Concept: Donald Johanson
Sexual dimorphism in body size is often used as a correlate of social and reproductive behavior in Australopithecus afarensis. In addition to a number of isolated specimens, the sample for this species includes two small associated skeletons (A.L. 288-1 or “Lucy” and A.L. 128/129) and a geologically contemporaneous death assemblage of several larger individuals (A.L. 333). These have driven both perceptions and quantitative analyses concluding that Au. afarensis was markedly dimorphic. The Template Method enables simultaneous evaluation of multiple skeletal sites, thereby greatly expanding sample size, and reveals that A. afarensis dimorphism was similar to that of modern humans. A new very large partial skeleton (KSD-VP-1/1 or “Kadanuumuu”) can now also be used, like Lucy, as a template specimen. In addition, the recently developed Geometric Mean Method has been used to argue that Au. afarensis was equally or even more dimorphic than gorillas. However, in its previous application Lucy and A.L. 128/129 accounted for 10 of 11 estimates of female size. Here we directly compare the two methods and demonstrate that including multiple measurements from the same partial skeleton that falls at the margin of the species size range dramatically inflates dimorphism estimates. Prevention of the dominance of a single specimen’s contribution to calculations of multiple dimorphism estimates confirms that Au. afarensis was only moderately dimorphic.
The Australopithecus afarensis partial skeleton A.L. 288-1, popularly known as “Lucy” is associated with nine vertebrae. The vertebrae were given provisional level assignments to locations within the vertebral column by their discoverers and later workers. The continuity of the thoracic series differs in these assessments, which has implications for functional interpretations and comparative studies with other fossil hominins. Johanson and colleagues described one vertebral element (A.L. 288-1am) as uniquely worn amongst the A.L. 288-1 fossil assemblage, a condition unobservable on casts of the fossils. Here, we reassess the species attribution and serial position of this vertebral fragment and other vertebrae in the A.L. 288-1 series. When compared to the other vertebrae, A.L. 288-1am falls well below the expected size within a given spinal column. Furthermore, we demonstrate this vertebra exhibits non-metric characters absent in hominoids but common in large-bodied papionins. Quantitative analyses situate this vertebra within the genus Theropithecus, which today is solely represented by the gelada baboon but was the most abundant cercopithecoid in the KH-1s deposit at Hadar where Lucy was discovered. Our additional analyses confirm that the remainder of the A.L. 288-1 vertebral material belongs to A. afarensis, and we provide new level assignments for some of the other vertebrae, resulting in a continuous articular series of thoracic vertebrae, from T6 to T11. This work does not refute previous work on Lucy or its importance for human evolution, but rather highlights the importance of studying original fossils, as well as the efficacy of the scientific method.
Following a global morphological and micro-CT scan examination of the original and cast of the skeleton of Australopithecus afarensis AL 288 (‘Lucy’), Kappelman et al. have recently proposed a diagnosis of a fall from a significant height (a tree) as a cause of her death. According to topographical data from the discovery site, complete re-examination of a high-quality resin cast of the whole skeleton and forensic experience, we propose that the physical process of a vertical deceleration cannot be the only cause for her observed injuries. Two different factors were involved: rolling and multiple impacts in the context of a mudslide and an animal attack with bite marks, multi-focal fractures and violent movement of the body. It is important to consider a differential diagnosis of the observed fossil lesions because environmental factors should not be excluded in this ancient archaeological context as with any modern forensic anthropological case.
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.
The estimated lower limb length (0.761-0.793 m) of the partial skeleton of Australopithecus afarensis from Woranso-Mille (KSD-VP-1/1) is outside the previously known range for Australopithecus and within the range of modern humans. The lower limb length of KSD-VP-1/1 is particularly intriguing when juxtaposed against the lower limb length estimate of the other partial skeleton of A. afarensis, AL 288-1 (0.525 m). A sample of 36 children (age, >7 years, trochanteric height = 0.56-0.765 m) and 16 adults (trochanteric height = 0.77-1.00 m) walked at their self-selected slow, preferred, and fast walking velocities, while their oxygen consumption was monitored. Lower limb length and velocity were correlated with slow (P < 0.001, r(2) = 0.44), preferred (P < 0.001, r(2) = 0.55), and fast (P < 0.001, r(2) = 0.69) walking velocity. The relationship between optimal velocity and lower limb length was also determined and lower limb length explained 47% of the variability in optimal velocity. The velocity profile for KSD-VP-1/1 (slow = 0.73-0.75 m/s, preferred = 1.08-1.11 m/s, and fast = 1.48-1.54 m/s) is 36-44% higher than that of AL 288-1 (slow = 0.53 m/s, preferred = 0.78 m/s, and fast = 1.07 m/s). The optimal velocity for AL 288-1 is 1.04 m/s, whereas that for KSD-VP-1/1 is 1.29-1.33 m/s. This degree of lower limb length dimorphism suggests that members of a group would have had to compromise their preferences to walk together or to split into subgroups to walk at their optimal velocity. Am J Phys Anthropol, 2012. © 2012 Wiley Periodicals, Inc.