This week I went to a talk at Zoology on Palaeognaths.
(I spent much of the week guessing what Palaeognaths were... I knew I'd seen the term in the museum... was it the research on fins to limbs? Or early jaws... does that translate as early jaws? Is this the emergence of the first sharks? No.)
Palaeognaths, also called the Ratites, are the big lumpy flightless birds that I think of as the most dinosaur-y: Ostriches, Emus, Rheas, Cassowaries... and the extinct Moas and Elephant birds. All giants, with big kicking feet, and all living lives that help me imagine the answer to the question "How did T. Rex cope with tiny useless forearms?" with "try living with tiny useless wings instead!" Though the series of cartoons by Hugh Murphy (some shared on SadAndUseless) helps bring the T-Rex problems to life too.
So, these tiny winged, big legged, giant flightless birds. They all live in the Southern Hemisphere - pretty much on all the bits that made up Gondwanaland before it broke up. And they evolved from dinosaurs, which was sort of Gondwanaland time and such, wasn't it.
So, their evolution story seemed quite straight forward. What paleontologists like to call the Gondwana Vicariance Hypothesis
There's a couple of footnotes to add about the oddities - there are the New Zealand kiwis in the same family, but that's okay, they're flightless too, and lay ridiculously large eggs for such a tiny bird, so maybe they started as giants and shrunk. There's also the tinamous in there. A bunch of birds that look a bit like grouse, living in South America, and they can fly! But that's okay, lots of birds learned to fly after dinosaur times... the theory is looking fine.
Then they did some genetic analysis of the bird groups - all still rosy, each of the living groups are a separate branch. But then they analysed the DNA of the extinct species - and it all went pear shaped!
The flightless huge Elephant bird known only in Madagascar is not that closely related to the flightless massive Ostrich in Africa. It's closest relative is the little dinky flightless kiwi of New Zealand.
Blistering Barnicles!
Meanwhile the ginormous Moa of New Zealand is most closely related to the small flying Tinamous of South America.
Blistering Buggering Barnicles!
Oh, and they diverged from each other around 70 million years ago, whereas Gondwanaland broke up around 140 million years ago.
Billions of Blistering Buggering Barnicles!
So, what happened?
Well, the story seems to start with the very common stone bird, Lithornithidae. Sometime around 70 million years ago, they figured that their dinosaur cousins had all died, and the whole world was full of very tasty fruit and seeds not being eaten. So, before the mammals could come along and grow big and fat on it, they flew all over the world to take up those big, yummy ecological niches.
And, just to make the story more complex, they all came from the Northern Hemisphere (Laurasia, as was).
So they all flew south, and, most (but not the tinamous) then lost the power of flight, and most (but not the kiwis) grew big and fat and huge on the fruit and seed diet so that when mammals finally figured it was safe not to be rat sized anymore, these birds were mostly already too big to be taken on, so settled safely into their lifestyles for 60 millions years or so, waiting for their confusing family tree to be unravelled. This is how we think they are related now, and where they live (or lived).
So, whenever anyone asks you to give them a simple, straight forward account of evolution, be prepared to explain that it is often a "little more complicated" than they might think! (For other accounts of the palaeognath evolution story, probably with more of the science bit, see "the case of the flying kiwi" and "flight of the ratites")
For skeletons of ratites and other birds, I'm currently helping the Museum of Zoology condition report a bunch of skeletons, which I'm sharing here.