Problem:
Reading this question, I wondered why is it that we associate vertebrate venoms so often with snakes and fish, and more rarely with lizards, amphibians, mammals, and birds (apparently never, in birds?).
Question: Are venoms more advantageous for snakes and fish, or more expensive or dangerous to produce for the other taxa? Or is it connected to evolutionary history - is venom somehow more 'evolvable' for snake and fish lineages?
Or, perhaps, is it just chance?
Could someone help to explain the answer of these question.