Final answer:
Nucleated red blood cells (nRBCs) are typically found in the peripheral blood of birds and non-avian reptiles, as opposed to mammals, whose mature red blood cells do not contain nuclei.
Step-by-step explanation:
Nucleated Red Blood Cells in Different Animal Species
Nucleated red blood cells (nRBCs) are typically found in the peripheral blood of certain vertebrate species. While mammalian red blood cells, such as those in dogs and cats, lack nuclei at maturity, other vertebrates maintain nucleated erythrocytes throughout their lifespan. Notably, the red blood cells of birds and non-avian reptiles are characterized by the presence of a nucleus. These nucleated red blood cells are typically larger, aerobic, self-replicating, and relatively short-lived compared to the anucleate, long-lived erythrocytes found in mammals.
Therefore, nRBCs are typically recognized in the peripheral blood of birds and reptiles, in contrast to mammals such as dogs, cats, horses, and ruminants, where the mature erythrocytes circulating in the blood do not contain nuclei. This distinction is vital in understanding the physiological differences in oxygen transport and cellular maturation between mammalian and non-mammalian vertebrates.