摘要
Examples of evolution,extinction and homoplasy of the larger benthic foraminifera(LBF)occur throughout their history.Since the Carboniferous,LBF have thrived in carbonate-rich tropical and subtropical shallow-marine shelf environments.Their high abundance and diversity are due primarily to their extraordinary ability to inhabit a range of ecological niches and by hosting a variety of symbionts.Attaining relatively large,centimetre-scale sizes,made some forms very specialized and vulnerable to rapid ecological changes.For this reason,some LBF have shown a tendency to suffer periodically during major extinctions,especially when environmental conditions have changed rapidly and/or substantially.This,however,makes them valuable biostratigraphic microfossils and,in addition,gives invaluable insight into the spatial and temporal process of biological evolution,such as convergent/homoplasy and homology/iterative evolution.Here the evolutionary behavior of two important morphological types that occurred throughout the history of the LBF are discussed,namely the planispiral-fusiform test as typified by the fusulinids in the Late Paleozoic and the alveolinids in the Mid-Cretaceous and Neogene,and the three-layered discoid lenticular test as characterized by the orbitoids in the Mid-to Late Cretaceous,the orthophragminids in the Paleogene,and lepidocyclinids in the Oligocene to Quaternary.Understanding the propensity of these forms to convergent and iterative evolution,with the repeated re-occurrence of certain morphological features,is essential in understanding and constructing their phylogenetic relationships more generally within the main groups of the LBF.The insights gained from the history of these LBF have wider implications,and provide a more general understanding of the impacts of climate and ecological changes as driving forces for biological evolution.
