The conclusion is that the A was probably tree dwelling?
How is it supported? The A had claws that enable modern tree dwelling birds to perch in trees.
So, the whole conclusion depends on the type of claws A has, and what the ornithologist knows those claws are used for today. It must be the case, therefore, that the A used those claws or else the only support we have for the conclusion would be gone. This is why B must be assumed. If the A didn't use its claws, we have no basis for concluding what kind of bird A was.
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The conclusion is that the A was probably tree dwelling?
How is it supported? The A had claws that enable modern tree dwelling birds to perch in trees.
So, the whole conclusion depends on the type of claws A has, and what the ornithologist knows those claws are used for today. It must be the case, therefore, that the A used those claws or else the only support we have for the conclusion would be gone. This is why B must be assumed. If the A didn't use its claws, we have no basis for concluding what kind of bird A was.