page_title: Australopithecus sediba
section_title: Birth
hierarchical_section_title: Australopithecus sediba / Palaeobiology / Birth
caption_attribution_description: English: Ellipse representing a neonatal A. sediba head at the pelvic. A. inlet, frontal view B. inlet, superior view C. midplane, superior view. Reconstructed pelvis is shown with the MH1 ischium. Notice that the modeled A. sediba neonatal cranium can descend into the midplane without bony constraints, unlike the condition typically found in modern humans.
context_page_description: Australopithecus sediba is an extinct species of australopithecine recovered from Malapa Cave, Cradle of Humankind, South Africa. It is known from a partial juvenile skeleton, the holotype MH1, and a partial adult female skeleton, the paratype MH2. They date to about 1.98 million years ago in the Early Pleistocene, and coexisted with Paranthropus robustus and Homo ergaster/H. erectus. Malapa is interpreted as having been a natural death trap, the base of a long vertical shaft which creatures could accidentally fall into. A. sediba was initially described as being a potential human ancestor, and perhaps the progenitor of Homo, but this is contested and it could also represent a late-surviving population or sister species of A. africanus which had earlier inhabited the area.
  MH1 has a brain volume of about 420–440 cc, similar to other australopithecines. The face of MH1 is strikingly similar to Homo instead of other australopithecines, with a less pronounced brow ridge, cheek bones, and prognathism, and there is evidence of a slight chin. However, such characteristics could be due to juvenility and lost with maturity. The teeth are quite small for an australopithecine.
context_section_description: The pelvic inlet for a female A. sediba is estimated to have been 80.8 mm × 112.4 mm (3.18 in × 4.43 in) long x broad (sagittal x transverse), and since the neonate head size is estimated to have been 89.2 mm (3.51 in) at longest, the neonate probably entered the pelvic inlet transversely orientated similar to other hominins. The midplane of the pelvic inlet is constricted to a minimum of 96.9 mm (3.81 in), so the neonate may not have needed to be rotated while being birthed. Pelvic inlet dimensions were calculated using a composite reconstruction involving the juvenile male ischium; likewise, the birth canal was possibly actually larger than calculated. The shoulders are estimated to have been 74.3 mm (2.93 in) across, so they would not have obstructed birth more than the head would have. Therefore, the neonate would have occupied, at the point of most constriction, about 92.1% of the birth canal, allowing sufficient room for a completely non-rotatonal birth as is exhibited in non-human apes and possibly other australopithecines (though a semi-rotational birth is also proposed). Though it is possible to pass without any rotation, the midplane expands anteroposteriorly (from front to back), and there would have been more space for the neonate if it rotated so that the longest length of the head lined up with this expansion.
  Modern humans, in comparison, have a much more labourious and complex birth requiring full rotation of the neonate, as the large brain and thus head size, as well as the rigid shoulders, of the human neonate make it much more difficult to fit through the birth canal. Using an estimate of 145.8–180.4 cc for A. sediba neonate brain size, neonate head size would have been 73 mm × 89 mm (2.9 in × 3.5 in), similar to a chimp neonate.
caption: Reconstruction of an A. sediba neonate entering the pelvic inlet (A and B) and the midplane without rotation (C)
exif: {}