In the development of a mammal there are three stages of erythrocyte formation---one of them, the adult erythrocites, are the most common blood cell type in mammals, and their characteristi bioconcave shape, diameter and ennucleation are amonst the greatest commonalities between mammalian species.
Throughout the development of a mammal, there are three distinct stages of erythrocyte formation  embryonic, fetal and adult. Adult erythrocytes are the most common blood cell type in mammals, and their characteristic biconcave shape, 7-8 m diameter and enucleation are amongst the greatest commonalities between mammalian species. 
