Life in the
Oligocene oceans looked increasingly familiar. Fossil pinnipeds
(seals and sea lions) first appeared in the late Oligocene seas, looking
much like their modern descendants. Whales had evolved
into the two suborders present today, the toothed whales (odontocetes)
and baleen whales (mysticetes). These marine mammals
lived alongside sea cows and increasingly modern shark species. Bony
fishes thrived as well.
Marine invertebrates, too, took on a more familiar appearance. In
the warm tropical seas, carbonate shell reefs extended as far north
as North Carolina. Similarly, coral reefs developed
in the Southern Hemisphere as far south as northern New Zealand. Nummulitid
foraminiferans were common, and the first irregular
echinoids (sea urchins) were present. Other major
invertebrate groups included cephalopods (squid and
octopus), bivalves, snails, and crustaceans.