Molecular phylogenetics: Big birds don’t always flock together

If you had to think of the biggest bird you know, you’d probably conjure up an image of an ostrich (Struthio camelus).

Ostrich

If you have some familiarity with Australian fauna, the emu (Dromaius novaehollandiae) might also come to mind.

EMU_

If you’re a bird watching champion back home, you might even know about the cassowaries (Casuarius spp.) and the rheas (Rhea spp.).

Casuarius_casuarius_-Emmagen_Creek,_Queensland,_Australia_-adult_and_chick-8Rhea,_Greater_male_ClaudioTimm

Looking at these birds, it’s probably not difficult to see some similarities. I’ve heard children at zoos call rheas “ostriches” due to their obvious similarities (I’ve probably heard adults say the same thing). These birds are all large, have massive, powerful legs and are flightless, perhaps necessarily, with reduced or even completely absent wings. Besides these and other traits, these giant birds share what is called a palaeognathous jaw, which is more reptilian than most other birds. This gives them their scientific name: the “palaeognaths” (palaeo = “old”, gnathous = “jaw”).

The only other living palaeognaths are the much smaller kiwis (Apteryx spp.) and tinamous.

kiwibirdgenotinamou

Kiwis are similar to other palaeognaths in that they cannot fly, but tinamous do, although they have a tendency not to. Think of tinamous as the palaeognath equivalent of a quail.

As one might expect, the DNA of the large-bodied palaeognath species is more similar to each other than to, say, ducks or finches. However, despite being very quail-like, tinamous group with the ostrich-like birds. This shouldn’t be terribly surprising from an evolutionary perspective given that they share some anatomical characters, such as the palaeognathous jaw. However, what is strange is that tinamous are genetically nested (no pun intended!) deep within the palaeognaths.

Palaeognaths-page-001

Above is a part of molecular phylogeny from Prum et al. [1], in which the authors estimated relationships of these (and many other) bird species using over 390,000 letters of DNA. Branches representing tinamous are in gray, with other palaeognaths in black. Even though tinamous look more like quails than emus, they’re much more genetically similar to the latter. In fact, emus, cassowaries, and the rhea are all more genetically similar to tinamous than they are to the ostrich. This suggests that tinamous evolved from a large-bodied ancestor, or various palaeognaths repeatedly evolved large body sizes and flightlessness.

Questions for Creationists

Why would such tiny, quail-like birds be so genetically similar to large birds like ostriches and emus rather than quails or chickens? If God created birds’ DNA, and their DNA determines what they look like, why do birds that look so radically different have similar DNA? If these species all evolved from a  common ancestor rather than being directly created, what else might you expect them to have in common?

References

1. Prum, R. O., Berv, J. S., Dornburg, A., Field, D. J., Townsend, J. P., Lemmon, E. M., & Lemmon, A. R. (2015). A comprehensive phylogeny of birds (Aves) using targeted next-generation DNA sequencing. Nature.

Photo credit

OstrichEmuCassowaryRheaKiwiTinamou

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2 thoughts on “Molecular phylogenetics: Big birds don’t always flock together

  1. Pingback: Biogeography: Palaeognaths all live(d) on southern continents – Evolution For Skeptics

  2. Pingback: Where did the lithornithids go? – Evolution For Skeptics

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