Friday, June 1, 2012

Convergence and Confusion

I went to the Stone Zoo yesterday and had a great time checking out some interesting animals.  They have a really nice collection, skipping a lot of the usual more showy African animals but including a few black bears, a lynx and a set of Tibetan steppe animals and South American animals.  They generally seemed healthy and active which is always good to see.  The highlight of the day, by far, was their bird show.  Mostly the birds were raptors including a very nice looking bald eagle that I was able to get very close to at the end of the show.  Which...y'know is really cool to see such a big bird that close.

But maybe the coolest bird was their red-legged seriema.  This unusual bird hardly ever flies but rather runs or walks and has a very interesting hunting behavior.  They will grab small animals, usually reptiles, by the tail and then smash them into the ground.  You can find an image of this here.  I wanted to learn a little more about this bird, and couldn't quite remember the name after getting home from the zoo so I consulted a large bird book I've got.  I immediately assumed it was a crane relative due to its long legs and found it there with the other cranes.  Apparently I have an eye for sorting birds into families.

Except really I don't.  This is the really interesting thing about living in a time that we have access to molecular data in regards to phylogeny.  For hundreds, really thousands, of years scientists and natural historians have been sorting animals based on how they look.  It makes sense, of course, that animals that look very similar should be closely related.  And much of the time this is correct.  All insects with a set of wings and a set of hard, protective wing coverings are all coleoptera, everything with a soft, shell-secreting body is a mollusk.  However we forget that birds are tiny subgroup of an already small subphylum and so when you get that specific weird things begin to happen.

Over the course of talking about several of the animals we saw I found myself examining a mammal and bird phylogeny really closely.  I'll talk about the bird phylogeny but you can check out the mammal one here.  So a few things to notice on the bird phylogeny here.  (If you're not familiar with how to read cladograms, basically each fork represents a common ancestor and the lengths of the lines represent time so the longer the line, the longer that group has existed and the closer one group is to the fork of another, the more closely they are related).  So first find the seriemas.  They are actually not cranes at all.  They are what we call a sister group (i.e. the group on the other side of a fork) with a group containing parrots, falcons and the group called passerines, which are all perching birds (basically all yard birds...mainly small birds with gripping, perching feet).  Something else to point out here, falcons are not the same thing as hawks or owls, each of these three bird families are spread fairly far out on the tree.  The falcons being placed with parrots and passerines is something very new, I found an article from Tetrapod Zoology written just last month describing the new molecular data and the reorganization of the clades.

The fact that falcons look just like small hawks and owls really resemble hawks, at least in terms of beak shape and talon shape, is what we call "convergence."  When organisms fall into a similar niche in the ecology (i.e. they are getting their food and living their lives in similar ways) more often than not then evolve to look very similar.  It makes sense.  If you have two families of birds that are hunting other vertebrates they are both going to want to be fast and they are going to want to have very sharp beaks and talons.  And that's exactly what you find.  Even though hawks and falcons are NOT sister groups they look the same because they have both evolved to utilize other vertebrates as energy sources.

So I've rambled pretty long about phylogeny here (it's probably my most nerdy passion) but a few more really interesting things to point out on the bird tree.  Herons, storks and cranes...all different things.  More convergence.  And the most surprising thing (to me)?  Find loons, grebes, and ducks.  All different things.  A grebe's most close relative is a flamingo!  Ducks are also found all the way across the phylogeny from most other shore birds, found in blue.  They are actually most closely related to things like pheasants and quails.

One final note.  I'm now a huge fan of the seriema.  I think they're really cool, very dinosaur-like birds.  One thing I found in my research: scientists now believe their closest relatives where the terror birds.  Which, if you're not familiar with, you should be.  You can start here.

OK, I'm finally done ranting about convergence.  Enjoy learning about terror birds!

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