Plotopteridae

Plotopteridae is an extinct family of flightless seabirds from the North Pacific. Their powerful wings propelled them underwater, and fossils date from the Eocene to the Miocene.

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Wing-propelled diving: Underwater locomotion in which animals use their wings or forelimbs to generate thrust. Plotopterids used their wings to swim rather than fly.
Plotopterum: An extinct genus of plotopterid seabirds known from Miocene fossils in Japan. Its fossils provide a Japanese example of the family’s later history.
Eocene: A geologic epoch lasting from about 56 to 34 million years ago. Some of the earliest known plotopterid fossils date to this epoch.
Marine vertebrate extinction: The disappearance of fish, reptiles, birds, or mammals from marine ecosystems. Plotopterids vanished from the North Pacific fossil record by the Miocene’s end.
Flightlessness: The loss of powered flight in a lineage whose ancestors or relatives could fly. Plotopterids retained wings but lost the ability to fly.
Copepteryx: An extinct genus of large plotopterid seabirds known from Oligocene and Miocene deposits in Japan. Its species document substantial plotopterid diversity in the western North Pacific.
Oligocene: A geologic epoch lasting from about 34 to 23 million years ago. Many plotopterid fossils come from Oligocene marine deposits.
North Pacific: The northern part of the Pacific Ocean and its surrounding coasts and islands. This ocean basin contains the known fossil range of Plotopteridae.
Convergent evolution: The independent evolution of similar traits in separate lineages facing similar conditions. Plotopterids evolved a diving form resembling penguins despite their distant relationship.
Tonsala: An extinct genus of plotopterid seabirds known from Oligocene fossils in North America. It anchors the family’s fossil record on the eastern side of the Pacific.