Illustration of the great auk (Pinguinus impennis, here as Alca impennis), a species of flightless alcid that became extinct in the mid-19th century. It was the only modern species in the genus Pinguinus. It is not closely related to the birds now known as penguins, which were discovered later by Europeans and so named by sailors because of their physical resemblance to the great auk. Illustration by John Gerrard Keulemans from 'Extinct Birds: an attempt to unite in one volume a short account of those birds which have become extinct in historical times: that is, within the last six or seven hundred years: to which are added a few which still exist, but are on the verge of extinction' by Baron, Lionel Walter Rothschild, published in 1907.