- The diagram shows the evolutionary tree of 726 extant waterbird species. This group of birds belong to a clade called Aequorlitornithes whose most recent common ancestor (MRCA) existed 64 million years ago (Mya). 339 of the listed species spend most of their lives in a marine environment. In fact, all of today’s seabirds are Aequorlitornithes.
- 11 bird Orders are represented in Aequorlitornithes. These clades are indicated by colour. The largest is Charadriiformes with 369 species. Shading highlights Family groups within each Order. 13 of 39 families present are pure seabird clades. These include albatrosses (Diomedeidae), penguins (Spheniscidae), storm-petrels (Oceanitidae and Hydrobatidae), auks (Alcidae), skuas (Stercorariidae) etc. The oldest family is the tropicbirds (Eugygypimorphae) with MRCA of 58Mya. Other waterbirds present such as gull and terns (Laridae) are not normally classed as seabirds. One family (sandpipers, Scolopacidea) contains a single genus (phalaropes) that are considered a true seabird. While most Aequorlitornithes are associated with water, there are exceptions e.g. stone-curlews (Burhinidae), plains wanderer etc.
- The blue circles on the leaves of the tree indicate “evolutionary distinctiveness” (how long ago a species split from its closest living relative). According to this phylogeny, the red-billed tropic bird is the most distinct seabird. The second most distinct seabird is the ringed storm-petrel South America (a South American member of Hydrobatidae). Gulls tend to be least distinct. The most distinct gulls are Ross’s and the Swallow-Tailed Gulls.
- A square root transformation of the time axis that runs from the centre (64Mya) to the perimeter (present day) is used to show the early branching identified by Prum et al (Ardea etc) more clearly.
- Highlighted species names are those that I have photographed to date in my personal record. Corresponding branches of the evolutionary tree are shown as solid lines.
- The diagram was created using data from four different sources (1) ebird current list of 13,727 bird species and subspecies with current classification (2) Prum et al phylogeny of 198 birds (all bird orders and 127 out of 251 families represented) which resolved early splits in the avian tree including the Aequorlitornithes (3) detailed phylogenies at family level from birdtree.org (9993 species). These were rescaled and grafted on to the Prum et al‘s phylogeny to create the above tree. Birdtree and Prum et al are not compatible. Where possible I followed the latter. (4) My personal bird list.
- The origin of seabirds is suspiciously close in time to the cretaceous boundary 66.043 ± 0.011 Ma.
- Phylogeny and tree diagram created using ape, tidytree, ggtree, tidyverse and picante R packages.
- Seabirds sorted by evolutionary distinctiveness distinctiveness according to this phylogeny are show in the table below. Needless to say, this is likely to change in future when more comprehensive genetic studies are completed.