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 can only be determined using molecular (DNA) analysis rather than by paleontology. This study deals only with organisms that have been found in fossil form. However, many of the phylogenetic trees presented in this website are based at least partly on molecular data.
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 sufficient information to illustrate their evolution, so this website will deal only with the two groups that have an excellent fossil record, the animals (or Metazoa) and the land plants (or Embryophyta).
All of the groups shown on the right-hand side of the above tree, except for the cyanobacteria, belong to the Eukaryotes, which comprise all organisms that have cells in which the nucleus is enclosed within a membrane (Biology Online Dictionary). The cyanobacteria, also known as “blue-green algae”, belong to the Prokaryotes, which are organisms whose cells do not contain a distinct nucleus bounded by a nuclear envelope (Biology Online Dictionary).
The remainder of this main section of the website is divided into five parts:
• The origin of the eukaryotes
• Evolution of the animals
• Evolution of the land plants
• References
• Glossary of terms
All of the groups shown on the right-hand side of the above tree, except for the cyanobacteria, belong to the Eukaryotes, which comprise all organisms that have cells in which the nucleus is enclosed within a membrane (Biology Online Dictionary). The cyanobacteria, also known as “blue-green algae”, belong to the Prokaryotes, which are organisms whose cells do not contain a distinct nucleus bounded by a nuclear envelope (Biology Online Dictionary).
The remainder of this main section of the website is divided into five parts:
• The origin of the eukaryotes
• Evolution of the animals
• Evolution of the land plants
• References
• Glossary of terms
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