Short answers, pulled from the story.
Pakicetus lived approximately 49 million years ago during the Middle Eocene in Pakistan. This wolf-sized creature possessed functioning legs, carnivorous dentition within a long snout, and represents one of the oldest members of ancient cetaceans.
There are roughly 90 living species split between baleen whales and toothed whales. Toothed whales include 75 species such as porpoises, dolphins, beaked whales, belugas, and sperm whales that possess teeth evolved to catch fish or squid.
Sperm whales hold the largest brain mass of any animal on Earth with an average weight of 6 kilograms reaching 9 kilograms in mature males. These brains contain elongated spindle neurons previously known only in hominids until 2019.
Commercial whaling of 14 large species was prohibited from 1985 to 2005 though some countries do not honor this ban. Norway and Iceland continue commercial operations while Japan hunts under scientific research pretexts.
Underwater noise impairs communication and sense of direction causing panic driving animals to the surface rapidly. This leads to bubbles forming in blood gases resulting in decompression sickness and fatal injuries when naval exercises use sonar regularly.