Short answers, pulled from the story.
All pinnipeds descended from a single ancestor that split from other caniforms approximately 50 million years ago during the Eocene epoch. Molecular evidence from 2021 proved that all pinnipeds are monophyletic rather than descending from separate ancestral lines. This ancient lineage began in the fresh waters of Arctic Canada where the fossil genus Puijila roamed.
Some species like the northern elephant seal dive over 1,000 meters deep for more than an hour. Their circulatory system contains retia mirabilia to store oxygen and blood that can hold up to 20% of their body weight in hemoglobin and myoglobin. This physiological adaptation allows them to survive the hypoxic conditions of the deep ocean.
The walrus possesses the most vibrissae of any pinniped with 600 to 700 individual hairs. These whiskers allow the animal to locate bivalves on the ocean floor and detect hydrodynamic trails left by fish minutes after they have swum away. This tactile system can replace vision in darkness and helps seals navigate through pitch-black depths.
The Caribbean monk seal and the Japanese sea lion became extinct in the past century due to relentless commercial hunting and competition with fisheries. The Caribbean monk seal was considered extinct by 1996 after as many as 100 seals were slaughtered in a single night by European settlers. The last recorded individual of the Japanese sea lion was a juvenile captured in 1974.
The International Union for Conservation of Nature recognizes 36 pinniped species with ten more considered at risk. Threats include accidental entanglement in fishing nets, marine pollution, and the impacts of climate change on sea ice. Species like the harp seal and ringed seal face increased death rates due to breeding on thin ice.