Daegling David J, Carlson Kristian J, Tafforeau Paul, de Ruiter Darryl J, Berger Lee R
Department of Anthropology, University of Florida, Gainesville, FL 32611-7305, USA.
Evolutionary Studies Institute, University of the Witwatersrand, Private Bag 3, Johannesburg 2050, South Africa; Department of Anthropology, Indiana University, Bloomington, IN 47405, USA; School of Geosciences, University of the Witwatersrand, Private Bag 3, Johannesburg 2050, South Africa; Department of Cell & Neurobiology, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA.
J Hum Evol. 2016 Nov;100:73-86. doi: 10.1016/j.jhevol.2016.08.006.
Fossils attributed to Australopithecus sediba are described as having phylogenetic affinities with early Homo to the exclusion of other South African australopiths. With respect to functional anatomy of mastication, one implication of this hypothesis is that A. sediba mandibles should exhibit absolutely and relatively reduced stiffness and strength in comparison to Australopithecus africanus and Paranthropus robustus jaws. Examination of cortical bone distribution in the MH 1 and MH 2 mandibles of A. sediba (evaluated against samples of Pan, early and modern Homo as well as A. africanus and P. robustus) indicate that the A. sediba mandibular corpus was geometrically similar to other South African australopiths. In particular, enhanced torsional rigidity is characteristic of all South African australopiths including A. sediba. These findings are consistent with a hypothesis that masticatory mechanics may have been similar to other australopiths (and distinct from exemplars of early Homo), and as such suggest that A. sediba's mandibles were functionally suited to consume hard and tough objects. Recent mechanical modeling of the A. sediba cranium, however, has been interpreted as indicating that this species was relatively poorly adapted to produce large bite forces and likely experienced relatively modest strains in its facial skeleton. This paradox - that the cranium signals a departure from the australopith morphotype whereas the mandibles conform to a hypodigm of australopith grade - can be resolved, in part, if it is acknowledged that mechanical performance variables offer imperfect insight into what constitutes feeding adaptations.
被归类为南方古猿源泉种的化石被描述为与早期人类具有系统发育亲缘关系，而排除了其他南非南方古猿。关于咀嚼的功能解剖学，这一假设的一个含义是，与非洲南方古猿和粗壮傍人颌骨相比，南方古猿源泉种的下颌骨在绝对和相对刚度及强度上应有所降低。对南方古猿源泉种的MH 1和MH 2下颌骨的皮质骨分布进行检查（与黑猩猩、早期和现代人类以及非洲南方古猿和粗壮傍人的样本进行对比评估）表明，南方古猿源泉种的下颌体在几何形状上与其他南非南方古猿相似。特别是，包括南方古猿源泉种在内的所有南非南方古猿都具有增强的抗扭刚度。这些发现与这样一种假设一致，即咀嚼力学可能与其他南方古猿相似（且与早期人类的范例不同），因此表明南方古猿源泉种的下颌骨在功能上适合咀嚼坚硬和坚韧的食物。然而，最近对南方古猿源泉种颅骨的力学建模被解释为表明该物种相对不太适应产生较大咬合力，并且其面部骨骼可能承受相对较小的应变。这个悖论——颅骨表明与南方古猿形态类型不同，而下颌骨符合南方古猿等级的模式——如果承认力学性能变量对构成进食适应性的理解并不完美，那么可以部分得到解决。
