Question

The order Cetacea includes modern-day whales, dolphins, and porpoises. These marine mammals share common characteristics that have led scientists to make a conclusion about their evolutionary history. Cetaceans:
lack gills and must breathe air
give birth to live young rather than lay eggs
have fin bones that are similarly shaped to limb bones
have spines that flex up and down rather than side to side
The characteristics of cetaceans provide evidence that
A.
the bodies of their ancestors never changed.
B.
they evolved from land mammals.
C.
the theory of evolution is incorrect.
D.
they evolved from air-breathing fish.

Answer 1

B. they evolved from land mammals.

Evidence: breathing air, bearing live young, limb bone homologies in fins, and an up-and-down spinal flexion pattern are all mammalian traits that indicate cetaceans descended from terrestrial mammals (fossils such as early archaeocetes show transitional stages). The other choices are inconsistent with these traits.