Final answer:
Camels are the species with elliptical RBCs, which is an adaptation to their desert habitat.
Step-by-step explanation:
The species that has elliptical RBCs (red blood cells) among the options provided is D) Camel. Most mammalian red blood cells are biconcave and do not have nuclei in their mature form. This is different from birds, for example, whose red blood cells do have nuclei. Compared to other mammals, camels have elliptical-shaped RBCs, which are thought to be an adaptation to their dehydrating desert habitat, helping the cells flow more easily when the body is dehydrated and the blood becomes thicker.