[Lucy's parturition, a way towards extinction?]

Objectives: To compare pelvic cavities in australopithecines, modern humans and non-hominid primates in order to discuss the obstetrical mechanisms in australopithecines

Material and methods: Bony pelves from fossil material (Australopithecus afarensis AL 288-1, Australopithecus africanus Sts14, Australopithecus Stw 431 and Mh2), 133 modern humans (82 adult females and 51 adult males) and 67 anthropoid primates (36 gorilla, 26 Pan troglodytes, 5 Pongo pygmaeus) were reconstructed and compared (shape and morphometric analysis) using 16 pelvimetric mesasurements.

Results: Pelves of australopithecines were characterized by lower anteroposterior (AP) and transverse (TRV) diameters in inlet pelvis than in other species. Index (AP/TRV) of pelvic inlet, midpelvis and pelvic outlet in the australopithecines were the lowest (<100) and the pelvic shape was platypelloid. A logarithmic factorial analysis showed that the pelvic morphology of australopithecines was different from humans and non-hominid primates but nearer the humans.

Discussion and conclusion: In contrast with apes where obstetrical mechanics seem to be easier, and because of platypelloidy, mechanism of birth in australopithecines was as difficult as in modern homo sapiens. Birth without cesarean was probably possible in an asynclitic TRV orientation.