Final answer:
The whale ancestor exhibiting nasal opening migration and lateral eye positioning is Pakicetus, which along with Rodhocetus, represents transitional stages from land-dwelling to aquatic life in whale evolution.
Step-by-step explanation:
The first whale ancestor to exhibit the traits of a nasal opening shifting towards the back of the skull and eyes opening on the side of the head was Pakicetus. While there is still debate regarding how aquatic Pakicetus was, Rodhocetus is considered to have been a largely aquatic animal and also exhibits these traits. These evolutionary changes are part of the transition from land-dwelling to aquatic lifestyles, as witnessed in the fossil evidence of whale evolution. The transition includes adaptations such as hindlimbs becoming modified or reduced, indicating that modern whales once had ancestors with such limbs.
Whales evolved from terrestrial ancestors over millions of years, gradually adapting to a fully aquatic environment. This included morphological changes such as a backward migration of the nasal opening, allowing for easier breathing at the water's surface, and eyes on the sides of the head for improved field of vision underwater.