Hearts in amphibians, reptiles, birds, and mammals

This diagram "zooms in" to show just the fate of the aortic arches in amphibians, reptiles, birds, and mammals. The diagram clearly indicates (unlike the diagram in Explore Evolution) that the only fundamental topology change between reptiles and mammals is that mammals have lost the right systemic arch. From Figure 12-20, p. 462 of: Kardong, Kenneth V. (2006). Vertebrates: comparative anatomy, function, evolution. Boston, McGraw-Hill Higher Education.