The great auk belonged to the family Alcidae, alongside puffins, guillemots and razorbills. It is the only member of that family known to have lost flight in modern times. Its wings were short and stiff, well suited to propulsion underwater but useless in the air, and its genus name Pinguinus preserves the older use of the word.
The resemblance to true penguins is convergence. Both lineages solved the same problem of pursuing fish underwater in cold seas, and both arrived at a torpedo-shaped body, dense bones, counter-shaded plumage and wings reworked into flippers. They are separated by the whole width of the bird family tree and by hemispheres.
Flightlessness made the great auk easy to kill at its breeding colonies, which were few and crowded. Harvesting for meat, oil and down was compounded in the final decades by collectors paying well for skins and eggs. The last confirmed birds were taken on Eldey, off Iceland, on 3 June 1844.