The earliest unequivocal fossils of auks are from the late Eocene, some 35 mya. The genus "Miocepphus", (from the Miocene, 15 mya) is the earliest known from good specimens. Two very fragmentary fossils are often assigned to the Alcidae, although this may not be correct: "Hydrotherikornis" (late Eocene) and "Petralca" (Late Oligocene). Most extant genera are known to exist since the Late Miocene or Early Pliocene (c. 5 mya). 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 subfamily Mancallinae, which was apparently restricted to the Pacific coast of southern North America and became extinct in the Early Pleistocene, is sometimes includes in the family Alcidae under some definitions. One species, "Miomancalla howardae", is the largest charadriiform of all time.