Acrophoca longirostris (Muizon 1981, Late Miocene. 1.5m) is the 'swan neck seal'. According to Wikipedia, "It was thought to have been the ancestor of the modern leopard seal; however, it is now thought to be a species of monk seal. Its teeth were built for piercing, implying a diet consisted primarily of fish. However, it also had interdigitated tooth cusps causing the teeth on the upper jaw to fit with the teeth of the lower jaw, which is consistent with filter feeders. Unlike other earless seals, Acrophoca had a long and flexible neck, with an elongated body. The orientation of the pelvis, which in comparison to modern earless seals is everted, as well as adaptations to the hind limbs suggest that swimming was mainly powered by the back flippers."

Here Acrophoca nests with extant Eupleres (above), so may be convergent with extant seals and sea lions. Note the large naris and small orbit.

Neotherium mirum (Kellogg 1931; Middle Miocene) was originally considered a small, tuskless walrus, but here nests basal to sea lions. The molars are premolarized.

Enaliarctos mealsi (Mitchell and Tedford 1973; Late Oligocene, 24 mya; 1m in length) was considered the oldest known pinniped, but here nests with Desmatophoca and other sea lions. Here the manus remains smaller than the pes. The molars were transformed into premolar shapes.

Desmatophoca oregonensis (Condon 1906; Early Miocene; skull length 31cm) was considered closely related to the seal Phoca, but here nests with the sea lion Enaliarctos. The molars are premolarized. The cranium was round, not crested. The premaxilla was transverse.

Pithanotaria starri (Kellogg 1925; Miocene, 10mya) is very similar to the modern eared seal (sea lion).

Zalophus californianus (Gill 1866; extant) is the California sea lion. Limbs are transformed into flippers in this swimming carnivore. This piscivore is wrapped in a thick coat of blubber (fat) that insulates it and streamlines its body contours.

Seals are diphyletic. Marine forms had separate terrestrial ancestry. Phoca is an earless seal (family: Phocidae) derived from a sister to Paleaosinopa. Zalophus is an eared seal (family: Otariidae).

According to Wikipedia: "Otariids use their front limbs primarily to propel themselves through the water, while phocids and walruses use their hind limbs. Otariids and walruses have hind limbs that can be pulled under the body and used as legs on land. By comparison, terrestrial locomotion by phocids is more cumbersome. Otariids have visible external ears, while phocids and walruses lack these."