In what direction was the evolution of erythrocytes in vertebrates?

Let’s take a look at the example of a person and our blood cells. We have small red blood cells that resemble a disc. Also, these cells are devoid of various organelles, including the nucleus. They are made up of hemoglobin, which carries oxygen. Accordingly, the more hemoglobin occupies the structure of the erythrocyte, the more oxygen will be transferred through the body. It is up to this decrease in erythrocytes, the disappearance of organelles in their structure, and the evolution of vertebrates strives, since these are complex organisms that need a large amount of oxygen.