Last week I gave you this mystery object to identify, found on a beach in Ireland:
It led to a lot of great cryptic comments relating to marine birds and sternum keels, but Lena was the first to comment and was spot on with the species (or at least as far as I can tell!)
Bird sterna are quite distinctive, with overall shape giving an indicator of mode of life. Long narrow but well-developed keels like this tend to be seen in marine birds that use their wings to fly underwater. The shape of the bottom and sides of the sternum tend to be quite specific to particular genera and species, making sterna pretty good for identification.
Of course that depends on having good comparative material and I was delighted to find John Rochester’s very helpful Flickr page, that has a comparison of British Auks (in this case we’re talking about the geographical British Isles rather than the sociopolitical concept of Britain).
If you take a look at those images you’ll notice that one fits the shape very well indeed – the Guillemot or Common Murre Uria aalge (Pontoppidan, 1763).
Guillemot with its meat and feathers on. Image by Dick Daniels, 2011
So that’s the identification I gave to Emer, Ronan, Rory and Paddy who found it on their hols!
Zygoma 
The cryptic clues were brilliant and we’re all I could use to keep me on the right track: many thanks to Lena et al who helped.
I would also like to add that the sternum in question brilliantly displays some of the qualities of engineering optimisation that evolution necessitates.
The keel has to be pretty solid to take the forces it encounters – powerful chest muscles to make wings beat.
The main body, not actually taking those forces, is as thin as it can become, lightening it as much as possible but keeping it solid, as the matrix can then take skew and even torsional forces as long as they are not too powerful.
Then the anchoring edges, connecting it to the rest of the rigid rib cage that most flying birds have (I think?), is also reinforced because it is through those that those forces are transferred to the rest of the bird, or from it.
Every time I read the late Professor J E Gordon’s classics (“The New Science of Strong Materials – or Why You Don’t Fall through the Floor” and “Structures”), coupled with anything evolution (most recently a re-read of Dawkins’ “The Greatest Show on Earth”), I am reminded of this intricate paring down of structures so that they do what they need to, but no more.
No wonder bio-mimesis is one of the hot fields in tech and engineering these days.
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