Seems like if you read between the lines, there's a certain commonality in increased respiration/alertness, stress response and showing of teeth that solves a common need across species. When a subject recognizes a lack of alertness, a present threat or the need for aggressive action in the near future, a yawn can help prepare for that while also giving pause to those who might be threats and/or potentially paralyzing prey. The failure in consensus here appears, to me, an inability to describe those seemingly disparate needs as related to the physiology that drives them. Not a lack of understanding, so much as a deficiency in perlocution.