Jacobs Bonnie F
Environmental Science Program, Southern Methodist University, PO Box 750395, Dallas, TX 75275-0395, USA.
Philos Trans R Soc Lond B Biol Sci. 2004 Oct 29;359(1450):1573-83. doi: 10.1098/rstb.2004.1533.
Fossil plants provide data on climate, community composition and structure, all of which are relevant to the definition and recognition of biomes. Macrofossils reflect local vegetation, whereas pollen assemblages sample a larger area. The earliest solid evidence for angiosperm tropical rainforest in Africa is based primarily on Late Eocene to Late Oligocene (ca. 39-26 Myr ago) pollen assemblages from Cameroon, which are rich in forest families. Plant macrofossil assemblages from elsewhere in interior Africa for this time interval are rare, but new work at Chilga in the northwestern Ethiopian Highlands documents forest communities at 28 Myr ago. Initial results indicate botanical affinities with lowland West African forest. The earliest known woodland community in tropical Africa is dated at 46 Myr ago in northern Tanzania, as documented by leaves and fruits from lake deposits. The community around the lake was dominated by caesalpinioid legumes, but included Acacia, for which this, to my knowledge, is the earliest record. This community is structurally similar to modern miombo, although it is different at the generic level. The grass-dominated savannah biome began to expand in the Middle Miocene (16 Myr ago), and became widespread in the Late Miocene (ca. 8 Myr ago), as documented by pollen and carbon isotopes from both West and East Africa.
化石植物提供了有关气候、群落组成和结构的数据，所有这些都与生物群落的定义和识别相关。大化石反映了当地植被，而花粉组合则对更大区域进行了采样。非洲被子植物热带雨林的最早确凿证据主要基于喀麦隆晚始新世至晚渐新世（约3900万至2600万年前）的花粉组合，这些组合富含森林科属。非洲内陆其他地区这一时期的植物大化石组合很少见，但埃塞俄比亚高地西北部奇尔加的新研究记录了2800万年前的森林群落。初步结果表明其植物学亲缘关系与西非低地森林有关。热带非洲已知最早的林地群落可追溯到4600万年前的坦桑尼亚北部，湖泊沉积物中的树叶和果实证明了这一点。湖边的群落以苏木亚科豆科植物为主，但也包括金合欢属植物，据我所知，这是该属植物最早的记录。这个群落结构上与现代的稀树草原相似，尽管在属级水平上有所不同。以草为主的稀树草原生物群落在中新世中期（1600万年前）开始扩张，并在中新世晚期（约800万年前）广泛分布，西非和东非的花粉和碳同位素都证明了这一点。
