The minimum age (250 Ma) was taken from the youngest possible age of the fossil and the upper boundary was set equal to the next-oldest calibrated node (Bilateria).
As our understanding of eukaryote phylogeny improved, fossil-calibrated molecular clock-based methods were beginning to be applied to date the major diversification events in this domain (Hedges et al. 2004; Hedges and Kumar 2004; Berney and Pawlowski 2006; Parfrey et al. Molecular clock analyses were first introduced by Zuckerkandl and Pauling (1965).
It was later shown that these sterol biomarkers were younger than the rocks in which they were found (Fischer 2008; Rasmussen et al.We show that for major eukaryote groups estimated dates of divergence, as well as their credible intervals, are heavily influenced by the relaxed molecular clock models and methods used, and by the nature and treatment of fossil calibrations. Maximum likelihood phylogenetic tree of eukaryotes based on a phylogenomic dataset.Whereas the estimated age of LECA varied widely, ranging from 1007 (943–1102) Ma to 1898 (1655–2094) Ma, all analyses suggested that the eukaryotic supergroups subsequently diverged rapidly (i.e., within 300 Ma of LECA). Additional taxa were added to the original 159-gene Brown et al.2008), although there have been new strictly controlled studies reporting steranes in similar aged sediments (Waldbauer et al. A bacterial origin of these biomarkers cannot be excluded as some bacteria make sterols.However, these differ from many that are characteristic of specific eukaryotes (Summons et al. In general, biomarkers need to be considered carefully as contamination is difficult to rule out, and their specificity to one lineage cannot be guaranteed, especially for microbes in which lateral gene transfer is prevalent. Many microfossils of suggested eukaryotic origin are large (50 μm) organic-walled structures known as acritarchs (Buick and Young 2010; Javaux et al. The oldest of these are microfossils described from the ∼3.2-billion-year-old (Ga) Moodies group (Buick and Young 2010; Javaux et al.