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Neonatal Shoulder Width Suggests A Semirotational, Oblique Birth Mechanism In Australopithecus Afarensis, Jeremy M. Desilva, Natalie M. Laudicina, Karen R. Rosenberg, Wenda R. Trevathan

Peer Reviewed Articles

Birth mechanics in early hominins are often reconstructed based on cephalopelvic proportions, with little attention paid to neonatal shoulders. Here, we find that neonatal biacromial breadth can be estimated from adult clavicular length (R² = 0.80) in primates. Using this relationship and clavicular length from adult Australopithecus afarensis, we estimate biacromial breadth in neonatal australopiths. Combined with neonatal head dimensions, we reconstruct birth in A. afarensis (A.L. 288-1 or Lucy) and find that the most likely mechanism of birth in this early hominin was a semi-rotational oblique birth in which the head engaged and passed through the inlet …