Table 4. 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.
| Species | Mineralization of the permanent dentition at birth | Reference |
| Category I. Altricial: eyes closed, naked, nidicolous or ‘nest-dwelling’ | ||
| Gray short-tail opossum, Monodelphis domestica | None | [33] |
| Brown bear, Ursus arctos | None | [22] |
| Indian mongoose, Herpestes auropunctatus | None | [34] |
| Ferret, Mustela putorious | None | [35] |
| Domestic dog, Canis familiaris | Trace | [36] |
| Category II. Precocial: eyes open, haired, nidicolous or ‘nest-dwelling’ | ||
| Domestic pig, Sus scrofa | None | [37] |
| Miniature pig, Sus scrofa | M1 cusp tips beginning to mineralize | [38] |
| Collared peccary, Tayassu tajacu | M1 cusp tips formed | [39] |
| Category III. Precocial: eyes open, haired, transported (largely primates) | ||
| Human, Homo sapiens | M1 cusp tips beginning to mineralize | [40] |
| Great apes, Pan, Gorilla, and Pongo spp. | M1 cusp tips beginning to mineralize | [40] |
| Gibbon, Hylobates sp. | M1 cusp tips beginning to mineralize | [40] |
| Rhesus macaque, Macaca mulaltta | M1 cusp tips formed | [41] |
| Mongoose lemur, Eulemur mongoz | M1 cusp tips formed | [42] |
| Coquerel's sifaka, Propithecus verreauxi | M1 crown almost complete, M2 near coalescence, M3 trace | [42] |
| Tarsier, Tarsius bancanus | M1 ‘well differentiated’ (some deciduous teeth resorbed in utero) | [43] |
| Category IV. Precocial: eyes open, haired, nidifugous or ‘nest-fleeing’ | ||
| American tapir, Tapirus cf. T. bairdii | M1 anterior cusps connected | [44] |
| Domestic sheep, Ovis aries | M1 cusps connected; crown one-quarter formed | [45] |
| Maiacetus inuus 1 | M1 crown one-half formed | this study |
| Fallow deer, Dama dama | M1 crown one-half formed | [46] |
| Pygmy hippo, Hexaprotodon liberensis | M1? (many deciduous teeth erupted at birth; large M1 crypt) | [27] |
| Giraffe, Giraffa camelopardalis | M1 crown complete (all deciduous teeth erupted at birth) | [47] |
| Fur seal, Callorhinus ursinus | M1-2 crowns complete (deciduous teeth shed in utero) | [48] |
| Guinea pig, Cavia porcellus | All permanent teeth erupted; roots incomplete | [23] |
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.
1
Presence 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.