The evolution of life is a vast topic, involving an immense literature representing biological and geological disciplines. Only a relatively small fraction of this field of knowledge can be covered here: the extent to which the process of evolution is documented by means of fossils. There are many life-forms that are not known as fossils, such that their evolution cannot be observed by paleontology. This study therefore deals only with organisms that have been found in fossil form.
The following phylogenetic tree shows the classification of organisms that are known as fossils:
The following phylogenetic tree shows the classification of organisms that are known as fossils:
The black dots represent the nodes of the successive crown groups into which life has divided. All of the groups on the right-hand side of this tree have fossil representatives. However, many of them are not sufficiently well represented to provide useful information on their evolution, so this website will deal only with the two groups that have an excellent fossil record, the animals (otherwise known as the Metazoa) and the land plants.
The animals belong to several higher groups:
The land plants are also eucaryotes, but they also belong to these groups:
The remainder of this main section of the website is thus divided into two parts, dealing with the evolution of the animals and the land plants respectively.
The animals belong to several higher groups:
- Opisthokonts: the combined clade of fungi and animals, illustrating their common ancestor
- Podiates: the combined clade of opisthokonts and amoeba, thought to have evolved through the development of ventral pseudopodia (Cavalier-Smith et al, 2014)
- Eucaryotes: all organisms that have cells in which the nucleus is enclosed within a membrane.
The land plants are also eucaryotes, but they also belong to these groups:
- Corticates: eucaryotes having a cortex (bark, husk or rind)
- Plantae: corticates that photosynthesize.
The remainder of this main section of the website is thus divided into two parts, dealing with the evolution of the animals and the land plants respectively.
Photo credit
Header: Stromatolite, Quebec, Canada. By André-P. Drapeau P. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], from Wikimedia Commons
Header: Stromatolite, Quebec, Canada. By André-P. Drapeau P. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], from Wikimedia Commons