Savanna Corridor Research Articles

Forest mosaics, not savanna corridors, dominated in Southeast Asia during the Last Glacial Maximum.

The dominant paradigm is that large tracts of Southeast Asia's lowland rainforests were replaced with a "savanna corridor" during the cooler, more seasonal climates of the Last Glacial Maximum (LGM) (23,000 to 19,000 y ago). This interpretation has implications for understanding the resilience of Asia's tropical forests to projected climate change, implying a vulnerability to "savannization". A savanna corridor is also an important foundation for archaeological interpretations of how humans moved through and settled insular Southeast Asia and Australia. Yet an up-to-date, multiproxy, and empirical examination of the palaeoecological evidence for this corridor is lacking. We conducted qualitative and statistical analyses of 59 palaeoecological records across Southeast Asia to test the evidence for LGM savannization and clarify the relationships between methods, biogeography, and ecological change in the region from the start of Late Glacial Period (119,000 y ago) to the present. The pollen records typically show montane forest persistence during the LGM, while δ13C biomarker proxies indicate the expansion of C4-rich grasslands. We reconcile this discrepancy by hypothesizing the expansion of montane forest in the uplands and replacement of rainforest with seasonally dry tropical forest in the lowlands. We also find that smooth forest transitions between 34,000 and 2,000 y ago point to the capacity of Southeast Asia's ecosystems both to resist and recover from climate stressors, suggesting resilience to savannization. Finally, the timing of ecological change observed in our combined datasets indicates an 'early' onset of the LGM in Southeast Asia from ~30,000 y ago.

Moving Histories: Bantu Language Expansions, Eclectic Economies, and Mobilities

AbstractThis essay interprets a classification of Africa's Bantu languages which used statistical tools guided by assumptions about farming and its chronology to analyze fresh vocabulary evidence. It shows a peeling movement from Cameroon's grassfields, into southern Cameroon, then along a savanna corridor through West Central Africa's rainforests, into the Savannahs, then to Southern Africa, the Great Lakes, and Indian Ocean coast. The clear sequence of movement masks methodological and historical factors. Language death, multilingualism, and the limits of vocabulary evidence restrain the classification's authority. ‘Transformations’ from food collecting to food producing or from no metals to full engagement with metals were mutable, unfolded at different speeds, and involved interactions with firstcomers. In Central Africa, Bantu speakers were often the first farmers and metal-users in the region but elsewhere they were commonly neither. Their arrivals did not immediately displace firstcomers. Computational methods can accommodate many of these issues.

Coexistence of savanna and rainforest on the ice-age Sunda Shelf revealed by pollen records from southern South China Sea

Exposure of the presently submerged continental shelf of Southeast Asia during low sea-level stands of the Quaternary is thought to be deeply involved in the biogeographic evolution of this biodiversity hotspot. Inland proxy records are mounting to argue grassland expansions over Southeast Asia during glacial periods, lending supports to the existence of a transequatorial “savanna corridor” as hypothesized. However, pollen records retrieved from marine sediments have indicated widespread rainforests on the exposed northern Sunda Shelf. To reconcile these seemingly conflicting observations, here we present new, multisite marine pollen records from the southern South China Sea focusing on the Last Glacial Maximum (LGM) time interval. It is found that the sites in front of the Sunda Shelf palaeo-rivers contain substantially more Poaceae pollen, in particular a smaller size fraction, than the site offshore North Borneo. Among the sites, abundant lowland tree pollen with similar major taxa is also observed. The co-occurrence of grass and rainforest pollen suggests a longitudinal climate gradient with increasing aridity toward the interior of glacial Sundaland. Combining our results with various palynological evidence from marine sediments seems to indicate that the vegetation on the exposed Sunda Shelf might not be fully recognized by previous studies. This is likely due to an admixture of pollen from other source regions, particularly Borneo where the rainforest was retained during glacial periods. Therefore, the extant vegetation records, from both terrestrial and marine archives, support the hypothesis of a “savanna corridor” over the LGM sundaland.

Late Pleistocene human paleoecology in the highland savanna ecosystem of mainland Southeast Asia

The late Pleistocene settlement of highland settings in mainland Southeast Asia by Homo sapiens has challenged our species’s ability to occupy mountainous landscapes that acted as physical barriers to the expansion into lower-latitude Sunda islands during sea-level lowstands. Tham Lod Rockshelter in highland Pang Mapha (northwestern Thailand), dated between 34,000 and 12,000 years ago, has yielded evidence of Hoabinhian lithic assemblages and natural resource use by hunter-gatherer societies. To understand the process of early settlements of highland areas, we measured stable carbon and oxygen isotope compositions of Tham Lod human and faunal tooth enamel. Our assessment of the stable carbon isotope results suggests long-term opportunistic behavior among hunter-gatherers in foraging on a variety of food items in a mosaic environment and/or inhabiting an open forest edge during the terminal Pleistocene. This study reinforces the higher-latitude and -altitude extension of a forest-grassland mosaic ecosystem or savanna corridor (farther north into northwestern Thailand), which facilitated the dispersal of hunter-gatherers across mountainous areas and possibly allowed for consistency in a human subsistence strategy and Hoabinhian technology in the highlands of mainland Southeast Asia over a 20,000-year span near the end of the Pleistocene.

Plastome phylogeography in two African rain forest legume trees reveals that Dahomey Gap populations originate from the Cameroon volcanic line

Paleo-environmental data show that the distribution of African rain forests was affected by Quaternary climate changes. In particular, the Dahomey Gap (DG) – a 200 km wide savanna corridor currently separating the West African and Central African rain forest blocks and containing relict rain forest fragments – was forested during the mid-Holocene and possibly during previous interglacial periods, whereas it was dominated by open vegetation (savanna) during glacial periods. Genetic signatures of past population fragmentation and demographic changes have been found in some African forest plant species using nuclear markers, but such events appear not to have been synchronous or shared across species. To better understand the colonization history of the DG by rain forest trees through seed dispersal, the plastid genomes of two widespread African forest legume trees, Anthonotha macrophylla and Distemonanthus benthamianus, were sequenced in 47 individuals for each species, providing unprecedented phylogenetic resolution of their maternal lineages (857 and 115 SNPs, respectively). Both species exhibit distinct lineages separating three regions: 1. Upper Guinea (UG, i.e. the West African forest block), 2. the area ranging from the DG to the Cameroon volcanic line (CVL), and 3. Lower Guinea (LG, the western part of the Central African forest block) where three lineages co-occur. In both species, the DG populations (including southern Nigeria west of Cross River) exhibit much lower genetic diversity than UG and LG populations, and their plastid lineages originate from the CVL, confirming the role of the CVL as an ancient forest refuge. Despite the similar phylogeographic structures displayed by A. macrophylla and D. benthamianus, molecular dating indicates very contrasting ages of lineage divergence (UG diverged from LG since c. 7 Ma and 0.7 Ma, respectively) and DG colonization (probably following the Mid Pleistocene Transition and the Last Glacial Maximum, respectively). The stability of forest refuge areas and repeated similar forest shrinking/expanding events during successive glacial periods might explain why similar phylogeographic patterns can be generated over contrasting timescales.

Speciation Associated with Shifts in Migratory Behavior in an Avian Radiation.

Migratory animals move up to thousands of kilometers every year [1]. Losses of migration (i.e., migratory drop-offs) occur when individuals of a migratory species stop migrating and establish founder sedentary populations, a phenomenon documented in birds [2-5] and butterflies [6]. In theory, losses-and also gains-of migration might promote speciation if sedentary and migratory populations become reproductively isolated [7-9]. Because migratory and sedentary strategies involve alternative physiological, behavioral, and morphological traits [10-13], divergence along multiple axes of organismal function is expected to accompany switches in migratory behavior, potentially accelerating speciation. We present evidence of speciation driven by a migratory drop-off in the fork-tailed flycatcher (Tyrannus savana) resulting in reproductive isolation likely driven by changes in breeding schedules (allochronic speciation [13-15]) and geographic isolation of breeding grounds (allopatric speciation [16]). Phylogenetic analyses across New World flycatchers (Tyrannidae) showed that an association between speciation and drop-offs is also observable at a macroevolutionary scale. Loss of migration was significantly more frequent than its gain, and speciation rates of migratory and partially migratory lineages (i.e., species having both migratory and sedentary populations) exceeded those of sedentary lineages. Models of trait evolution indicated that partial migration is an intermediate step between migratory and sedentary states in this family. Given that partial migration is widespread across migratory animals (e.g., of all migratory birds, ca. 51% are partially migratory [5]), speciation via switches in migratory behavior might be an important yet overlooked mechanism of animal diversification.

New fossil and isotope evidence for the Pleistocene zoogeographic transition and hypothesized savanna corridor in peninsular Thailand

Despite the explanation that the present-day biogeographic boundary between the Indochinese and Sundaic subregions at the Kra Isthmus, the narrowest part of Peninsular Thailand, in relation to differences in faunal and floral composition is almost conventionally valid for many groups of organisms, the distribution limits of modern and Pleistocene mammals in this region remain unclear. Moreover, environmental factors driving the past distribution patterns in a Southeast Asian mammal community and vegetation types contributing to the controversial hypothesis of an equatorial savanna corridor in the Thai-Malay Peninsula have rarely been demonstrated due to the scarcity of data. Since the discovery of a new Pleistocene fossil site, Yai Ruak Cave in Krabi Province, mammal fossils have been recovered from infilling sediments within the Permian karsts. On the basis of our first excavation, four mammal taxa: Hystrix cf. brachyura, Crocuta crocuta ultima, Rhinoceros sondaicus, and Rusa unicolor are taxonomically identified. A preliminary biochronological age ranging from the late Middle to early Late Pleistocene for the fauna based on the presence of C. c. ultima is proposed. The occurrence of C. c. ultima in this cave also represents the southernmost record of its known distribution, thus suggesting a non-concordant southern range limit of the Indochinese species at the Isthmus of Kra, but somewhere south of Krabi, during the Pleistocene. A bulk analysis of stable carbon isotopes investigated from tooth enamel of these mammals exhibits a variety of habitats ranging from pure C3 to C4 ecosystems, implying the existence of an open grassland landscape. The serial δ18O data collected along the tooth crown heights of R. sondaicus possibly reflect no or little seasonal variation with high annual precipitation due to a major influence of both Southwest and Northeast monsoons in the region, similar to the modern climate. Unlike today, more open vegetation/forest-grassland mosaic was however dominant in Peninsular Thailand at that time. The southward distribution range of the spotted hyaena was likely limited by the discontinuous north-south savanna corridor, latitudinally separated by a transequatorial rainforest belt, starting around the northern part of Sundaland. The ecological distinction between closed and open canopy habitats in the Thai-Malay Peninsula remarkably played a major role in confining the southward distribution of some Indochinese species and in obstructing the migration of grassland-inhabiting taxa across the Sundaic subregion during the Pleistocene glacials.

Savanna in equatorial Borneo during the late Pleistocene

Equatorial Southeast Asia is a key region for global climate change. Here, the Indo-Pacific Warm Pool (IPWP) is a critical driver of atmospheric convection that plays a dominant role in global atmospheric circulation. However, fluctuating sea-levels during the Pleistocene produced the most drastic land-sea area changes on Earth, with the now-drowned continent of Sundaland being exposed as a contiguous landmass for most of the past 2 million years. How vegetation responded to changes in rainfall that resulted from changing shelf exposure and glacial boundary conditions in Sundaland remains poorly understood. Here we use the stable carbon isotope composition (δ13C) of bat guano and High Molecular Weight n-alkanes, from Saleh Cave in southern Borneo to demonstrate that open vegetation existed during much the past 40,000 yrs BP. This location is at the southern equatorial end of a hypothesized ‘savanna corridor’ and the results provide the strongest evidence yet for its existence. The corridor would have operated as a barrier to east-west dispersal of rainforest species, and a conduit for north-south dispersal of savanna species at times of lowered sea level, explaining many modern biogeographic patterns. The Saleh Cave record also exhibits a strong correspondence with insolation and sea surface temperatures of the IPWP, suggesting a strong sensitivity of vegetation to tropical climate change on glacial/interglacial timeframes.

History of the fragmentation of the African rain forest in the Dahomey Gap: insight from the demographic history of Terminalia superba

Paleo-environmental reconstructions show that the distribution of tropical African rain forests was affected by Quaternary climate changes. They suggest that the Dahomey Gap (DG)—the savanna corridor that currently separates Upper Guinean (UG, West Africa) and Lower Guinean (LG, western Central Africa) rain forest blocks—was forested during the African Humid Holocene period (from at least 9 ka till 4.5 ka), and possibly during other interglacial periods, while an open vegetation developed in the DG under drier conditions, notably during glacial maxima. Nowadays, relics of semi-deciduous forests containing UG and LG forest species are still present within the DG. We used one of these species, the pioneer tree Terminalia superba (Combretaceae), to study past forest fragmentation in the DG and its impact on infraspecific biodiversity. A Bayesian clustering analysis of 299 individuals genotyped at 14 nuclear microsatellites revealed five parapatric genetic clusters (UG, DG, and three in LG) with low to moderate genetic differentiation (Fst from 0.02 to 0.24). Approximate Bayesian Computation analyses inferred a demographic bottleneck around the penultimate glacial period in all populations. They also supported an origin of the DG population by admixture of UG and LG populations around 54,000 (27,600–161,000) years bp, thus before the Last Glacial Maximum. These results contrast with those obtained on Distemonanthus benthamianus where the DG population seems to originate from the Humid Holocene period. We discuss these differences in light of the ecology of each species. Our results challenge the simplistic view linking population fragmentation/expansion with glacial/interglacial periods in African forest species.

Mammoths in Central America: New records from Guatemala

The remains of the Columbian Mammoth, Mammuthus columbi, are reported from four localities in Guatemala based on seven dental records. These localities are widely separated and include one specimen from Río La Pasión, Sayaxché, Departamento de Petén in the northern part of the country, one specimen from Chinautla, Departamento de Guatemala in the southwest and four specimens from the vicinity of Estanzuela, Departamento de Zacapa and one from Teculután, Departamento de Zacapa in the southeast. Based on the known records the distribution of Mammuthus in Central America tends to be concentrated on the Pacific side of the isthmus and suggests the former presence of a savanna corridor that formed during an interval of decreased precipitation.

Concordant genetic structure in two species of woodpecker distributed across the primary West African biogeographic barriers

The lowland forests of western and central tropical Africa are separated by several potential biogeographic barriers to dispersal for forest adapted vertebrates. The two primary barriers are (1) the Dahomey Gap, a savanna corridor that reaches the coast of southern Ghana, Togo and Benin, and separates the West African rainforest into the Upper (Ghana west to Guinea) and Lower Guinea (Nigeria to Uganda and Angola) forest blocks, and (2) the Lower Niger River, a large delta that separates Western and Eastern Nigeria. Previous studies on terrestrial vertebrates (lizards, mammals and birds) have highlighted a genetic break in the Dahomey Gap/Lower Niger River area although the relative importance of each barrier has not been assessed due to limitations in geographic sampling. We compared the phylogeographic history of two co-distributed sister-species of woodpeckers (Campethera caroli and C. nivosa) using data from three loci representing all inheritance modes. Our analyses revealed that both the Dahomey Gap and possibly the Lower Niger River acted as strong biogeographic barriers for the two woodpecker species, with the Lower Niger River being the first barrier to have formed, leading to three distinct populations of C. nivosa. Our divergence time analyses revealed that both these biogeographic barriers formed during the Pleistocene, supporting the Pleistocene refuge hypothesis, with the Dahomey Gap likely appearing about 0.5 myr BP. No genetic structure was recovered among sampled populations in either the Upper or the Lower Guinea Forest Block for both species, despite the considerable geographic area covered.

Barriers and bridges: early human dispersals in equatorial SE Asia

Abstract Past environments of equatorial SE Asia must have played a critical role in determining the timing and trajectory of early human dispersal into and through the region. However, very few reliable terrestrial records are available with which to contextualize human dispersal events. This circumstance, coupled with a sparse archaeological record and the likelihood that much of the archaeological record is now submerged, means we have an incomplete understanding of the role that geography, climate and environment played in shaping human pre-history in this region. From a review of the literature, we conclude that there must have been a substantial environmental barrier resulting in a genetic separation between east and west Sundaland that persisted even though a terrestrial connection was present for most of the Pleistocene. This barrier is likely to be a north–south corridor of open non-forest vegetation, and its existence may have encouraged the rapid dispersal of early humans through the interior of Sundaland and on to Sahul. We conclude that more reliable terrestrial palaeoenvironmental records are required to better understand the links between past environments and dispersal events. We highlight avenues of particular research value, such as focusing on eastern Sumatra, western/southern Borneo and the islands in the Java Sea, where the purported savanna corridor most probably existed, and including edaphic factors in palaeovegetation modelling.

Les primates quaternaires de Song Terus (Java Est, Indonésie) : implications paléobiogéographiques et archéozoologiques pour l’Asie du Sud-Est

Bones of non-human primates account for 70% of early Holocene mammal remains found in archaeological sites in the Punung region. Facial parts of monkeys have been found with pre-Neolithic human burials, as noted by van Heekeren. This thesis attempts to explain human/primate relationships froman analysis of the stratified remains of primates in the early Holocene layers in the caves of Song Terus, Gunung Sewu and East Java. Particular attention is given to the species Trachypithecus auratus, which accounts for 96% of the Song Terus primate bones. These are described morphologically and in relation to other genera and species of monkeys, including Macaca and Presbytis. Primate speciation patterns in the islands of South-East Asia suggest continuous connections between the Sunda Islands through forested terrain during the Pleistocene, making it unlikely that the region ever had a completely treeless savanna corridor during the glacial periods (which would have inhibited the movement of monkeys between islands). In parallel with a zooarchaeological approach, a study of tooth micro-wear suggests commensalism between certain monkeys and humans at Song Terus, especially in the period from 9000 to 5000 years ago.

Soils on exposed Sunda Shelf shaped biogeographic patterns in the equatorial forests of Southeast Asia

The marked biogeographic difference between western (Malay Peninsula and Sumatra) and eastern (Borneo) Sundaland is surprising given the long time that these areas have formed a single landmass. A dispersal barrier in the form of a dry savanna corridor during glacial maxima has been proposed to explain this disparity. However, the short duration of these dry savanna conditions make it an unlikely sole cause for the biogeographic pattern. An additional explanation might be related to the coarse sandy soils of central Sundaland. To test these two nonexclusive hypotheses, we performed a floristic cluster analysis based on 111 tree inventories from Peninsular Malaysia, Sumatra, and Borneo. We then identified the indicator genera for clusters that crossed the central Sundaland biogeographic boundary and those that did not cross and tested whether drought and coarse-soil tolerance of the indicator genera differed between them. We found 11 terminal floristic clusters, 10 occurring in Borneo, 5 in Sumatra, and 3 in Peninsular Malaysia. Indicator taxa of clusters that occurred across Sundaland had significantly higher coarse-soil tolerance than did those from clusters that occurred east or west of central Sundaland. For drought tolerance, no such pattern was detected. These results strongly suggest that exposed sandy sea-bed soils acted as a dispersal barrier in central Sundaland. However, we could not confirm the presence of a savanna corridor. This finding makes it clear that proposed biogeographic explanations for plant and animal distributions within Sundaland, including possible migration routes for early humans, need to be reevaluated.

Tropical and western influences in vertebrate faunas from the Pliocene and Pleistocene of Florida

Extralimital and extinct species of birds and mammals with either tropical or western affinities are characteristic of numerous Florida Pliocene and Pleistocene vertebrate faunas. These sites document nonanalog or disharmonious faunas, recording the association of certain genera or species that are no longer sympatric, in particular taxa now restricted to drier habitats in western North America or tropical habitats in Middle America occurring together with species still found in Florida and the southeastern United States. Extralimital or extinct taxa of western origin in Florida Plio-Pleistocene nonanalog faunas include: the mammals Antrozous, Lepus, Spermophilus, Thomomys, and Baiomys; and the birds Gymnogyps californianus, Teratornis merriami, Aquila chrysaetos, Tympanuchus cupido, two species of Glaucidium, and Pica pica. A large influx of tropical species occurred in Florida late Blancan and early Irvingtonian sites, primarily consisting of taxa of South American origin involved in the Great American Biotic Interchange. Besides large Interchange mammals, other mammals with tropical affinities now extinct or extralimital to Florida include: the bats Desmodus archaeodaptes, Desmodus stocki, Mormoops megalophylla, Pteronotus pristinus, and Eumops underwoodi, the carnivores Leopardus pardalis, Leopardus wiedii, Panthera onca, two species of Conepatus, and Tremarctos floridanus, and the peccary Pecari. Tropical birds in Florida Plio-Pleistocene faunas include the extralimital Tachybaptus dominicus, Laterallus exilis, Jacana spinosa, Buteogallus urubitinga, Milvago chimachima, Vanellus chilensis, and Ceryle torquata; as well as several extinct species including Titanis walleri, a chachalaca (Family Cracidae), Amplibuteo concordatus, Spizaetus grinnelli, and Cremaster tytthus. These tropical and western taxa indicate the presence of biogeographic corridors during Plio-Pleistocene glacial intervals that connected the Florida peninsula to both the arid western United States and tropical Middle America. A mosaic of desert grassland and savanna habitats intermixed with wetlands apparently extended eastward from the arid Southwest through Texas and along a southeastern corridor to the Florida peninsula. A Gulf Coast savanna corridor supporting savanna and thorn scrub habitats probably existed during glacial low sea level stands on the exposed continental shelf and coastal plain along the northern margin of the Gulf of Mexico, connecting the Florida peninsula with Mexico and Central America. The occurrence of both tropical and western taxa in some of the same faunas strongly indicates that these distributional patterns were contemporaneous and corresponded to climatic conditions and vegetational associations that no longer exist in Florida.

Palaeoenvironments of insular Southeast Asia during the Last Glacial Period: a savanna corridor in Sundaland?

Consideration of a range of evidence from geomorphology, palynology, biogeography and vegetation/climate modelling suggests that a north-south ‘savanna corridor’ did exist through the continent of Sundaland (modern insular Indonesia and Malaysia) through the Last Glacial Period (LGP) at times of lowered sea-level, as originally proposed by Heaney [1991. Climatic Change 19, 53–61]. A minimal interpretation of the size of this corridor requires a narrow but continuous zone of open ‘savanna’ vegetation 50–150 km wide, running along the sand-covered divide between the modern South China and Java Seas. This area formed a land bridge between the Malaysian Peninsula and the major islands of Sumatra, Java and Borneo. The savanna corridor connected similar open vegetation types north and south of the equator, and served as a barrier to the dispersal of rainforest-dependent species between Sumatra and Borneo. A maximal interpretation of the available evidence is compatible with the existence of a broad savanna corridor, with forest restricted to refugia primarily in Sumatra, Borneo and the continental shelf beneath the modern South China Sea. This savanna corridor may have provided a convenient route for the rapid early dispersal of modern humans through the region and on into Australasia.

The Dahomey Gap: an abrupt climatically induced rain forest fragmentation in West Africa during the late Holocene

The Dahomey Gap, a savanna corridor interrupting the zonal West African rain forest, did not exist during the mid-Holocene. The pollen diagram from Lac Sélé (7°9'N, 2°26'E) indicates that in southern Benin a semi-evergreen rainforest prevailed between c. 8400 and 4500 cal. yr BP. The mid-Holocene marine transgression caused a spread of mangrove forest along the inland lagoons. Pollen analysis and geochemistry indicate that the Dahomey Gap became established at the onset of the late Holocene due to an abrupt climatic change between c. 4500 and 3400 cal. yr BP. Drier climatic conditions led to a rapid deterioration of the rain forest and subsequent spread of Sudano-Guinean savannas. A return to wetter climatic conditions between c. 3300 and 1100 cal. yr BP resulted in a rise in the lake level and a renewed spread of forests into the savanna. During this time the Dahomey Gap consisted of a forest-savanna mosaic with a high number of pioneer tree taxa including the oil palm Elaeis guineensis After c. 1100 cal. yr BP the lake level dropped again and the Lac Sélé profile indicates drier environmental conditions resulting in the establishment of an open savanna which persists until present. The palaeorecord from Lac Sélé suggests that the role of humans in shaping the West African savannas has been overestimated. The opening of the Dahomey Gap and spread of the oil palm E. guineensis can now be confidentially attributed to climatic change and was not initiated by humans.

Vegetation change in equatorial West Africa: time-slices for the last 150 ka

Drawing on marine and terrestrial palynological data, vegetation maps of equatorial West Africa are presented for eleven time slices over the last 150,000 years. Long marine records are used as a basis for the regional picture and provide a chronology for the last glacial cycle. Much shorter terrestrial records help fill in the picture for the most recent periods and facilitate interpretation of regional patterns for the longer timescale. Temporal and spatial variation is revealed in relation to global patterns of climate change. Rain forest was widespread during Oxygen Isotope Stages 1 and 5, but strongly reduced during Stages 3 and 4 and especially during Stages 2 and 6 when open, grass-rich vegetation prevailed. Glacial rain forest refuges are found in the southwest of the Guinean mountains and along the eastern coast of the Gulf of Guinea. Miombo woodland of the Zambezian vegetation zone expanded during Stage 5, especially during the first half. Podocarpus forest had its largest expansion during Substages 5d (115 to 105 ka) and 5b (95 to 85 ka). The last occurrence of Podocarpus in the Guinean mountains is during Stage 5a. The distribution of mangrove swamps was extremely reduced during glacial times. During Stage 6, savanna and open dry forest covered large areas along the northern coast of the Gulf of Guinea. The southern Saharan desert reached far to the south and the Namib desert far to the north. The area of rain forest was restricted, mangrove swamps were strongly reduced, and the area of Podocarpus forest fluctuated. During Stage 5 large changes in the area of Afromontane forest, rain forest, dry open forest and savanna occurred. Rain forest was widespread and mangroves were extensive along the coast during the last interglacial (Substage 5e). Podocarpus forest area strongly extended during Substages 5d and 5b. In Substages 5c and 5a, rain forest reclaimed areas it had lost in the previous substages (5d and 5b, respectively). Mangrove swamps were less widespread in the later substages of Stage 5 than during Substage 5e. During Stage 4, the rain forest area was again strongly reduced, and recovered only slightly during the following Stage 3. Also the mangrove swamp area was reduced except along the Ivory Coast and along the northwestern coast of the Gulf of Guinea. Podocarpus forest only occurred in Angola and may be in Congo during Stage 4. Again forest was much reduced during Stage 2 and open vegetation types covered large parts of equatorial West Africa. Mangrove swamps must have been rare. At the beginning of the Holocene, mangrove swamps had recovered and reached their largest extension. Also the rain forests area increased in the early Holocene and Guinean and Congolian rain forests were probably not separated by a savanna corridor now existing in Togo and Benin.

Vegetation history of the savanna corridor between the Guinean and the Congolian rain forest during the last 150,000 years

Pollen and spores from a deep-sea core located west of the Niger Delta record an uninterrupted area of lowland rain forest in West Africa from Guinea to Cameroon during the last Interglacial and the early Holocene. During other periods of the last 150 ka, a savanna corridor between the western — Guinean — and the eastern — Congolian — part of the African lowland rain forest existed. This so-called Dahomey Gap had its largest extension during Glacial Stages 6, 4, 3, and 2. Reduced surface salinity in the eastern Gulf of Guinea as recorded by dinoflagellate cysts indicates sufficient precipitation for extensive forest growth during Stages 5 and 1. The large modern extension of dry forest and savanna in West Africa cannot be solely explained by climatic factors. Mangrove expansion in and west of the Niger Delta was largest during the phases of sea-level rise of Stages 5 and 1. During Stages 6, 4, 3, and 2, shelf areas were exposed and the area of the mangrove swamps was minimal.

First Record of Giant Anteater (Xenarthra, Myrmecophagidae) in North America

A right metacarpal III represents the first North American record of the giant anteater (Myrmecophaga tridactyla). Recovered in northwestern Sonora, Mexico, with a rich vertebrate fauna of early Pleistocene (Irvingtonian) age, it belongs to a cohort of large mammals that dispersed from South America to North America along a savanna corridor. Presumably habitat and climatic changes have subsequently driven this mammalian family more than 3000 kilometers back into Central America from its former expansion into temperate North America.