The major hematopoietic lineages have existed since early in vertebrate evolution, covering the key functions of oxygen transport, clotting and defense against infection. Some of the details of how these functions are performed are unique to mammals, such as using platelets formed from polyploid megakaryocytes for clotting rather than thrombocytes. Using single cell transcriptomes, we have created an atlas of gene expression of haematopoietic cells in mammals, chickens and fish, and annotated cells to their closest mammalian homologue by lineage. This has allowed us to look at how conserved haematopoietic gene expression is in different vertebrates in relation to human blood cells. We have identified genes which are conserved as signatures of blood and immune lineages across all vertebrates and genes which are only associated with mammalian haematopoiesis. We have then taken the mammalian specific and vertebrate conserved gene lists and looked at their regulation via ATAC-seq, and found that the more broadly conserved genes have more lineage specific open chromatin regions associated with them than genes with mammalian specific gene expression. This suggests that redundancy in regulation helps maintain lineage specific expression in divergent species.