The story
Pinnipeds, the group of seals, sea lions and walruses, evolved from bear-like carnivorans in the North Pacific. Enaliarctos mealsi, described from Oregon and California in 1973 by Edward Mitchell and Richard Tedford, lived about 27 to 24 million years ago. It had four flippers, a body suited to swimming, and teeth for catching fish, but it could still move on land. In 2009 Natalia Rybczynski and colleagues reported Puijila darwini from the Canadian Arctic, an otter-like animal from about 23 million years ago that retained walking feet with webbing.
The cold Oligocene and Miocene North Pacific was rich in fish and squid, and marine mammals could exploit it. The fossils show a step-by-step transition, with early forms like Enaliarctos using both fore and hind limbs for swimming while later seals rely on the hind limbs and sea lions mostly on the fore limbs. Pinnipeds share a single common ancestor, a question that was debated for a long time, and DNA shows that their closest relatives are bears and weasel-like carnivorans. Seals and sea lions radiated across the world's cooler coasts, and later whales and pinnipeds were prey for large sharks.
Why it mattered
- Pinnipeds are a well-documented case of mammals re-entering the sea, like whales but independently.
- They became major predators in polar and temperate seas, shaping marine food webs.
- Their fossil record helps explain the evolution of flippers and swimming locomotion in mammals.
Sources
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