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20151050Time: million years before presentLandscape, climate and human evolutionLandscapeEvolutionEast African rift flank upliftVolcanism

riftingLake formationClimateEvolution

Rain forestwoodlandgrasslandHomininEvolutionThe African climate inferred from pollen and molecular recordEast African climate evolution

Pollen

20806040Grasses (Poaceae) %40200Desert & sem-desert (%)

-22-24-26-28-30

3456798Million years agoRainforest grassland(wet) (relative dry)Rainforest grassland(wet) (relative dry)

Pollen and molecular records extracted from lake/marine sediment indicate that an expansion of grassland at expense of rainforest areasC3 photosynthetic pathway:

Mesophyll cellBundle-sheath cellSpatial separation of stepsglucoseCO2CO2CalvinCycleOrganic acidTemporal separation of stepsCrassulacean acid metabolism:(CAM photosynthesis)

glucoseCO2CO2CalvinCycleOrganic acidNight

DayThe African climate inferred molecular recordsEast African climate evolutionThe photosynthetic pathways of C4 and CAM plants reduce the loss of water. For example: When grown in the same environment, at 30C, C3 grasses lose approximately 833 molecules of water per CO2 molecule that is fixed, whereas C4 grasses lose only 277 water molecules. Therefore C4 plans CAM are more competitive in semi- arid and arid area. Because the photosynthesis in C4 and CAM plants occurs in closed/separated system, the ability of plants to preferential incorporate 12CO2 is limited resulting in relative high 13C/12C in the plants compounds The emergence and expansion of aridity-adapted plants around 5-7 million yearsMesophyll cellglucoseCO2CalvinCycleEnzymaticreactionC4 photosynthetic pathway:

Changes in vegetation in East African Rift Valley

Million years BPAwash Valley

01234Fraction of wood cover (areal basisVegetation changesThe African climate inferred from animal habitatEast African climate evolutionEast African climate evolution

The African climate inferred from animal habitatEast African climate evolution

East African climate evolution40 %30 %20 %10 %0 %50%GrasslandWetwoodlandShrublandWoodlandBushlandEcotoneForestVariation in the ratio of adaptations (food types and habitats) in modern mammal communities for different ecosystems in Africa. grazingFruit-eatingTree-livingFood types and habitats of mammal: indicator of vegetation and climateThe African climate inferred from animal remainsEast African climate evolutionEvolution of African Megafauna

34-2838-3428-2423-1616-11.611.6-5.35.3-2.62.6-1.81.8-0.80.8-0.017presentMillion years agoThe African climate inferred from animal remainsEast African climate evolution

Bovidae are all mammals that are cloven-hoofed and ruminant with characteristic unbranching horns (at least the males)Suidae the biological family to which pigs belongs

Cercopithecoidea (Old World monkeys) are monkeys native to Africa and Asia today, inhabiting a range of environments from tropical rains forest to savanna, shrubland and mountainous terrainEvolution and shift in the composition of East African mammals

The African climate inferred from animal remainsEast African climate evolution

Hippotragini

Antilopini

AlcelaphiniGrasser as % of Bovidae*

Bovidae are all mammals that are cloven-hoofed, ruminant mammals with characteristic unbranching horns (at least the males)The graph shows en increase of animals that are adapted to grassland.

Climate proxies: dustsEast African climate evolution

West AfricaAtlantic Ocean

AfricaThe Dust: Indicator of Climate changesEast African climate evolutionMore dustLessdustMillion years ago

In crease of African dust in marine sedimentsThe Climate Archives: Lake sedimentsEast African climate evolution

Fluctuation of East African lakesSummery:

In response to global and regional long-termclimate changes, East Africa experienced more or less continuous aridification starting from5.5 million years ago.

This climate change led to fundamental shifts In the vegetation and mammal comminitiesEast African climate evolution13