ABSTRACT
The colonization of land by eukaryotes probably was facilitated by a partnership (symbiosis) between a photosynthesizing organism (phototroph) and a fungus. However, the time when colonization occurred remains speculative. The first fossil land plants and fungi appeared 480 to 460 million years ago (Ma), whereas molecular clock estimates suggest an earlier colonization of land, about 600 Ma. Our protein sequence analyses indicate that green algae and major lineages of fungi were present 1000 Ma and that land plants appeared by 700 Ma, possibly affecting Earth's atmosphere, climate, and evolution of animals in the Precambrian.
Subject(s)
Biological Evolution , Chlorophyta , Fungal Proteins/chemistry , Fungi , Chlorophyta/genetics , Chlorophyta/growth & development , Databases, Factual , Ecosystem , Fossils , Fungal Proteins/genetics , Fungi/chemistry , Fungi/genetics , Fungi/growth & development , Phylogeny , Plants/genetics , Rhodophyta/genetics , Rhodophyta/growth & development , Sequence Alignment , Sequence Analysis, Protein , Symbiosis , TimeABSTRACT
Although the relationships of the living hominoid primates (humans and apes) are well known, the relationships of the fossil species, times of divergence of both living and fossil species, and the biogeographic history of hominoids are not well established. Divergence times of living species, estimated from molecular clocks, have the potential to constrain hypotheses of the relationships of fossil species. In this study, new DNA sequences from nine protein-coding nuclear genes in great apes are added to existing datasets to increase the precision of molecular time estimates bearing on the evolutionary history of apes and humans. The divergence of Old World monkeys and hominoids at the Oligocene-Miocene boundary (approximately 23 million years ago) provides the best primate calibration point and yields a time and 95% confidence interval of 5.4 +/- 1.1 million years ago (36 nuclear genes) for the human-chimpanzee divergence. Older splitting events are estimated as 6.4 +/- 1.5 million years ago (gorilla, 31 genes), 11.3 +/- 1.3 million years ago (orangutan, 33 genes), and 14.9 +/- 2.0 million years ago (gibbon, 27 genes). Based on these molecular constraints, we find that several proposed phylogenies of fossil hominoid taxa are unlikely to be correct.
