Palaeoecology of Miocene sites in Western Kenya

E. M. Nesbit Evans Vincent Wildlife Trust, Otter Haven Project, 84 Cornwall Gardens, London SW7 4AY, U.K.

Judith A. H. Van Couvering University of Colorado Museum, Boulder, Colorado 80302, U.S.A.

Peter Andrews British Museum (Natural History), Cromwell Road, London S W 7 5BD, U.K.

Received 7 July 1980 Keywords : Palaeoenvironments, indicator species, mammalian communities, ecological spectra.

Palaeoecology of Miocene Sites in Western Kenya The palaeoecology of the Miocene sites of Western Kenya is reviewed. Because fossil floras are usually not preserved the evidence on palaeoecology is mostly obtained from the fossil faunas. These are analysed by five methods : analysis of indicator species, habitat spectra, taxonomic habitat indices, ecological diversity analyses, and socio-ecology. The results indicate that the Songhor fauna was probably derived from forest habitat close to the place of deposition. In the Koru area the faunas from the Legetet Formation and the Chamtwara Member of the Kapurtay Agglomerates were similarly derived from forest habitats, but the Koru Formation fauna indicates more open conditions. The Rusinga and Karungu faunas have not been analysed in detail, and as they are associated with flood plain sedimentary environments it is probable that they are biased and not representative of any one living community, although there is some evidence also for forest conditions. This is supported by evidence from the fossil flora of Rusinga. Two Middle Miocene faunas from Maboko and Fort Ternan both indicate the presence of woodland or woodland savanna habitats, suggesting a major ecological shift from the faunal habitat of the Early Miocene.

1. I n t r o d u c t i o n

I n the E a r l y M i o c e n e the region o f C e n t r a l a n d Eastern K e n y a was a low d o m e of a n c i e n t P r e c a m b r i a n rocks, with isolated strato-volcanoes such as E l g o n a n d Kisingiri w i t h erosional r e m n a n t s o f earlier surfaces (e.g. the C h e r a n g a n i Hills), b r e a k i n g u p the o t h e r wise m o n o t o n o u s l a n d s c a p e (Bishop & T r e n d a l , 1966). This region was p r e d o m i n a n t l y covered b y rainforest, as the m o i s t u r e - l a d e n tropical c o n v e r g e n t w i n d currents blew u n i n t e r r u p t e d from the A t l a n t i c ( A n d r e w s & V a n Couvering, 1975). Some areas were p r o b a b l y unforested; sedimentological a n d p a l a e o b o t a n i c a l evidence suggests t h a t d u r i n g e r u p t i v e periods there were b a r r e n slopes a n d u n d r a i n e d regions w h i c h were h i g h l y a l k a l i n e a n d thus were either b a r r e n , or covered only w i t h a l k a l o p h i l i c plants ( H a m i l t o n , 1968; A n d r e w s & V a n Couvering, 1975). I n a d d i t i o n there w e r e p r o b a b l y forest glades, m u c h as there a r e t o d a y (cf. R i c h a r d s , 1952). C e r t a i n floras suggest t h a t w o o d l a n d s also existed, b u t these seem to have been m i n o r j u d g i n g from the m a j o r i t y of the p l a n t a n d a n i m a l evidence (Chaney, 1933; A x e l r o d & R a v e n , 1978). T h e E a r l y M i o c e n e forest c h r o n o f a u n a existed v i r t u a l l y u n c h a n g e d for six m i l l i o n years in this setting. F a u n a l R e s e m b l a n c e Indices (Simpson, 1949, 1960) show g r e a t similarities b e t w e e n the E a r l y M i o c e n e faunas ( V a n C o u v e r i n g & V a n Couvering, 1976; Pickford, this v o l u m e ) , b u t this l a n d s c a p e a n d the faunas c h a n g e d c h a r a c t e r d r a s t i c a l l y in M i d d l e M i o c e n e times. T h e central p a r t o f the K e n y a d o m e was uplifted a p p r o x i m a t e l y 300 m (Baker et al., 1972), faulting d i s r u p t e d portions o f the d o m e ; flood lavas e r u p t e d ; a n d the p a t t e r n o f i n t e r n a l d r a i n a g e in small fault-block basins b e g a n n o r t h o f T i n d e r e t in the Eastern Rift (Bishop & Pickford, 1975; M a r t y n , 1969). T h u s a t the t i m e t h a t the F o r t T e r n a n fossil beds were b e i n g d e p o s i t e d the l a n d s c a p e m u s t have consisted o f a l a v a

Journal of Human Evolution (1981) 10, 99-116

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9 1981 Academic Press Inc. (London) Limited

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E . M . NESBIT EVANS

plain stretching away to the south with local relief provided by Tinderet. Accompanying the marked change in geography was a marked change in the fauna and presumably the flora. The problems of assessing Miocene environments are those encountered in trying to interpret any palaeoenvironment. The data available for reconstructions are obtained from the sediments in which the fossils are found or with which they are associated, the fossilized flora and fauna itself, and the regionally reconstructed palaeogeography and palaeoclimate. I f the floras of fossil sites were commonly well represented, and the ecological significance of the component species was clearly understood, this would provide the best possible information on palaeoenvironments. However, in general, most of the plant parts which are taxonomically and ecologically most useful are subject to rapid decay and good fossil plant material is not often obtainable. An overall picture of the Miocene flora is to be found in Andrews & Van Couvering (1975), but these authors also look in more detail at Rusinga and Mfwangano. Although a few specimens of plant material have been found at all the East African Miocene sites, these two sites have the best variety of species and number of specimens. Andrews & V a n Couvering (1975) conclude that the original interpretation of a gallery forest (Chesters, 1957) was incorrect, and the environment at these two sites was extensive evergreen forest, which was lowland in part at least. Axelrod & Raven (1978), in their review of the African floral record disagree somewhat and suggest that there was more woodland present in the Early Miocene than has hitherto been thought. This argument cannot be resolved without further work on the Rusinga leaf flora and the discovery of new floras. The dearth of fossil plant material has led to a situation in which most palaeoenvironmental analyses are based on assessments of the fauna found at that site and interpretation of the sedimentary evidence. The use of a fauna for such purposes is open to criticism because it has been shown that the animals can be derived from several different habitats, and because they occur together as a "death assemblage", which has unknown relation to their association in life, selective fossilization of different species and different body parts can take place, thereby introducing bias to the fossil record (Behrensmeyer, 1975; Hill, 1979). We attempt to resolve this issue by restricting our interpretations to those sites which contain relatively undisturbed death assemblages and which therefore reflect the living assemblage accurately. Among the faunal assemblages, invertebrates have been found from all the East African Miocene sites. Land gastropods are particularly valuable for reconstructions of palaeoenvironments as the fossil faunas contain m a n y extant genera and m a n y of these are habitat specific (Verdcourt, 1963, 1972). Ecological studies are in progress currently to try to learn more about the habitat preferences of modern gastropods in these environments, but preliminary work based on Verdcourt's analysis (Andrews & V a n Couvering, 1975) summarized what is known at present of their habitat preferences and show that at most of the Miocene sites it is the forest-living snails which predominate. By far the most numerous faunal element in the Kenyan Miocene sites consists of mammals, although in m a n y sites turtles, crocodiles, lizards and snakes are found in large numbers, and birds also occur in small numbers. Most elements of these Miocene m a m m a l i a n faunas differ from their modern counterparts at various taxonomic levels, and in extrapolating their ecological affinities this has to be taken into account. An evolving lineage m a y take advantage of a new habitat, and there is the further possibility that the ecosystem itself m a y change over time. These problems are discussed below.

MIOGENE P A L A E O E C O L O G Y IN K E N Y A

10l

2. Methods o f Palaeoecological Analysis o f Faunas Several methods of evaluating palaeoenvironments based on the fauna have been used. These include: (1) indicator species, (2) habitat spectra, (3) taxonomic habitat indices, (4) ecological diversity spectra and indices, (5) socioecological categories. Where evidence is available from the flora this will, of course, be considered, but at most fossil localities the only evidence comes from the fauna.

Indicator Species Early approaches aimed at interpreting palaeoenvironments from their faunas relied for the most past on "indicator species". These species were either extant or closely related to living species, with a marked preference for one habitat type or had discrete functional specializations for particular habitats. T h e fossil animals were assumed to have had the same habitat preferences as their living counterparts, and it was inferred that the fauna was derived from this type of habitat. A major problem with this method is that few m a m m a l s are habitat specific to the necessary degree, and it is also possible that these specificities can change with time and space. T h e best examples of"indicator species" are those animals highly adapted to forest (Kingdon, 1971) or desert conditions. Another problem with this method is that reliance on single species or a few animals can be misleading unless it is absolutely certain that no faunal mixing has taken Place and the entire fauna is derived from the same habitat. Forest faunas contain numerous animals that are generally restricted to forest habitats. In African forests m a n y of the arboreal primates fall into this category, especially some of the apes, colobine monkeys and lorisine prosimians. Other arboreal mammals, such as the anomalurid flying "squirrels", m a n y of the true squirrels and m a n y small carnivores (e,g. genets) are also exclusively forest dwelling. Certain scansorial and terrestrial rodent species occupy the ground and ground vegetation of the forest floor, and several groups of entirely terrestrial m a m m a l s are also confined to forest, for example the tragulids, some suids, most cephalophines, the tenrecs and the rhynchocyonines. Among the nonm a m m a l i a n faunas the land gastropods provide the most distinctive forest indicators, especially the streptaxids, usually in association with Homorus. Certain lizards, snakes and birds are also restricted to forest, but have not yet been well studied. At the other extreme there are some animals which have become adapted to open semi-desert environments. Often they show some physiological or anatomical adaptation to body temperature regulation or heat avoidance as well as water independence such as in Camelus dromedarius or Oryx beisa and rodents. Animals with cursorial and hopping adaptations are common in this kind of habitat, as for example gazelles, alcelophines and hippotragines which run and gerbils and pedetids which hop. H a b i t a t types intermediate between these two extremes are varied and their faunas show some overlap. It is therefore difficult to distinguish variation between woodland, bushland and grassland on the basis of indicator species alone. The faunas are dominated by cursorial artiodactyls and carnivores, and the most characteristic mammals are the giraffids, reduncine and tragelaphine bovids, erinaceids, leporids and some cricetids. None of these are absolute indicators, but an abundance of these taxa would probably indicate some form of wooded bushland or grassland habitat. Where there is a preponderance of grazing animals, this is taken to indicate that a high proportion of the habitat is grassland, while predominance of animals with browsing adaptations is considered to indicate a higher proportion of woodland or bushland in the environment.

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NESBIT EVANS

Analysis of Faunas as Communities Analysis of the whole fauna, or in some cases, the m a m m a l i a n part of the fauna is more accurate than relying on just indicator species. We have been involved for the last few years in developing methods or using methods of community analysis used by ecologists to do this. I n addition, m a n y of these methods can be used for studying changes in habitats, biomes and community structure through time.

Habitat Spectra Habitat spectra were originally developed by Van Couvering, Solounias and Walker (Van Couvering, 1980) for predicting past habitats based on an analysis of the whole fauna rather than on key indicator species. The morphology of each species and its closeness of relationship with living species are considered in the analysis together with its range of possible habitats. This provides a weighting that is applied to each animal based on a scale from 0 to 6: extant species have a weighting of 6, extant genera of 5; subfamilies 4, and so on. These weightings are applied to a fossil fauna, each element of which is given a range of possible habitats, and the weighted species total is then calculated for each habitat type in turn. The pattern that emerges m a y then show dominance of one habitat type and this is taken to be the main habitat type of that fauna.

Taxonomic Habitat Indices Another approach to determining habitat by analysis of the whole m a m m a l i a n fauna was developed by Andrews and Nesbit Evans a n d is presented here for the first time. This method makes an assessment of the habitat preferences at various taxonomic levels for all species of mammals in the extant African fauna. This is essentially similar to the previous method except that the resulting indices are specific to the taxonomic levels used. T h e importance of this specificity stems from the wide range of habitat preference found in some families and higher taxonomic groups. An example of this is the Felidae, in which the genus Acinonyx fills the niche of a large diurnal predator in grassland, one species of the genus Panthera is found over a great range of habitats while the other is associated with forest or woodland-bushland, and within the genus Fells, four species are found in woodland-bushland, one in forest, one in arid environments and one in grassland. Each of these genera, and the family as a whole thus have their own specific ecological range, and the identification of a fossil species to any one of these groups can be applied to that range rather than to a general or arbitary range taken from any one species. The actual habitat preferences of all living mammals in Africa were assessed using data from Meester & Setzer (1971) and Kingdon (1971, 1974). The habitats were divided into five types: forest, woodland-bushland, grassland, desert and semi-desert, and aquatic or swamp environments. Each species was given a m a x i m u m possible score of 1.00 which was broken down according to the habitat preference of that species, so that if an animal occurs in more than one habitat type, it was scored proportionally according to its habitat preference. For example, the African elephant, which is very wide ranging, was scored 0.33 forest, 0"33 woodland-bushland, 0.23 grassland and 0.11 semi-desert. M a n y species of primate, on the other hand, were scored 1.0 forest. Scores for higher level taxonomic categories were calculated by counting the individual species scores of all contained species. For example the indices of all the species in one genus were added together and divided by the n u m b e r of species in that genus, and this provided a generic habitat index. T o obtain an index for a family, again, the indices of all its

103

MIOCENE PALAEOECOEOGY IN KENYA

species w e r e a d d e d t o g e t h e r a n d d i v i d e d b y t h e n u m b e r o f species in t h a t f a m i l y . T h e h i g h e r o r d e r indices g a v e a n e q u i v a l e n t to the fossil s i t u a t i o n w h e r e t h e species a n d often the genera are extinct. T h e n e x t s t a g e was to t a k e t h e e n t i r e f a u n a l list o f a m o d e r n c o m m u n i t y f r o m a d i s t i n c t h a b i t a t t y p e a n d e n t e r t h e indices for all o f its species, first at species level, t h e n for g e n e r a , a n d finally t h e families. T h e localities c h o s e n w e r e a m o n g t h o s e listed in A n d r e w s , L o r d & N e s b i t E v a n s (1979) to e n a b l e results f r o m t h e t w o m e t h o d s to b e c o m p a r e d . T h e t a x o n o m i c h a b i t a t indices for 11 localities w e r e c a l c u l a t e d a n d t h e results for t h e f a u n a s o f t h e s e m o d e r n localities a r e s h o w n in T a b l e 1. Table 1

T a x o n o m i c h a b i t a t i n d i c e s f o r 11 m o d e r n m a m m a l c o m m u n i t i e s

Forest

Woodlandbushland

Grassland

Semi-desert

Aquaticswamp

Specms Genus Family

0"34 0'43 0"36

0"40 0"46 0"48

0'12 0"06 0"12

0"04 0-03 0.03

0"10 0'02 0-0l

Species Genus Family

0'57 0"50 0"38

0"20 0"33 0"40

0"10 0"08 0"09

0"02 0"01 0"05

0"11 0'08 0"08

Species Genus Family

0'68 0"66 0'46

0'21 0"23 0"37

0'03 0"05 0-10

0

0'05 0"03

0'08 0"01 0'04

Species Genus Family

0"44 0'38 0"31

0"32 0"39 0"45

0" 12 0" 13 0"16

0 0"06 0"05

0"12 0"04 0"03

Species Genus Family

0'04 0"13 0"24

0"59 0'67 0'50

0"22 0'16 0'16

0"12 0"03 0"07

O-O3 0"01 0"03

Tsavo

Species Genus Family

0"04 0"13 0'27

0"53 0"60 0"47

0'21 0"15 0-16

0" 15 0"08 0"04

0"07 0"04 0"06

Jebel Mara

Species Genus Family

0'02 0'09 0'22

0'43 0'49 0"49

0"22 0"23 0"13

0"30 0" 15 0"14

0"03 0-04 0"02

Species Genus Family

0"10 0"14 0"24

0'54 0"59 0"48

0"24 0"14 0"14

0"03 0'02 0"04

0"09 0"1t 0"10

Species Genus Family

0 0'05 0"16

0'53 0'63 0"58

0'32 0-25 0"16

0"15 0"06 0'09

0 0"01 0"01

Species Genus Family

0"09 0" 12 0"20

0"52 0"50 0"49

0"32 0"28 0-I 6

0"03 0"03 0'04

0"04 0'07 0"1I

Species Genus Family

0"20 0'31 0'34

0"48 0"49 0"44

0"15 0"13 0"14

0"09 0:05 0"04

0'08 O'O2 0'04

Deciduous forest-woodland Amani

Semi-deciduousforest Budongo

Evergreenforest Irangi

Montane forest Semliki

Woodland Banagi

Bushland

Bushland grassland Rwenzori

Grassland Serengeti

Floodplain grassland Kafile

Floodplain with forest Tana

104

E . M . NESBIT EVANS

This method was then used for fossil Miocene faunas which were analysed at the lowest taxonomic level possible. For example Rhynchocyon, an extant genus also recognized in the fossil record, was scored for genus, not family or order, but most of the other fossil insectivores belong to extinct genera and can only be analysed at the family level. The results were compared with those from the modern communities. The habitat indices of families which do not occur in Africa today, e.g. Ochotonidae, were calculated from the habitat preferences of species living in other continents. Reliable data for the Soricidae were only available for East Africa (Kingdon, 1974) and bats were excluded from the lists as they are so rarely found fossil and the modern data was to be used for interpretations of fossil environments. It is not possible to include the data in this volume due to lack of space, but they are available in the archives of the British Museum (Natural History), London.

Ecological Diversity Species diversity of mammalian communities shows distinctive patterns when analysed by various ecological and taxonomic categories. Fleming (1973) developed ecological diversity spectra and indices for analysis of the structure of modern forest communities, and Andrews et al. (1979) applied this technique to 23 present-day African communities, showing that the structure of African mammalian communities is similar in similar habitats regardless of variations in taxonomic constitution. The mammals from these communities were classified in terms of size, feeding type and locomotor type, and taxonomic constitution (at the ordinal level), and five community types from lowland forest, montane forest, grassland, floodplain, and woodland-bushland habitats were each found to have characteristic and different spectra. Similarities and differences in community structure are more dependent on the plant growth forms and thus the niche structure than on the taxonomic affiliations of the resident species, so that, for example, it is the similarities in the niche structure in the various tropical forest ecosystems that give rise to the similar pattern of ecological diversity in their mammalian communities. Forest and savanna mammalian communities have quite different spectra which make it possible to distinguish between these two biomes even in altered fossil faunas. Tropical forests are characterized by small ground dwelling, scansorial and arboreal mammals which eat the fruit and soft vegetation found in abundance in these relatively nonseasonal, evergrowing communities. Savannas, on the other hand, are characterized by large, ground dwelling mammals which primarily eat hard browse and/or grass. The relative independence of ecological diversity analyses from taxonomic groupings of the communities is of great advantage in assessing fossil faunas, which may be entirely composed of extinct species. Provided the ecological categories listed above can be identified for the fossils, it is possible to obtain ecological diversity distributions comparable with those of living communities even though they have no species in common. It is also possible to test these patterns for similarity with, or differences from, living communities, to make allowance for biases that may be known fi'om other evidence to have been introduced into the fossil faunas. In Figure 1, bats, which are rarely preserved as fossils, have been removed entirely from the analysis; and carnivores which are underrepresented in the fossil record because of their lower population numbers, are shown in Figure 1 with a two-fifth reduction in diversity as occurs in modern bone assemblages (Behrensmeyer, pers. comm.). In addition, it is also possible to introduce size bias, such as excluding given proportions of species of certain size classes, or to introduce simple

MIOCENE PALAEOECOLOGY

Figure 1. Ecological diversity spectra for the means of 23 modern African mammalian communities. The community types are given on the left together with the mean number (NM) of species for M communities. The vertical axis shows the % number of species. Four types of analysis are shown: the taxonomic composition of the faunas at the level of Order: the size distribution of the communities; the locomotor adaptations classified on a zonal basis: the zones range from purely terrestrial (LGM) ; to partly terrestrial merging into the lowest strata of vegetation cover such as ground vegetation, low bushes and fallen trees (SGM); then to scansorial and arboreal in the middle and upper tree canopies; and finally to aerial; and lasdy the feeding adaptations in the communities. Bats are omitted from the analyses and the solid bars show the results of a two-fifth reduction in the number of carnivore species. The dashed line shows the pattern with all carnivores included.

~

forest NM = 67

M=8 Montane forest N M =64 M=3 Flood -

plam =

Taxonomic order

IN KENYA

Size coteq;lory

40 3O 2O I

105

Locomotor 0doptotion

iL

40 30

L

20 I

F"!

40

L

20

I

Woodland- 50 bushland 40 ~

!

Short grass 50

r- I

plains N M =39 M=I

40

3O 20

,g

Fe~lir~ odoptotion

L k L II. kg

r a n d o m biases b y r a n d o m l y e x c l u d i n g various p r o p o r t i o n s o f the fauna. T h i s is b e i n g d o n e for c e r t a i n o f the faunas (Dreyer, in prep.) w i t h r e d u c t i o n o f f a u n a l size d o w n to o n e - t h i r d o f the c o m p l e t e fauna, a n d it a p p e a r s t h a t such r a n d o m r e d u c t i o n s have r e m a r k a b l y little effect on t h e ecological diversity patterns. This removes a l i n g e r i n g d o u b t t h a t fossil faunas, w h i c h m u s t always be assumed to be i n c o m p l e t e a n d w h i c h h a v e species n u m b e r s well b e l o w those o f living communities, can b e c o m p a r e d d i r e c t l y w i t h living faunas.

Socioecology J a r m a n (1974) d i v i d e d t h e living A f r i c a n bovids into five categories based on t h e i r feeding b e h a v i o u r , m o r p h o l o g y , social b e h a v i o u r a n d h a b i t a t preferences. J a n i s (1980) suggests t h a t it m a y be possible to identify these categories m o r p h o l o g i c a l l y a n d thus p r e d i c t the socioecological categories a n d h a b i t a t s o f fossil species. T h i s m e t h o d , i f used alone, has the defects i n h e r e n t in the use o f " i n d i c a t o r species". H o w e v e r , w h e n used t o g e t h e r w i t h o t h e r m e t h o d s discussed here, this can be a useful a d d i t i o n a l tool. T h e r e l a t i v e a b u n d a n c e s o f a n i m a l species w i t h i n a c o m m u n i t y can give v a l u a b l e i n f o r m a t i o n a b o u t the structure o f the c o m m u n i t y a n d the h a b i t a t . F o r e x a m p l e , A n d r e w s (1973) showed t h a t r o d e n t faunas o f open w o o d l a n d a n d grassland h a b i t a t s a r e

!06

E.M. NESBIT EVANS

dominated by single species which may make up as much as 80-90 ~o of the total rodent population. However the rise of these kinds of data in the fossil record can be misleading. Relative numbers of animals in the fossil record may reflect many things other than species dominance in the living community. Wolff (1973) developed a list of these, some of which are (1) predator actions or preferences, (2) habits, (3) reproductive rate, (4) size, (5) life span, (6)mortality characteristics, (7) burial and depositional environments. However, certain extremes in relative abundance must relate to ecological preferences and actual population density differences. At present, these sorts of differences must be used with extreme caution.

3. Songhor The Early Miocene fauna from Songhor, which is tile first of the fossil faunas analysed here, is rich in diversity of species and also in numbers of individuals, with some excellent forest indicator species. The best examples of these are anomalurid flying squirrels (three species of Paranomalurus) two species of the elephant shrew Rhynchocyon, three species of prosimians and a tenrecid (Pickford & Andrews, this volume). The fauna is also remarkable in having only eight species of artiodactyl. The tragulids and allied forms are low in diversity, but two of them, Dorcatherium songhorensis and Walangania africanus are relatively common. The number of insectivores is particularly high, and they are most abundant in Bed 9 of the Songhor sequence (Pickford & Andrews, this volume). Nine species of primate occur in the fauna, of which Limnopithecus legetet and Proconsulgordoni are the most numerous. In modern communities, this number of primate species is only found in full forest situations; woodland-bushland or grassland communities have far fewer species. A further confirmation that Songhor was probably forested is found in the relative proportions of rodent species. The most abundant species, Diamantomys luederitzi makes up 52% of the numbers of individuals of rodent species, and several other species have moderately high proportions, a pattern that is characteristic of modern forest communities (Andrews, 1973). The habitat spectrum of the Songhor fauna is shown in Figure 2(a). It shows that the highest values are for forest elements in the fauna, tbllowed by woodland and woodedgrassland and finally grassland bushland and desert in decreasing order. This is due to the heavy weighting which the forest species carry. The taxonomic habitat index [Figure 2(b)] also emphasizes the importance of forest, with a lower index for woodlandFigure 2. Songhor habitat spectrum (a) and taxonomic habitat spectrum (b). Symbols are F, forest; W, woodland; B, bushland; G, grassland; SD, semi-desert, D, desert; A, aquatic. The complete fauna known from Songhor (N 64) is analysed here.

9O 8o

(a)

7O 60 50 40 30 20 I0

(b)

0'6 -'~~

0"5 K 0.4 0-3 L 0"2 O.I F W WG G B D A F WB G SD A

MIOCENE

PALAEOECOLOGY

107

IN KENYA

Figure 3. Ecological diversity analyses ofthe 1972 Songhor collections from Bed 5 and from all levels. Numbers of species are shown on the left (N). Classesand explanation are the same as in Figure I. %

Toxonomic

order

Size category

Locomotor odoptotion

Feedinq odoptotion

50 Songhor

40

197:> coil" N = 55

30 2O 10

Songhor

50

k.L .

bed 5, 1972 4 0 col lection 30 N= 25 20 10

o~ >o ~='~

~ >

o

T --

,,, ,,,, J~<[u)

._~> ~ o o o


kg bushland animals, differing from the habitat spectrum in the low emphasis on the grassland part of the fauna. The pattern of community structure of the Songhor fauna analysed by ecological diversity is shown in Figure 3. It is most similar to that of modern forest faunas (Figure I) and in the statistical tests the correlation coefficients of the Songhor and the present day lowland forest patterns are statistically significant (P = 0"05) in three out of the four analyses (Andrews et al., 1979); in the taxonomic category the highest correlation was also with the lowland forest pattern, but it was not significant. T h e Z~ tests similarly showed the Songhor pattern to be different at a high level of significance (P = 0.001) from modern woodland-bushland and grassland communities in six cases, and at a lower level of probability (P = 0"05) in another two cases (Andrews et al., 1979). Results for faunas for a single level and for all levels combined are shown in Figure 3, and both collections show broadly similar patterns in the four analyses, with high proportions of rodents and primates in the first, high proportions of small m a m m a l s in the second, high proportions of the small ground m a m m a l s (SGM) and arboreal classes in the third and high proportions of frugivores and insectivores in the fourth. T h e difference between the faunas can be accounted for by the fact that the fauna from all levels at Songhor includes the Bed 9 fauna, which is particularly rich in insectivores, whereas the Bed 5 fauna analysed on its own has lower proportions of insectivores. This shows up particularly in the taxonomic and feeding categories in Figure 3. An examination of the community structure in terms of ecological diversity spectra suggests strongly the presence of forest. A large number of the mammals are arboreal requiring the presence of arboreal throughways. Frugivores and soft-vegetation browsers dominate in the feeding class and require the presence of ever growing fruiting and leafing bodies. The large numbers of small insectivores must also live in forest where their prey

108

E.M. NESBIT EVANS

are abundant and present non-seasonally. The abundance of small mammals is characteristic of forest communities , in particular the dominance of rodents. This evidence is in agreement with the analyses of indicator species, habitat spectra and taxonomic habitat indices, and it clarifies any ambiguities arising from these less precise methods. Tropical rain forest was clearly the main habitat from which the Songhor fauna was derived, and the terrestrial nature of the deposits and the absence of any sedimentary evidence of water action suggests that the fauna was largely autochthonous (Pickford & Andrews, this volume), so that it is probable that the palaeoecology of the Songhor area was dominated by forest. On the other hand there is evidence for a size bias in the Songhor fauna, with large animals underrepresented, and this m a y be the result of carnivore activity (Pickford & Andrews, this volume) which may have introduced a bias into the present analysis. 4. K o r u

The Koru faunas will be considered in three units, the K o r u Formation, the Legetet Formation and the K a p u r t a y Agglomerates exposed at C h a m t w a r a (Pickford & Andrews, this volume). The fauna from the Koru Formation is small (N = 26), and there are no good indicator species present. T h e lack of forest indicator species is particularly noticeable when this fauna is compared with the faunas from the Legetet Formation and Chamtwara. At Legetet the fauna is larger (N = 37) and there are a number of forest indicator species, including two species of Rhynchocyon, and three species of anomalurid. There is also a great variety of rodents and the most common species, Diamantomys luederitzi, makes up under 50% of the number of individuals found. At Chamtwara, the size of the fauna is slightly larger than at Legetet (N = 39) and the forest indicators there are the same as those at Legetet with the addition of another species of anomalurid. There is a high diversity of rodent species with the most numerous of these again making up well under 50% of the rodent specimens. Both Legetet and Chamtwara faunas resemble the Songhor fauna in the presence of these indicator species. The habitat spectra for the C h a m t w a r a and Legetet faunas are very similar, showing highest proportions in the forest category, with slightly higher proportions for Legetet than Chamtwara (Figure 4). This difference is difficult to explain in terms of indicator species or the other methods discussed in this section, for all of the most heavily weighted animals such as Rhynchocyon, which is an extant genus, occur in both faunas. The habitat represented by the fauna of the K o r u Formation is not easy to interpret; forest and woodland categories are equal and the total savanna habitat spectrum is considerably Figure 4. Koru habitat spectra for the faunas from the three main fossiliferous horizons, the K o r u Formation on the left, the Legetet Formation in the middle and the C h a m t w a r a M e m b e r of the K a p u r tay Agglomerates on the right. Faunal sizes are for Koru, N -- 26, for Legetet, N = 37, and for Chamtwara, N = 39. Symbols are as in Figure 2.

60

Koru

Legetet

Chamtwara

50 40 30 20 10 F W WG

G

F

W

WG G

F W WG

6

MIOCENE PALAEOECOLOGYIN KENYA

109

Figure 5. Koru taxonomic habitat spectra for the same three faunas analysed in Figure 4. Symbolsas in Figure 2. 0.6

Koru

C hamtwara

Legetet

0"4 0.3 0.2 0"1 F WB

G

SD

A

F WB

G

SO Aq

F WB

6

SD A

larger when grouped than that for forest. Although the low number of species from the Koru Formation must be borne in mind, it is possible that the habitat during deposition was more open than that of the Legetet Formation or Chamtwara, although all appear to have been primarily forest. The taxonomic habitat indices for the Legetet and Chamtwara faunas are very similar in all the categories and closest to forest; the Koru Formation fauna is also predominantly forest, but has a relatively higher value for woodland-bushland. The results are in close agreement with those of the habitat spectra (Figures 4 and 5). In comparing these values with those from the modern habitats (Table 1), the greatest similarity is seen with the figures for semi-deciduous forest (Budongo) rather than evergreen or montane forest, and the values are unlike those from bushland, grassland or floodplain, but the small samples here and the fact that the calculations for taxonomic habitat indices were done at mixed taxonomic level must be taken into account. In the ecological diversity analyses, the Legetet and Chamtwara faunas are both structured like modern forest communities (Figure 6). They are dominated by small ground dwelling mammals with fairly high proportions of arboreal, scansorial and aerial types. In addition, frugivores and browsers, which require ever-growing plants, dominate the feeding category together with insectivores. The Koru fauna on the other hand has an unusual community structure. The locomotor category is fairly typical of savanna Figure 6. Ecological diversity analyses of the same three Koru faunas analysed in Figures 4 and 5. Classes and categories as in Figure 1.

% 60

50 40 30

]o 6O

5O 4O :5O 2O I0

Taxonomic order

Size cateqory

Locomotor adaptation

Feeding adaptation

Koru

, . . u k .L Legetet

L LI..

L IlL =hl_

60 50 Chamtwara

2O 10 R I PAC

0

ARC DP'FGH

LGM ~J'b Aq SGM S Aer

I FHbHgCO

110

E. M. NESBITEVANS

faunas, but unlike savanna communities there are numerous browsers, some frugivores and no grazers, and there is a dearth of mammals in the i0-45 kg category. When these three faunas are compared with the modern communities (Figure 1), the Chamtwara and Legetet faunas show closest resemblance with forest habitats, but proportions of artiodactyls and carnivores are lower than would be expected. The Koru Formation fauna bears no resemblance at all to any of the modern faunas. In the size categories the Legetet and Chamtwara faunas have parallels with montane forest due to the high proportions of small mammals, although this may equally be the result of the low number of artiodactyls. In summary, most of the evidence presented here suggests that the faunas from Chamtwara and the Legetet Formation were similar both ecologically and taxonomically. Their structural similarity with present day forest faunas makes it most probable that the habitat of the fauna was forest, possibly resembling montane forest to a great extent. As at Songhor, the sedimentary environment with which the fossil faunas are associated indicate terrestrial conditions, but also like Songhor, there is evidence for a size bias against the larger animals which may have affected the palaeoecological conclusions reached here.

5. Karungu and Rusinga Unfortunately it has not been possible to provide the data for the rich Miocene faunas from Karungu and Rusinga Island. Two faunas only can be mentioned here, a fauna from Kaswanga Point in the Hiwegi Formation of Rusinga Island described by Andrews & Van Couvering (1975) and a fauna excavated by Andrews from Bed 16 (Oswald, 1914) at Karungu. Both these have been mentioned previously by Andrews et al. (1979). The Rusinga fauna includes a number of forest indicator species, including Rhynchocyon and anomalurids. It is from the same formation, although from a different level, as the majority of the plant remains described by Chesters (1957). As already mentioned, the flora indicates a forest habitat also. The Karungu fauna on the other hand is one of the few from the Early Miocene faunas of East Africa to indicate non-forest conditions. It is dominated by ochotonids and macroscelidine elephant shrews, both with extremely hypsodont teeth suggesting a grazing adaptation and thus indicating an environment where coarse ground vegetation was dominant. Such an environment would be unlikely to occur in a forest situation except possibly at the edge of a swamp where grasses and sedges were common. Figure 7. Taxonomic habitat spectra for faunas from Karungu (Bed 16, N = 16) and Rusinga (below marker bed 1 faunas for Kaswanga Point, Hiwegi Formation N = 31). Symbols as in Figure 2.

0.60 0.50

Korungu

0.40 0.30 0.20 0.10 F W.B

G S'D A

Rusinga

IU F W-B

G S'D A

The analysis of the taxonomic habitat indices produced a spectrum for the Rusinga fauna that supported the forest affinities of the indicator species (Figure 7). The Karungu fauna, on the other hand, has an ambiguous pattern divided equally between forest and

MIOCENE

PALAEOECOLOGY

1 11

IN KENYA

woodland-bushland. In the ecological diversity analyses (Figure 8) both faunas have peculiarities in community structure that make it difficult to draw parallels with modern faunas, especially Karungu, which, on this evidence must remain uncertain for the present. T h e Rusinga community structure is certainly close to that of the extant forest faunas, but the statistical tests gave no significant results and the pattern differs in m a n y Figure 8. Ecological diversity analyses of the same two faunas from Rusinga and Karungu analysed in Figure 7. Classesand categories as in Figure 1.

%

Taxonomic order

Size category

Locomotor adoptot=on

Feeding ocloptotion

Rusingo 40 below I 30 N=31 Korungu 40 bed 162030[ N = 15 10 co

~ . ~ E~

o,_,o

-- T - : - ~ - -

-~g_~ _ ~ ~

~E2oo~

c.

.>_~a~o |

kg respects from those of any of the living communities. Both faunas are associated with floodplain sedimentary environments, and we conclude that the bias introduced by hydrodynamic sorting m a y have so altered the faunas as to make them useless for palaeoecological interpretation.

6. M a b o k o The Maboko fauna is sparse, with only 32 species, and the affinities of the two most abundant species, the monkey Victoriapithecus macinnesi and Climacoceras (Andrews et al., this volume) are uncertain. Climacoceras was probably a soft browsing forest to woodland dwelling artiodactyl, while the two bovids, Eotragus and another non-boselaphine bovid (often listed as Gazella) m a y have been adapted to harder browse and were most likely woodland dwellers. T h e abundance of monkeys is puzzling, and if it indicates anything it must suggest the presence of trees. In completely open habitats today, it is rare to find more than one primate species and it is not all that common to find two species, this being more usually a feature of forest habitats. Two species are certainly present at Maboko, and one of them has some adaptations for at least a semi-terrestrial habitat (Delson, 1975) suggesting a possible woodland-forest ecotone, although the complete absence of other forest indicator species suggests that woodland predominated in the environment. The low numbers of small mammals indicates a possible taphonomic size bias in the fauna, although the rest of the fauna shows no signs of being transported and it seems reasonable to assume that m u c h of the Maboko assemblage is autochthonous. T h e presence of water near the site is shown by crocodiles, chelonians, frogs, fish and wading birds, and this is confirmed by sedimentological evidence which suggests the existence of a flood plain, ranging from extremely wet at the southern Maboko exposure and drier to the north at Majiwa and Kaloma. Supporting evidence for this interpretation

112

E.M. NESBIT EVANS

is also found in the overall similarity of the faunas from Majiwa and Kaloma, which mainly differ from the Maboko fauna in having more land gastropods. T h e combination of Homorus, Burtoa, Limicolaria and some streptaxids found at M a j i w a / K a l o m a is typically found in modern thick riverine woodland-bushland; and the aquatic elements so common at Maboko are rare or absent at these sites. The habitat spectrum for Maboko is shown in Figure 9 together with the spectrum for the taxonomic habitat index. Both methods are in agreement in the emphasis of the results on forest and woodland, but the grassland element of the fauna shown by the taxonomic habitat index is less emphasized than that in the habitat spectrum. T h e relatively small fauna makes analysis by ecological diversity methods unrealistic. It may Figure 9. Habitat spectrum (a) and taxonomic habitat index (b) for the combined Maboko Formation fauna (N = 32). Symbols as in Figure 2.

80 70 60 50 40 30 20 I0 RF W WG G

F W'B

G S'D A

be concluded that the faunal remains at Maboko, Kaloma and Majiwa indicate a thick woodland, perhaps verging on forest, although there is no direct evidence for the presence of forest. Sedimentological evidence showing changes in degree of wetness of the floodplain sediments correlates with the increasing scarcity of the aquatic faunal elements in Majiwa and K a l o m a to suggest that the sites, which extend over a distance of about 2 km, are sampling a wooded floodplain with dense woodland and/or riverine forest. 7. F o r t T e r n a n

The two most common species in the Fort Ternan fauna are the bovids Oioceros tanyceras and Protragocerus labidotus which make up 52% of the fauna (Shipman et al., this volume; Gentry, 1970). Using scanning electron microscope techniques, Shipman et al. (this volume) believe Oioceros to be a mixed feeder, preferring grass, while the teeth of the bovid, Pseudotraguspotwaricus are sub-hypsodont, a type of dentition which is also associated with mixed feeders. Another grassland indicator is the occurrence of the ostrich, Struthio. Much less commonly represented in the fauna are the forest indicator species such as anomalurids, a lorisine and a rhynchocyonine. The dryopithecines, which have also been used as forest indicator species, show evidence of rolling and water transport (Shipman et al., this volume), suggesting that they may be derived from other habitats. Habitat spectra for most Late Cenozoic East African sites suggest a change in local habitat from a predominant rainforest biome in the Early Miocene to a predominant savanna biome in the later Miocene (Van Couvering, 1980). T h e Fort Ternan habitat spectrum [Figure 10(a)] is one of the earliest known which suggests the presence of a savanna biome. T h e spectrum constructed on species lists alone suggests the presence of a combination of rainforest and savanna biome, with a predominance of woodland

113

M I O C E N E P A L A E O E G O L O G Y IN K E N Y A

c o m m u n i t y types in the latter. T h e spectrum based on the relative abundance of species suggests that the savanna biome is dominant with a minor amount ofrainforest. In Other faunas for which both types of spectra have been drawn the species list and relative abundance spectra are m u c h more similar (e.g. Maragheh; Campbell et al., in prep.). The dichotomy between these two spectra at Fort Ternan suggests that either the Fort T e r n a n assemblage is derived from an environment not sampled in Africa today, or that it was a rain forest-woodland-savanna ecotone. The abruptness of the change in habitat necessary to give such an ecotonal association is found today, for example, where the moist-dry faces of mountains meet or where edaphic conditions are controlled by flooding (Andrews et al., 1975). The taxonomic habitat indices are similar to the results for the habitat spectra [Figure 10(b) ]. This method fails to take into account relative densities of the species so that the Figure 10. Habitat spectra (a) and taxonomic habitat index (b) for the Fort Ternan fauna, all levels combined (N = 45). Symbols as in Figure 2 and see text for explanation.

70 60 50 40

50 20 I0 F

W WG G

B

D

A

F WB G

SD A

rare species such as the forest indicating lorisines and anomalurids, which are represented by single specimens, are given equal weight to the much more numerous bovid species. We have tried to allow for this in Figure 10 by multiplying the taxonomic scores by the percentage representation of the animal (in terms of m i n i m u m numbers) in the fauna. This can be seen to have resulted in approximately equal proportions of forest and woodland animals, with everything else much less well represented (Figure 10). In 1979 Andrews, Lord and Nesbit Evans produced an interpretation of the Fort T e r n a n fauna based on an ecological diversity analysis of the faunal list then available. This has been updated by additions to the list based on recent identifications by ourselves and by Drs P. Shipman, P. M. Butler and R. Lavocat, so that the m a m m a l i a n species total for all levels at Fort T e r n a n is now 45 (Shipman et al., this volume). T h e results for this method are given below (Figure 11), using these new data. Size spectrum. The size spectrum of the Fort T e r n a n palaeocommunity is peculiar, not in the low numbers of small m a m m a l s in general, as was shown by Andrews & Nesbit Evans (1979), but by the dearth of m a m m a l s in the 1-10 kg category. None of the modern spectra shown by Andrews et al. (1979) show this phenomenon. Small-sized m a m m a l s are severely underrepresented in m a n y fossil assemblages and in some modern bone assemblages (Behrensmeyer et al., 1980). In general small bones are more easily destroyed by the environment and small mammals are often taken from the living assemblage at death because, unlike larger animals, they are eaten whole. However these factors do not explain the fact that while 30% of the species at Fort Ternan are less than t kg in size (and 40% of these are represented by three or more species), only 13 % of the

1 14

9 E. 3.,I. N E S B I T

EVANS

m a m m a l s are in the 1-I0 kg category. Animals which ordinarily fall into this size category in extant and fossil African faunas are lagomorphs (none), large rodents (one), small carnivores (one), small ungulates (one), monkeys (none), small hyraxes (none), small "apes" (one). The absence of monkeys and small carnivores seems to be an important factor here. The presence of a fairly large number of m a m m a l s in the less than 1 kg category suggests that the dearth of 1-10 kg mammals is real (that is, reflects the situation in the living community) rather than due to taphonomical or sampling errors. Locomotor spectrum. T h e locomotor spectrum is unambiguously similar to that seen in all of the community types analysed from the savanna biome: large ground mammals ~176

Taxonomic order

Size category

50

~

~

50

_ l

l--1

l l. Ecological diversity analysesoftwoFortTernanfaunas, that from bed 6 alone and that from all levels as in Figure 10.

Fort Ternan 4 0

Classes and categories as in Figure

bed 6

Figure

1

--28

Locomotor adaptation

1 L

Feeding adaptation

~.~

~

5O

&h L

Fort Terpzln : ~ N : 45 20 10

o~ -_-

-~

~ o

m ~ E.o ~. w

0

~ 0770

_T_~C0

o----O'~ A

"6

~

g ~-~c:oo

.Au),~o~ ~

u~lll ~N

~'9,

22

~ ~ | '~ |174

.-.-_. . . . ~ cp~

"~'~.

--cu. T I O o

kg

dominate, small ground m a m m a l s are secondary and there is a dearth of other locomotor types. This reflects not only the presence of more large mammals but also the increase in terrestriality, probably due to the absence of layered canopies of the rainforest biome which provide throughways in the trees for upper stratum animals. It is important to note that there are no aquatic m a m m a l s or other vertebrates known from Fort Ternan, with the exception of a single fragment of crocodile bone. This strongly suggests that we are not dealing with a floodplain environment. Feeding spectrum. T h e feeding spectrum of the Fort Ternan palaeocommunity is intermediate between that of modern rainforest and savanna biomes. In comparison with the rainforest spectra, Fort Ternan has few insectivores and frugivores and is thus more similar to the extant savanna blame. However, the browser :grazer ratio is about 2:1, while that of a modern s a v a n n a is about 1 : 1 and that of a modern forest is 2 or 3 : I. A more detailed analysis of the feeding categories shows that among the browsing herbivores, almost 20 ~ would be likely to rely on the presence of new growth and budding and fruiting bodies of plants (these herbivores can be termed soft browsers), while about 12 % rely on leaves alone (hard browsers) and 11% on leaves and grass (mixed feeders). This emphasis on soft vegetation is unlike that found in a modern savanna blame and

M I O C E N E P A L A E O E C O L O G Y IN K E N Y A

115

demonstrates the presence of only moderate seasonatity. In extremely seasonal environments, such as exist in modern savanna biomes, new growth is present only seasonally, and this new growth is not nearly as succulent as that of forest plants due to the development of specialized features which protect it from dessication. Shipman (this volume) disagrees with the interpretation of the larger fauna (N = 45) and finds that the Fort Ternan fauna is strikingly similar to a grassland or floodplain fauna. She also suggests that this method is sensitive to even small increases in sample size which may significantly alter the results, but we have found by the analysis of random selections of modern faunas (see Section 2) that samples of only one-third of the total fauna still reflect the community structure of the total fauna at least within the limits used here.

Socioecology. Many ungulates, particularly antelopes, can be placed in Jarman's (1974) socioecological categories on the basis of morphological features (Janis, in prep.). An analysis of the Fort Ternan antelopes using Janis' morphological criteria shows that (1) Eotragus, Gazella, and Protragocerus, which are small, sexually dimorphic and have limbs of average length probably lived in small groups with territorial males and had a small home range (Jarman's Class B); (2) Oioceros, which is similar morphologically to the above three but has somewhat more flamboyant horns in the males may belong to Jarman's Class C in which case it would occur in larger groups (6-60), have a fairly large home range and have only seasonally territorial males; (3) Pseudotragus, which is somewhat larger, not sexually dimorphic and has relatively long limbs probably belongs to Jarman's Class D and thus may have lived in moderately large to very large groups (6-600) had a poorly defined home range, have been seasonally migratory and have had seasonally territorial males. The more primitive non-bovid ruminants would all fall into J~trman's Class A; they would have lived singly or in pairs, had a small home range and have been territorial. The only herbivore truly indicative of seasonality is Pseudotragus and it is not abundant at the site (8 individuals; 94 specimens). The giraffids are difficult to evaluate and are not included in the above remarks. In general the socioecology of tile ruminants is indicative of mammals living in closed to moderately closed habitats (Jarman, 1974).

Palaeoecology of the Fort Ternan assemblage. The taphonomical analyses of Shipman (this volume) presented above, show fairly clearly that the Fort Ternan assemblage is, for the most part, untransported and quickly buried and thus is, in essence, an autochthonous assemblage. After removing those taxa which are represented by a high percentage of abraded bones, and thus thought to be intrusive, the Fort Ternan fossil assemblage can be considered to represent much of the living assemblage of that particular time and space and will be treated here as a palaeocommunity. The Fort Ternan palaeocommunity is dominated by mammals which use terrestrial throughways; eat browse, especially soft-browse; are small to medium in size; within the ruminants, are territorial, sexually dimorphic and non-migratory. In addition the fauna consists predominantly of herbivorous terrestrial mammals of all sizes, but especially greater than 10 kg. The locomotor diversity is low ( H - - 64) and feeding and size diversities are high (91 and 95, respectively). The dominance of the fauna by woodland species indicates that there were large areas of woodland and perhaps wooded grassland, but the presence of a small percentage of forest-dwelling species, some of which show signs

116

E . M . NESBIT EVANS

of being transported, suggests that there were also forested areas near the site. It is possible that the forest was concentrated on highland areas or on the windward sides of hills close to the site in a pattern of forestation common in East Africa today, while the lowland areas were most likely a mosaic of riverine gallery forest, woodland and savanna. In general, this palaeoeeological reconstruction agrees with the scenario presented by Andrews & Walker (1976). 8. C o n c l u s i o n s

The Early Miocene mammalian communities of Western Kenya which we have studied here are primarily forest communities, especially those from Songhor, Koru and Rusinga. Some faunas from specific levels, such as those from Karungu, the Koru Formation and locality K H at Rusinga (Andrews & Van Couvering, 1975), may represent somewhat more open habitats. There is an apparent change between these sites and the later ones, first indicated at Maboko, but both the dating and the palaeoecologieal interpretation of the Maboko faunas are open to debate. Fort Ternan is the earliest example in East Africa which is well substantiated and shows a marked change in habitat and community structure towards more open, wooded habitats. This habitat, however, and the structure of its palaeocommunity, is not like those of the present day savanna habitats which are dominated by wooded-grasslands, but is more woodland dominated, combined perhaps with some forest in wetter areas. This difference may arise from man's recent impact on the African landscape which has resulted in the destruction of most of the wooded areas as these are prime agricultural areas. The later and less wooded savanna communities at Pikermi, Samos and Maragheh have not yet been studied in detail, but should give us an understanding of a highly developed savanna in which woodland and woodedgrassland are more equal components. Hominoid primates, and in particular ramapithecines, are important in the woodland dominated savanna communities of Turkey, Pakistan and China as well as Kenya, but they do not occur in the more open savanna communities. Later still, however, the earliest hominids are found associated with these wooded-grassland dominated communities in the Pliocene (e.g. the O m o and East Turkana sites). Continued work on the taphonomy and palaeoecology of these hominoid bearing sites will enable us to describe better the place of these animals in their communities, their adaptive shifts and the community succession and the community evolution of the forest and savanna biomes.

The authors are very grateful for assistance received from S. Dreyer, L. Martin, M. Pickford and N. Solounias.