Short answers, pulled from the story.
The German naturalist Johann Karl Wilhelm Illiger gave the name Pinnipedia to a distinct taxonomic unit in 1811. Modern science recognizes three living families within this group: Odobenidae, Otariidae, and Phocidae.
This ancestor diverged from other caniforms approximately 50 million years ago during the Eocene epoch. Their closest living relatives are musteloids such as weasels, raccoons, skunks, and red pandas.
Fossil genera like Enaliarctos and Puijila help trace the evolutionary path from land-dwelling ancestors to fully aquatic life. The fossil genus Puijila lived in Arctic Canada during the Early Miocene and resembled a modern otter.
Pinnipeds tolerate large amounts of lactic acid reducing skeletal muscle fatigue during intense activity. Retia mirabilia line trunk and limbs allowing greater oxygen storage during extended submersion while hemoglobin stored in blood and myoglobin in muscles provide sufficient oxygen for long periods underwater.
As of 2021 International Union for Conservation Nature recognizes thirty-six pinniped species ten considered at risk. Hawaiian monk Mediterranean monk Galápagos fur Australian New Zealand Caspian Galápagos sea lions ranked endangered.