The kagu and the tern: you can almost tell by their ‘haircuts’

Figure 1. Thalasseus the created tern nests with Rhynchetos, the kagu.

Figure 1. Thalasseus the created tern nests with Rhynchetos, the kagu with an even larger crest (figure 2).

Figure 2. Finding the skeleton of the kagu, Rhynochetos, was helpful in properly nesting this taxon.

Figure 2. Finding the skeleton of the kagu, Rhynochetos, was helpful in properly nesting this taxon.

Wikipedia reports:
on the kagu: The kagu’s affinities are not well resolved. It was long one of the most enigmatic birds and in more recent times is usually affiliated with the Gruiformes (cranes). It was initially classed as a member of the clade Ardeidae (herons) because of the presence of powder down, similarities in plumage colour and internal anatomy, the colour of the chicks and eggs, and the change in colouration of the chick as it grows. When seen as a gruiform, the kagu is generally considered related to the extinct adzebills from New Zealand and the sunbittern from Central and South America. Recent studies do indicate that the sunbittern is the closest living relative of the kagu.

Figure 3. Skeleton of Thalasseus, the crested tern.

Figure 3. Skeleton of Thalasseus, the crested tern.

With the recent revisions going on
at ReptileEvolution.com in the higher bird clade the kagu (restricted to the island of New Caledonia) now nests with the tern (Indo-Pacfic oceans, including breeding on New Caledonia and along the coasts elsewhere). And now we know how the kagu got to New Caledonia in the first place. More data (Fig. 2) and a closer examination of existing data are making these moves.

Thalasseus bergii (aka: Sterna bergii; Lichtenstein 1823; 50cm tall) is the extant greater crested tern is a sea bird capable of flying great distances and feeding by plunge diving. Terns are traditionally related to gulls, skimmers and skuas. Here the resemblance toRhynochetos extends to the head crest.

Rhynochetos jubatus (Verreaux and DesMurs 1860; 55cm in length) is the extant kagu, a nearly flightless sea gull restricted to New Caledonia. The rostrum tips down and is sharp. ‘Nasal corns’ (soft structures covering the nostrils) are a unique feature presumably developed to prevent dirt from entering. Perhaps these were originally developed by the extinct tern ancestor that used them to prevent water from entering during dives. ‘

The large reptile tree higher bird subset is under thorough reexamination presently. Yesterday’s post on pigeons and vultures is part of this.

References
Lichtenstein M 1823. Published in:Lichtenstein, H. 1823, pp. x 118 pp., Königl. Universität, Berlin
Verreaux JP and des Murs O 1860. Descriptions d’Oiseaux nouveaux de la Nouve.-Calédonie.

wiki/Rhynochetos
wiki/Greater_crested_tern

 

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6 thoughts on “The kagu and the tern: you can almost tell by their ‘haircuts’

  1. No, of course not. That’s just icing on the cake. I can send you the .nex files. It’s the suite of traits, some of them convergent, some of them down to the width of pedal digit 3 vs. 4 that the two share most parsimoniously together to the exclusion of all other 1140+ taxa.

    • Well I’m not qualified to argue over the fine details, I’m afraid. But the key is surely how you distinguish convergent from inherited characters. Just what is and what isn’t labile. To take you example, why exactly do you think that relative pedal digit width should be a conservative character?

  2. The beauty of the software is it’s lack of bias. It doesn’t think about a relationship, it breaks things down to numbers. Convergent traits are truly rampant in the LRT, so the conservative trait can change in derived taxa. The example of a thinner digit 4 compared to 3 comes and goes and comes and goes, etc. etc. The same for most of the traits. That’s why I suggest that clades not be defined by traits, but by common ancestors only. Only rarely, like the origin of feathers, or the amnion, does a trait continue throughout a clade. A good example is Ankylosaurus, which lacks an antorbital fenestra, a trait common among other dinosaurs. Does that clarify or muddy things for you?

    • I can see how traits may appear and disappear as their genes are switched on and off by changes in selective pressure during the course of evolution, not to mention all kinds of ways by which similar anatomical structures may be derived in parallel. But I confess it’s not clear how clades might be distinguished at all, once the classical approach has been abandoned. I would need to study the (statistical?) principles behind your software. Can you provide a link to an overview of the method?

  3. I use MacClade to enter data. Mesquite does the same job with modern graphics. I use PAUP to analyze data. Mesquite, I’m told, does this with Zephyr, evidently a modern version of PAUP. After that I can only suggest Wikipedia and the product’s websites for more information.

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