The purpose of this page is to illustrate the phylogeny of the bird crown group and discuss the paucity of stem-group fossils for clades within the crown group.
The following phylogenetic tree is taken from a recent article that points out that phylogenetic relationships within the bird crown group remain controversial, despite great efforts in research over recent decades (Stiller et al, 2024):
The following phylogenetic tree is taken from a recent article that points out that phylogenetic relationships within the bird crown group remain controversial, despite great efforts in research over recent decades (Stiller et al, 2024):
Figure 1. Phylogenetic tree of the crown-Aves
This tree should be considered as one possible topology among several others that have been published but will not be considered here, in the interests of brevity.
As many of the clade names shown above might not be familiar to some readers, the bird groups included in each clade are listed below:
As many of the clade names shown above might not be familiar to some readers, the bird groups included in each clade are listed below:
Clade |
Bird group |
Australaves |
Falcons; parrots; seriemas; songbirds. |
Afroaves |
Hawks and relatives; hornbills and relatives; kingfishers and relatives; mousebirds; owls; trogons; woodpeckers and relatives; the cuckoo roller. |
Elementaves |
Albatrosses and relatives; cormorants and relatives; loons (divers); pelicans and relatives; penguins; storks; kagus; tropicbirds; nightjars, swifts and hummingbirds; shorebirds; cranes and relatives; the hoatzin. |
Columbaves |
Bustards; cuckoos; mesites; pigeons and doves; sandgrouse; turacos. |
Mirandornithes |
Flamingos and grebes. |
Notopalaeognathae |
Cassowaries and emus; kiwis; rheas; tinamous. |
The phylogenetic time tree shown below was created, using the "DatePhylo" routine of the R package "strap"; Bell and Lloyd (2015), from the topology of Figure 1 and the ages of fossils representing the crown group:
Figure 2. Time tree of the crown-Aves (root age 97.9 million years)
A striking aspect of the above tree is the general lack of stem group fossils, especially for the intermediate nodes. Some stem group fossils are known for the terminal clades, but in most cases the age is constrained by the crown group or, for the order Anseriformes, by an undifferentiated total group. There is no consensus in the literature on fossils that might represent the stem groups of the Neognathae, Palaeognathae, Neoaves or Gallanserae.
The oldest known fossil assigned to a clade within the crown-Aves is the total-group anseriform Conflicto antarcticus, described from the López de Bertodano Formation of Danian age on Seymour Island, Antarctica (Tambussi et al, 2019):
The oldest known fossil assigned to a clade within the crown-Aves is the total-group anseriform Conflicto antarcticus, described from the López de Bertodano Formation of Danian age on Seymour Island, Antarctica (Tambussi et al, 2019):
Figure 3. Skeletal reconstruction of Conflicto antarcticus
However, Conflicto antarcticus is not the oldest member of the bird crown group. That distinction belongs to Asteriornis maastrichtensis, of Late Maastrichtian age, as discussed on the previous page. The age of this fossil is shown as a red bar in Figure 2 above.
Very few images are available in the public domain for stem-group fossils in the crown group. None will be reproduced here because they do not shed significant light on the evolution of the crown-Aves. However, information about these fossils can be found in the Excel file in the Data section of the website.
Very few images are available in the public domain for stem-group fossils in the crown group. None will be reproduced here because they do not shed significant light on the evolution of the crown-Aves. However, information about these fossils can be found in the Excel file in the Data section of the website.
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References
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.
Stiller, J., Feng, S., Chowdhury, A. A., Rivas-González, I., Duchêne, D. A., Fang, Q., ... & Zhang, G. (2024). Complexity of avian evolution revealed by family-level genomes. Nature, 629(8013), 851-860.
Tambussi, C. P., Degrange, F. J., De Mendoza, R. S., Sferco, E., & Santillana, S. (2019). A stem anseriform from the early Palaeocene of Antarctica provides new key evidence in the early evolution of waterfowl. Zoological Journal of the Linnean Society, 186(3), 673-700.
Stiller, J., Feng, S., Chowdhury, A. A., Rivas-González, I., Duchêne, D. A., Fang, Q., ... & Zhang, G. (2024). Complexity of avian evolution revealed by family-level genomes. Nature, 629(8013), 851-860.
Tambussi, C. P., Degrange, F. J., De Mendoza, R. S., Sferco, E., & Santillana, S. (2019). A stem anseriform from the early Palaeocene of Antarctica provides new key evidence in the early evolution of waterfowl. Zoological Journal of the Linnean Society, 186(3), 673-700.
Image credits – Crown-Aves
- Header (Roseate spoonbill, Platalea ajaja, photographed in the Tárcoles river, Costa Rica): Kpts44, CC0, via Wikimedia Commons.
- Figure 3 (Conflicto antarcticus): Tambussi, C.P., F.J. Degrange, R.S. De Mendoza, E. Sferco, and S. Santillana., CC BY 2.5 <https://creativecommons.org/licenses/by/2.5>, via Wikimedia Commons.