Anatomical features - Essay Example

Bipedalism: An Anatomical Feature of Hominids Paleoanthropologists have long considered bipedalism to be an important factor in the analysis of human evolution. There is a consensus that bipedal walking, which freed the forelimbs for more dexterous tasks, such as tool making, is a defining characteristic of hominids. In this context, the status of bipedalism in two genera of hominids, Ardipithecus ramidus and Australopithecus afarensis, as seen from the anatomical examination of fossils, makes an interesting study.

The discovery of the fossil remains of Ardipithecus ranmidus at Aramis, in the Middle Awash region of Ethiopia, was announced in 2009. Radiometric analysis gives ‘Ardi’’s age as 4.4 million years, making her the oldest known hominid species to date. Ardi’s skeleton suggests a unique versatility and provides evidence of both biped and quadruped locomotion. The study of Ardi’s feet shows the markedly splayed big toe which facilitates the grasping of tree limbs, marking her as a quadruped in the trees.

However, the presence of a small bone inside a foot tendon, which is absent in both chimps and gorillas, increases the rigidity of the big toe. This feature, in combination with other toe modification, promotes biped locomotion on the ground. Similarly, the pelvis shows both the large flaring upper bones which facilitate steady bipedality, and the lower pelvis which accommodates the huge hind limb muscles used in climbing like an ape. Again, unlike the strictly rigid wrist bones of chimps and gorillas, which are geared towards hanging from trees and knuckle-walking on the ground, Ardi’s highly flexible wrists and finger joints indicate that Ardi walked on her palms on tree limbs – like primitive apes. (Shreeve. October 1, 2009.

National Geographic News). The most famous fossil remains of Australopithecus afarensis are the skeleton, "Lucy" found at Hadar, Ethopia, in 1974, the infant found at Dikika, Ethiopia, in 2006, and the 3.7 million years old footprints found in volcanic ash plus fossil bones found at Laetoli, Tanzania in 1978. The anatomical features in all these cases suggest that Australopithecus afarensis was capable of both bipedal and quadruped locomotion. Lucy’s long arm bones, and the ridge formed by the tendons attached to the humerus, indicate the strong chest and upper arm muscles required for tree climbing.

However, her short, broad pelvis supported her upright body and her angled-in thigh bones maintained her weight directly above her knees – both optimum features for walking. Likewise, while Lucy’s compact, weight-supporting feet were fashioned for walking, her long, curved toe bones are characteristic of tree-climbing apes. (Smithsonian Institution). In the case of the Dikika infant, the femur, tibia and foot present evidence of upright walking. However, the shoulder bone resembles that of the ape, and the long finger bones show the curvature of chimpanzees which assisted in tree-climbing.

In addition, the semi-circular canals of the inner ear resemble that of chimpanzee, adapted for maintaining balance necessary for arboreal life. (Max Planck Society. ScienceDaily 21 September 2006). The fossils of Australopithecus afarensis found in the vicinity indicate that the Laetoli footprints belong to this genus. The footprints show evidence of bipedalism. The big toes resemble humans and are aligned with the rest of the foot, unlike that of apes, whose big toes are divergent to aid tree climbing and grasping.

Additionally, the footprints exhibit the human-like gait of ‘heel strike’ followed by ‘toe-off,’ also indicative of bipedalism. (Smithsonian Institution). The information yielded by the anatomical features of the fossils in the case of Ardipithecus ranmidus and Australopithecus afarensis lead paleoanthropologists to infer that bipedalism was a locomotive characteristic of both genera. At the same time, strong evidence of quadruped locomotion is also present in the same fossils. It can thus be concluded that Ardipithecus ranmidus and Australopithecus afarensis were capable of walking upright on land and also equipped to live as tree-climbers.

The status of bipedality was obviously more established in the later Australopithecus afarensis. Being an effective biped, and simultaneously preserving its tree-climbing skills, could have given the two genera an effective advantage at survival, and later adaptive transition, in the evolution into bipedal hominids Works CitedShreeve, Jamie. October 1, 2009. National Geographic News. Oldest Skeleton of Human Ancestor Found. Accessed 22 November 2010 Max Planck Society. "Earliest Baby Girl Ever Discovered: Australopithecus Afarensis Child Sheds Light On Human Evolution.

" ScienceDaily 21 September 2006. 22 November 2010 Smithsonian National Museum of Natural History. What Does It Mean To Be Human? Australopithecus afarensis. Accessed 22 November 2010