The vertebrates (subphylum Vertebrata, Phylum Chordata) are characterized by having a vertebral column. They are also characterized by a muscular system consisting primarily of bilaterally paired masses and a central nervous system partly enclosed within the backbone (Encyclopaedia Britannica).
A summary of the phylogeny of the vertebrate clade is shown below:
A summary of the phylogeny of the vertebrate clade is shown below:
Figure 1. Summarized phylogenetic tree of the vertebrates
Each page of this website deals with a single branch of the phylogenetic tree and presents the fossils that have been interpreted to belong to the corresponding stem group. Links to the pages corresponding to the branches shown above (except for those for which no stem-group fossils are known) can be found under the Navigation tab above.
The following pages present phylogenetic trees that illustrate the history of development of each stem group. If we summarize and combine these data, we can construct a phylogenetic time tree for the entire vertebrate tree up to the tetrapods. All of the time trees presented in this website were created using the R packages "strap" (Bell and Lloyd, 2015) or "paleotree" (Bapst, 2012). The following tree, constructed using a minimum branch length of 2 million years in the paleotree package, illustrates how the successive stem groups relate to one another through geological time. For simplicity, each stem group is represented by the oldest known member of that stem group:
The following pages present phylogenetic trees that illustrate the history of development of each stem group. If we summarize and combine these data, we can construct a phylogenetic time tree for the entire vertebrate tree up to the tetrapods. All of the time trees presented in this website were created using the R packages "strap" (Bell and Lloyd, 2015) or "paleotree" (Bapst, 2012). The following tree, constructed using a minimum branch length of 2 million years in the paleotree package, illustrates how the successive stem groups relate to one another through geological time. For simplicity, each stem group is represented by the oldest known member of that stem group:
Figure 2. Summarized phylogenetic time tree of the vertebrates
An interesting observation that we can make from the above tree is that the crown group of the Actinopterygii (the ray-finned fishes) continued evolving long after the appearance of the stem group of the tetrapods.
Reference
Bapst, D. W. (2012). paleotree: an R package for paleontological and phylogenetic analyses of evolution. Methods in Ecology and Evolution, 3(5), 803-807.
Bell, M. A., & Lloyd, G. T. (2015). strap: an R package for plotting phylogenies against stratigraphy and assessing their stratigraphic congruence. Palaeontology, Vol. 58, No. 2, pp. 379-389.
Bell, M. A., & Lloyd, G. T. (2015). strap: an R package for plotting phylogenies against stratigraphy and assessing their stratigraphic congruence. Palaeontology, Vol. 58, No. 2, pp. 379-389.