Sea gulls: transitional between crows and cranes + hummingbirds + penguins

As we’ve seen over and over
phylogenetic analysis (subset of the LRT in Fig. 3) lets us see behind the curtain of prehistory, revealing evolutionary pathways and relationships that have been largely obscured by phylogenetic miniaturization, convergence and other factors.

Figure 1. Corvus the crow is basal to a long list of taller and shorter birds.

Figure 1. Corvus the crow is basal to a long list of taller and shorter birds. Compare this taxon to the sea gull in figure 2.

Today,
the black-headed sea gull (Chroicocephalus ridibundus; Linneaus 1766; 40cm long; Fig. 2) nests between crows (Fig. 1) and terns and basal to cranes + stilts + hummingbirds and kingfishers + penguins. When you look closely at it (and run the numbers) it really does look like a generalized white crow on its way to creating descendants that would be the most specialized of all birds. 

Figure 1. Chroicocephalus, the black-headed sea gull in vivo and as a skeleton.

Figure 2. Chroicocephalus, the black-headed sea gull (or white crow!) in vivo and as a skeleton.

Sea gulls are so generalized
that there is little about them that creates headlines. But that’s exactly what we (and PAUP) look for when we’re looking for basal and transitional taxa.

Figure 2. The clade of (chiefly) extant birds (Euornithes) with the addition of several taxa including Chroicocephalus, the sea gull (n the pink clade). Chroicocephalus = sea gull. Archilochus = hummingbird. Aptenodytles = penguin.  Grus = crane. 

Figure 3. The clade of (chiefly) extant birds (Euornithes) with the addition of several taxa including Chroicocephalus, the sea gull (n the pink clade). Chroicocephalus = sea gull. Archilochus = hummingbird. Aptenodytles = penguin.  Grus = crane.

The way the LRT is nesting taxa here
(Fig. 3) is creating a different topology from traditional studies. And it suggests a deep, deep radiation extending deep into the Cretaceous, not the Early Tertiary.

References
Linneaus C von 1766. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio duodecima, reformata. pp. 1–532. Holmiæ. (Salvius)

wiki/Black-headed_gull

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