Birds and feathers are synonymous now, but what prompted their evolution?
Photograph: Rodrigo Buendia/AFP/Getty Images
by Dr Dave Hone
A common creationist canard is the supposedly unanswerable “what use is half a wing?”.
Apparently there to confound biologists, what it generally does is demonstrate the ignorance of the asker with respect to evolutionary theory. However, the actual broader question that is inferred – what use is a feather to a non-flying bird? – is both relevant and interesting.
The earliest filamentous feathers appeared in dinosaurs well before birds ever did, and were present in plenty of species that had no hope of taking to the air (though I for one would love to see a flying tyrannosaur).
So then, what might their original function have been, and what prompted them to be maintained, grow larger and change over time?
The exact answer is sadly unknown. It is likely a number of factors in concert, or different ones having greater importance over others at various times, and piecing those fragments together is very tricky.
However, there are some strong leads and ideas, and for some feather types in some groups the answer is rather convincing.
To deal with the central issue though, there are in fact various things that feathers may offer animals aside from flight alone.
A quick look at living birds reveals plenty of possibilities, and almost all of them may be applied to various (or even all) dinosaurs that preceded true, powered flight.
There really are quite a few, so I’ll try to be brief, but it shows just how many selective pressures may have acted on feathers and led to their spread and development across the various dinosaurs that had them.