In the Paleogene the seas were dominated by early Procellariidae, giant penguins and two extinct families, the Pelagornithidae and the Plotopteridae (a group of large seabirds that looked like the penguins).
The highest diversity of seabirds apparently existed during the Late Miocene and the Pliocene.
Most species nest in colonies, which can vary in size from a few dozen birds to millions.
Many species are famous for undertaking long annual migrations, crossing the equator or circumnavigating the Earth in some cases.
They feed both at the ocean's surface and below it, and even feed on each other.
Seabirds can be highly pelagic, coastal, or in some cases spend a part of the year away from the sea entirely.
Seabirds and humans have a long history together: they have provided food to hunters, guided fishermen to fishing stocks and led sailors to land.
They are first known to occur in the Cretaceous period, the earliest being the Hesperornithiformes, like Hesperornis regalis, a flightless loon-like seabird that could dive in a fashion similar to grebes and loons (using its feet to move underwater) While Hesperornis is not thought to have left descendants, the earliest modern seabirds also occurred in the Cretaceous, with a species called Tytthostonyx glauconiticus, which seems allied to the Procellariiformes and Pelecaniformes.These evolutionary forces have often caused species in different families and even orders to evolve similar strategies and adaptations to the same problems, leading to remarkable convergent evolution, such as that between auks and penguins.There are four basic feeding strategies, or ecological guilds, for feeding at sea: surface feeding, pursuit diving, plunge diving and predation of higher vertebrates; within these guilds there are multiple variations on the theme.Wing morphology has been shaped by the niche an individual species or family has evolved, so that looking at a wing's shape and loading can tell a scientist about its life feeding behaviour.Longer wings and low wing loading are typical of more pelagic species, while diving species have shorter wings.