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. The following tree 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. The following tree 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
The above tree illustrates the time of first appearance of each stem group (where known) and their phylogenetic relationships, or lines of descent from ancestors to descendants.
A striking aspect of the above tree is the great variation in the time interval between the appearance of the oldest known stem group fossil and the formation of two new clades at the next crown node.
Another way of representing this variation is to plot the number of new clades (represented by stem group fossils) appearing in successive intervals of geological time, as shown below:
A striking aspect of the above tree is the great variation in the time interval between the appearance of the oldest known stem group fossil and the formation of two new clades at the next crown node.
Another way of representing this variation is to plot the number of new clades (represented by stem group fossils) appearing in successive intervals of geological time, as shown below:
Figure 3. Appearance of basal crown vertebrate clades over geological time
This plot indicates that the appearance of new clades was fastest over the interval from around 430 to 410 million years (mid-Silurian to early Devonian). This implies that these five clades – Osteichthyes, Sarcopterygii, Coelacanthi, Dipnoi and Actinopterygii - all appeared within an interval of about 12 million years, corresponding to a new clade roughly every 2.5 million years on average. This is fast compared to the rates (15 to 19 million years per clade, on average) seen elsewhere in Figure 3.
Reference
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.