AP BIOLOGY

Detailed explanation-1: -The new bones, dubbed Pakicetus, proved to have key features that were transitional between terrestrial mammals and the earliest true whales. One of the most interesting was the ear region of the skull. In whales, it is extensively modified for directional hearing underwater.

Detailed explanation-2: -A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group. This is especially important where the descendant group is sharply differentiated by gross anatomy and mode of living from the ancestral group.

Detailed explanation-3: -Archaeopteryx is a transitional fossil because of its characteristics of both reptiles (dinosaurs) and birds. Basilosaurus and dorudon were ancient whales with tiny limbs and lived entirely in water. Ambulocetus is a more recent ancestor that had heavier leg bones and lived in both water and on land.

Detailed explanation-4: -Looking at a whale’s body and biology, there are plenty of clues that their ancestors lived on land. They breathe air and nurse their young with their own milk, they also have paddle-shaped flippers which encase hand bones with five ‘fingers’. As embryos, whales have tiny back limbs which disappear before birth.