Developmental maturity categories of Langer [21] and mineralization of first molar M1 and other permanent teeth in newborn terrestrial mammals compared to the early whale Maiacetus inuus.

Living whales are not included because none have deciduous teeth and many have few or no teeth. Because early whales evolved from artiodactyls [3], Ovis, Dama, Hexaprotodon, and Giraffa are better analogs than primates.1Presence of mineralization of the crown of M1 in the fetal skull of Maiacetus inuus indicates precocial development and the probability that newborns were open-eyed, hairy and nidifugous.