Because their brains needed a lot of oxygen... maybe?
*
But no. Apparently, it's because they couldn't bend their head upward. So when drinking from a pond, they had to submerge their entire snout to do so. If their nostrils were on their snout, it would have made them unable to breathe while drinking.
*
But no. Apparently, it's because they couldn't bend their head upward. So when drinking from a pond, they had to submerge their entire snout to do so. If their nostrils were on their snout, it would have made them unable to breathe while drinking.