The earliest unequivocal
fossils of pan-alcids are from the late
Eocene, some 35 mya. The
genus Miocepphus, (from the
Miocene, 15 mya) is the earliest known from associated specimens. Two Paleogene fossils were previously assigned to the Alcidae, but have since been removed to other clades:
Hydrotherikornis (late
Eocene) is a procellariiform and
Petralca (Late
Oligocene) is a loon. Miocene fossils have been found in both
California and
Maryland, but the greater diversity of fossils and tribes in the Pacific leads most scientists to conclude that it was there they first evolved, and it is in the Miocene Pacific that the first fossils of extant
genera are found. Early movement between the Pacific and the Atlantic probably happened to the south (since there was no northern opening to the Atlantic), later movements across the Arctic Ocean. The flightless clade
Mancallinae was present in the eastern and western Pacific Ocean and became extinct in the Late
Pleistocene. ==References==