Cretaceous origin of tropical rainforest in Africa and the Levant and the implications for modern climate predictions

点击翻译按钮获取中文摘要

Modern tropical rain forests (TRF) are one of the most important and species rich biomes on the planet. Rainforest environments have an enormous impact on the global water and heat circulation and play therefore a major role in the water distribution and the rainfall patterns . Fossil TRF, characterized by their physiognomy (e.g. broad entire-margined leaves with drip tips), climate proxies and high diversity, usually about 25 sp. in a single quarry (as well as in a single modern TRF leaf litter sample) and more than 100 sp. in a regional assemblage, have not been identified so far before the latest Cretaceous (ca 72 Myr ago). Nevertheless, fossil calibrated phylogenies of TRF clades point to a much older origin of this biome, at the beginning of the late Cretaceous (100 Myr ago).Our study of late Cretaceous North Gondwanan floras will be based on material from Egypt, Sudan and Israel, which as noted above are key to understanding the origin of modern TRF. Rich collections from these areas, originally from the TU Berlin but now in the collections of the MfN. In spite of the published description of some floras, most of the material is unpublished. In addition to this material, the National Natural History Collections of the Hebrew University of Jerusalem house two collections and new material has benn recently collected from Egypt.Several clues make us confident that we will discover true rainforests. Among the fossil leaves, a rich assemblage of monocots is currently described and include Araceae closely related to modern taro and philodendron plants, living in tropical rainforests. Secondly the paleoprecipitation reconstructed for floras from Egypt and Sudan indicate an increase between the uppermost Lower Cretaceous (Mean Annual Precipitation ca 1500mm) and the latest Cretaceous (Mean Annual Precipitation ca 2000mm) with at least one drought episode (ca 800 mm). Furthermore, the overall physiognomy, mean size, shape and consistency of the leaves of some of the floras resembles modern rainforests. In order to understand the origin of the TRF vegetation which is so crucial to our world climate, we have to study new material from an area where rainforest might have had its origin, namely North Gondwana. Climate conditions at this time have to be worked out much more thoroughly, especially with the aim to understand in which climate regime this tropical rainforest biome can exist. The reconstruction of this scenario might help to predict the disappearance of tropical rainforest due to future climate change when low latitudes might suffer the loss of this biome.