and of forest or thick scrub. This can perhaps be attributed to an increase in effective precipitation which, in turn, could be due to declining temperatures rather than to increased rainfall. From unit 4 upwards the climate apparently became drier again as well as cooler and, particularly in units 3 up to lb, open grassland became the dominant vegetation. With the return of warmer conditions in unit la open savanna woodland was once again able to become established in the area. Thus it would seem that a full glacial/interglacial cycle is represented at Border Cave. Variations in the size of Crocidura jfavescens and C. hirta, instead of confirming previous findings at Boomplaas A and other southern Cape sites, have shown that factors relating to mean size in different populations are more complex than they appeared to be at first. It seems, in fact, that more than one environmental parameter is involved and it will require considerable work before it is possible to isolate these.
MICROMAMMALIAN
FAUNA FROM SOUTH AFRICA
203
Comparison of the Border Cave and Boomplaas A micromammalian sequences suggests that the same general pattern is discernible at both sites. There was, however, greater range of variation at Boomplaas A and some indication that the lower pleniglacial was dry at this site but wet at Border Cave. Although there were no major changes in the composition of the micromammalian fauna during the period under discussion there were differences. Some species were not present throughout and, in some cases, this could be correlated with the existence of glacial or interglacial conditions. Pelomys fallax, for instance, was apparently forced to retreat north during the Last Glacial and has never returned. It is also clear that of the Southern Savanna species grassland forms predominated during the glacial period whereas woodland forms became dominant under interglacial conditions. In general the micromammalian evidence agrees fairly well with that from the lithostratigraphy (Butzer et al., 1978a) and the macromammals (Klein, 1977). Where there are differences these may prove not to be insurmountable; they may, in fact, be due to the fact that different evidence relates to different aspects of the whole. Moreover, none of the various lines of evidence is ever complete and the size and nature of the omissions must inevitably influence the final interpretation.
Acknowledgement Mr P. B. Beaumont is thanked for providing access to the material upon which this report is based. Dr T. P. Volman offered useful constructive criticism.
References Anderson, J. (1978). Appendix 1. A survey of the extant flora in the vicinity of Border Cave. In (P. B. Beaumont) Border Cave. Unpubl. MA thesis, University of Cane Town. Avery, D. M. (1982). Micromammals as palaeoenvironmental indicators and an interpretation of the late Quaternary in the southern Cape Province, South Africa. Annals of the South African Museum 85, 183-374. Beaumont, P. B. (1973). Border Cave-a progress report. South African Journal of Science 69, 41-46. Beaumont, P. B. (1978). Border Cave. Unpubl. MA thesis, University of Cape Town. Beaumont, P. B., de Villiers, H. & Vogel, J. C. (1978). Modern man in sub-Saharan Africa prior to 49,000 years bp. : a review and evaluation with particular reference.to Border Cave. South African Journal of Science 74, 4099419. Bond, W., Ferguson, M. & Forsyth, G. (1980). Small mammals and habitat structure along altitudinal gradients in the southern Cape mountains. South African Journal of Zoology 15, 34-43. Butzer, K. W., Beaumont, P. B. & Vogel, J. C. (1978a). Lithostratigraphy of Border Cave, KwaZulu, South Africa; a Middle Stone Age sequence beginning c. 195,000 years bp. Journal of Archaeological Science 5, 317-341. Butzer, K. W., Stuckenrath, R., Bruzewicz, A. J. & Helgren, D. M. (1978b). Late Cenozoic paleoclimates of the Gaap Escarpment, Kalahari Margin, South Africa. Quaternary Research 10, 310-339. Davis, D. H. S. (1962). Distribution patterns of southern African Muridae, with notes on some of their fossil antecedants. Annals of the Cape Provincial Museums 2, 56-76. Davis, D. H. S. (1974). The distribution of some small southern African mammals (Mammalia: Insectivora, Rodentia). Annals of the Transvaal Museum 29, 135-184. Graaff, G. de (1978). Appendix 36. The microfaunal remains from Border Cave. In (P. B. Beaumont) Border Cave. Unpubl. MA thesis, University of Cape Town. Graaff, G. de (1981). The Rodents of South Africa. Durban: Butterworth. Hutson, W. H. (1980). The Agulhas Current during the Late Pleistocene: analysis of modern fauna1 analogs. Science 207, 6466.
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Kingdon, J. (1974). fist African mammals. IIB. Hares and rodents. London & New York: Academic Press. Klein, R. G. (1977). The mammalian fauna from the Middle and Later Stone Age (Later Pleistocene) levels at Border Cave, Natal Province, South Africa. South African Archaeological Bulletin 32, 14-27. Krebs, C. J. (1978). Ecology, 2nd Edn. New York: Harper & Row. Kukla, G. J. (1977). Pleistocene land - sea correlations. 1 Europe. Earth - Science Review 13, 307-374. Meester, J. (1963). A systematic revision of the shrew genus Crocidura in southern Africa. Transvaal Museum Memoirs
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Meester, J. A. J., Lloyd, C. N. V. & Rowe-Rowe, D. T. (1979). A note on the ecological role of Praomys natalensis. South African Journal of Science 75, 183-184. Prell, W. L. & Hutson, W. H. (1979). Zonal temperature-anomaly maps of Indian Ocean surface waters: modern and ice - age patterns. Science 206, 45U56. Reilly, T. E. (1978). Appendix 2. Some remarks relating to the larger mammals in the Hlane Game Sanctuary. In (P. B. Beaumont) Border Cave. Unpubl. MA thesis, University of Cape Town. Rosenzweig, M. L. & Winakur, J. (1969). Population ecology of desert communities: habitats and environmental complexity. Ecology 50, 558-572. Scholander, P. F. (1955). Evolution of climatic adaptation in homeotherms. Evolution 9, 15-26. Tchernov, E. (1968). Succession of rodent faunas during the Upper Pleistocene of Israel. Mammalia depicta. Hamburg: Paul Parey.