Of course, but we are doing a theoretical mind game here. Because, in theory, it could be possible tht the descendants of a cow would be just like birds. And when I say just like birds, I mean externally and internally, and the only differences that would be present would be on the same scale as birds have between one another.
Would it still have to be called a cow ?
There are two possibilities:
1) There is no evolutionary possible path from current cows to anything even a bit like a bird.
If I had to choose I'd say that this is the case but there is no way that I can think of of knowing.
That is, the odds are actually zero. Period -- zero.
2) There is a path but it has a pretty small but not calculable probability.
This is also a "I don't know" path. Again if I had to choose I'd pick an utterly astronomically small likelyhood but still admit it isn't calculable.
If it looked just like a bird in all ways then a taxonimist would have nothing to go on to classify it as anything but a bird. However, by the definition of clade (as I understand it) s/he would be wrong.
The difference between a creationist's answer to this and that of a biologist now becomes a joke. Who cares if the creationist say chance of the path "theoretically" described is zero and the biologist says it can't happen by normal evolutionary processes in 10 universe lifetimes. The difference between the two views is close enough to zero.
However, why make up silly things to discuss?
As noted we have real world examples in convergent evolution.♠
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