Short answers, pulled from the story.
The transition from land to sea began approximately 49 million years ago when primitive cetaceans first entered the water. These ancient ancestors, known as archaeocetes, split from a common lineage with Indohyus around that same time.
By 35 million years ago, Basilosaurus had moved its nasal openings to the top of the cranium and modified forelimbs into flippers. Hind limbs eventually shrank and disappeared entirely by 34 million years ago, leaving only vestigial pelvic bones in modern species.
A bottlenose dolphin develops its whistle during its first year and maintains it throughout life. Some individuals relate to signatures from others they have not seen for over twenty years.
Cooperative human-dolphin fishing partnerships operate today in Laguna Santa Catarina Brazil where dolphins signal fishermen to cast nets. This technique spreads within generations rather than passing directly from mother to daughter.
The Yangtze river dolphin appears functionally extinct following a 2006 survey finding no individuals due to pesticides heavy metals plastics and industrial pollutants concentrating in predators like dolphins causing injuries or death.
Wild males survive 31 years on average but captive ones rarely exceed 50 years while life expectancies for captive females average into their 20s versus 46 years for wild females.