AlphaOmegakid writes:
Now you did a good job searching the internet for some science on the subject, But this science says zero about how this process evolved. That is my question. Do you have an answer?
I do. By mutation and selection, natural processes known to exist, unlike this Jesus character you mention in the O.P.
More specifically, and for part of the story, the duplication of a gene and its subsequent mutation seem to have added a key component to erythrocyte spectrin, which is a key to the functioning of mammalian red blood cells in the absence of new protein synthesis.
As you're interested in the subject, you'll enjoy this:
Some analysis of one aspect of mammalian RBC evolution
Apart from that, your objections in the O.P. would be met by the fact that the ancestral reptiles already had the features of RBC production and circulatory organs necessary to cope with the changes in the mammalian system.