The human fossil record is one of the most complete for any mammal. A basal ancestral species, Australopithecus afarensis, exhibits a well-preserved postcranium that permits reconstruction of ...important events in the evolution of our locomotor skeleton. When compared to those of living apes and humans, it provides insights into the origin and design of the modern human frame. Evolutionary aspects of the human hip and thigh are reviewed, including the unusual corticotrabecular structure of the human proximal femur, and our markedly elongated lower limb. It is postulated that the latter may be more related to birthing capacity than to locomotion.
The origin of Australopithecus, the genus widely interpreted as ancestral to Homo, is a central problem in human evolutionary studies. Australopithecus species differ markedly from extant African ...apes and candidate ancestral hominids such as Ardipithecus, Orrorin and Sahelanthropus. The earliest described Australopithecus species is Au. anamensis, the probable chronospecies ancestor of Au. afarensis. Here we describe newly discovered fossils from the Middle Awash study area that extend the known Au. anamensis range into northeastern Ethiopia. The new fossils are from chronometrically controlled stratigraphic sequences and date to about 4.1-4.2 million years ago. They include diagnostic craniodental remains, the largest hominid canine yet recovered, and the earliest Australopithecus femur. These new fossils are sampled from a woodland context. Temporal and anatomical intermediacy between Ar. ramidus and Au. afarensis suggest a relatively rapid shift from Ardipithecus to Australopithecus in this region of Africa, involving either replacement or accelerated phyletic evolution.
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.
During the Pleistocene Peopling of North America, the use of stone outcrops for forager gatherings would have provided Clovis colonizing hunter-gatherers with several advantages beyond that of ...toolstone procurement. Stone outcrops would have been predictable and immovable places on an emerging map of a landscape for a thinly scattered colonizing population needing to find one another, as well as ideal teaching locales where novice flintknappers could learn to make the complex Clovis fluted projectile point without worrying about running out of, or transporting, raw material. For these reasons, several researchers have suggested that stone outcrops were 'hubs' of regional Clovis activity where Clovis people not only made tools, but also assembled in large groups at outcrop-related base camps. Once there, they exchanged information and mates, feasted, lived and explored. Here the authors test, using microwear analysis of stone tools, the hypothesis that the Welling site, located within the Upper Mercer chert source area, was an outcrop-related base camp. Their results - suggesting a variety of stone tool functions including dry- and fresh-hide scraping, hide cutting, meat butchering, sawing and scraping bone/antler, sawing and scraping wood, and plant scraping - were consistent with the idea that Welling represents an outcrop-related basecamp in which Clovis foragers assembled, carried out a variety of activities, and regularly travelled to and from the site. These results, when considered in conjunction with recent morphometric analysis of Clovis fluted projectile points, suggest that Welling was indeed a 'hub' of Clovis regional activity in Northeast Ohio, and permit us to propose a scenario for how the region was colonized during the terminal Pleistocene.
Upright walking absent a bent-hip-bent-knee gait requires lumbar lordosis, a ubiquitous feature in all hominids for which it can be observed. Its first appearance is therefore a central problem in ...human evolution. Atelids, which use the tail during suspension, exhibit demonstrable lordosis and can achieve full extension of their hind limbs during terrestrial upright stance. Although obviously homoplastic with hominids, the pelvic mechanisms facilitating lordosis appear largely similar in both taxa with respect to abbreviation of upper iliac height coupled with broad sacral alae. Both provide spatial separation of the most caudal lumbar(s) from the iliac blades. A broad sacrum is therefore a likely facet of earliest hominid bipedality. All tailed monkeys have broad alae. By contrast all extant apes have very narrow sacra, which promote "trapping" of their most caudal lumbars to achieve lower trunk rigidity during suspension. The alae in the tailless proconsul Ekembo nyanzae appear to have been quite broad, a character state that may have been primitive in Miocene hominoids not yet adapted to suspension and, by extension, exaptive for earliest bipedality in the hominid/panid last common ancestor. This hypothesis receives strong support from other anatomical systems preserved in Ardipithecus ramidus.
One specimen of Ardipithecus ramidus, ARA-VP-6/500, is the earliest and also among the most complete fossil hominids ever recovered. Although it took more than a decade to extract, prepare, and ...analyze (along with a number of other less-complete specimens), the thoroughness of its recovery and preparation has yielded surprising revelations about its environment as well as new knowledge about the divergence of our earliest human ancestors from the last common ancestor they shared with chimpanzees. Decades of groundbreaking discoveries in developmental biology have also transformed our understanding of the evolutionary process itself, especially the need to view the significance of adult anatomical structures holistically. Today, no such structure can be reasonably understood without direct reference to its likely mode of morphogenesis. The twenty-first-century convergence of these two special sources of information requires a radical revision of how our early hominid forebears set the stage for our own subsequent evolution. Although we usually attribute our complex social structure to our massive brain, current evidence suggests that the reverse might have been true almost as far back as the original emergence of our clade.
We assigned Ardipithecus to the Hominidae based on numerous dental, cranial, and postcranial characters. Sarmiento argues that these characters are not exclusive to hominids, contending that ...Ardipithecus is too old to be cladistically hominid. His alternative phylogeny, however, is unlikely because it requires tortuous, nonparsimonious evolutionary pathways.
Seeman, Morris, and Summers misrepresent or misunderstand the arguments we have made, as well as their own previous work. Here, we correct these inaccuracies. We also reiterate our support for ...hypothesis-driven and evidence-based research.
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