Final answer:
Prehistoric pit houses in the American Southwest were primarily oval and circular in shape, built partly underground to suit the extreme climate. Over time, Ancestral Puebloans created larger multi-storied buildings and kivas as part of their settlements.
Step-by-step explanation:
In prehistoric pit houses in the American Southwest, a variety of shapes such as oval and circular are found. These early settlements consisted of pit houses that were partly underground, constructed with wooden poles and dried mud. Designed for the hot climate, the pit houses had openings for ventilation and ladders for access. Over time, the architectural complexity increased, and the Ancestral Pueblo peoples began constructing large multi-storied buildings and cliff dwellings with intricate masonry in places like Mesa Verde, as well as ceremonial centers known as kivas.