The scientific core content of the ToL project is presented on leaf and branch pages. Leaf pages represent the tips of the tree of life, while branch pages represent groups containing several related subgroups. The Root Page of the ToL is a special kind of branch page, providing information on the characteristics of all Life on Earth and the relationships among the major lineages of organisms.
Articles, notes, and treehouses are attached to leaf and branch pages, which provide the structural backbone for the ToL project.
In addition to the scientific core content presented on branch and leaf pages, the ToL project features other scientific articles, notes, and treehouses, which are attached to one or more leaves or branches of the tree of life.
In order to put the information about individual groups in a phylogenetic context, ToL branch pages feature a tree diagram (or a list of subgroups if relationships among subgroups are unknown). Tree diagrams provide an overview of the phylogenetic relationships among subgroups. For example, the tree diagram of the beetle page (Coleoptera) looks like this:
The tree diagram on the beetle (Coleoptera) page showing the relationships between the major beetle subgroups.
The basal branching point in the Coleoptera tree represents the ancestor of all beetles. This ancestor diversified over time into several descendent subgroups, which are represented as internal nodes (branching points) and terminal taxa at the tips of the beetle tree. Beginning at the root on the left, the diagram shows that the ancestral beetle lineage gave rise, on the one hand, to members of the extinct Paleozoic group Protocoleoptera, and on the other to the ancestor of the remaining beetles. This ancestor in turn split into a species that gave rise to the extinct family Permocupedidae, and another that gave rise to the remainder of the beetles. Further splitting of ancestral species would lead us to the terminal taxa in the diagram, where we see Polyphaga and Myxophaga on adjacent branches. The ancestral species of these two groups split in two to give rise to one species that was the ancestor of the Polyphaga, and another species that was the ancestor of the Myxophaga. Even though it isn't shown on this diagram, the splits implied in this tree probably happened in the Permian period, before the time of the dinosaurs.
Please refer to Interpreting the Tree Diagram or Taxon List on a Tree of Life Page for more information about ToL tree diagrams.
Terminal taxon names that are underlined and printed in blue represent links to ToL pages about a particular subgroup. By clicking on the names of these groups, ToL visitors can thus move up to a branch higher in the tree of life. For example, in the beetle tree, one can move up to the branch pages of the beetle subgroups Polyphaga, Myxophaga, Adephaga, and Archostemata. On each of these pages, there will then be another tree diagram with links to subgroups leading further up the branches of the tree of life. In this way, one can move from Coleoptera to Adephaga to Carabidae and then to Gehringia olympica, which is a beetle species, representing a leaf on the tree of life.
Terminal taxon links in ToL tree diagrams let visitors move up the branches of the tree of life, all the way to leaf pages.
The root of the beetle tree ()
connects the beetles to their containing group, the Endopterygota (insects
with complete metamorphosis). ToL visitors can click on this root to move
down the tree of life to the Endopterygota page. On the Endopterygota
page, there's a tree diagram showing the relationships between the Endopterygota
subgroups, including the beetles (Coleoptera). Clicking on the root of
the Endopterygota tree will take visitors further down to the Neoptera
page, and clicking on the root of the Neoptera tree will lead down one
step further to the Pterygota page. If one were to keep on clicking on
the roots of ToL branch pages, one would eventually get to the root page
for the entire project representing Life on Earth, the ultimate containing
group for all organisms.
Root links in ToL tree diagrams let visitors travel down the branches of the tree of life to ever more inclusive containing groups.
Links between ToL pages let visitors explore the evolutionary tree of life from the bottom up or from the top down.
The tree diagram or taxon list on each ToL branch page is linked to the trees/lists of the pages for related groups. All ToL pages taken together therefore present current ideas about the structure of the entire evolutionary tree of living things (at least to the extent that the project has been developed so far). Following the links up and down the tree, you can wander along the branches, exploring the diversity of many different kinds of organisms, while at the same time being reminded of the genetic connectedness of all of Life.
You may begin you journey at the root of all Life on Earth, travelling up the tree through levels of ever less inclusive groups, all the way up to the leaf pages of individual species or subspecies. Or you may start your exploration on a leaf page, following the link to its containing group and then moving through ever more inclusive containing groups, all the way down to the root.
In addition to the tree diagram or taxon list, ToL pages feature links to other organisms in the Explore Other Groups menu in the right sidebar. For more information about all the different navigation options, please refer to the Navigating the ToL page.