no? yes? does it really matter . . . and I know that this thread has been off topic for a while but whatever.
You are absolutely right about apes and humans coming from a common antecedent. While there is no doubt an amphibious animal was the common antecedent of all land animals, the differences between them and us are so enormous that it is not correct to say we were amphibious mammals. The human race evolved not from an amphibious creature, but from an ape-like creature from which anthropod apes and human beings are decended. Orientation of body hair (who came up with that one) and the shape of our bodies has very little to do with some remote amphibious creature.