Early Bipedal Hominids Essay, Research Paper
Bipedal Locomotion in Early Hominids
Until recently, the oldest fossil species to provide evidence for bipedalism was Australopithecus afarensis, of which the best example of is the 3.2 million year old skeleton called Lucy found in Hadar, Ethiopia. According to article 19: Sunset at the Savanna, in 1995 Meave Leakey of the national Museums of Kenya and her colleagues made public the discovery of and older hominid species Australopithecus anamensis (getting its name from the Turkana word for lake “anam” having been found near lake Turkana and the site of another ancient lake). Leakey’s team found a tibia from this creature that is quite human like and emphatically bipedal, “in size and practically all details of the knee and ankle joints… (it) resembles the one from the fully bipedal A. afarensis”. The site where the fossils were found was dated to 4.2-3.9 million years ago; making 4.2mya the oldest date at which we can say that bipedalism has been proven to have emerged. There are also many other more recent fossils which have evidenceof bipedalism: Australopithecus africanus, Australopithecus robustus, and maybe another recently found fossil classified Ardipithecus ramidus
There are several aspects of skeletal anatomy that indicate bipedalism. We learned in lab last week that the pelvis has features that indicate the mode of locomotion. A bipedal creature will have an ilium that is short and wide. The leg bones will give clues too. A bipedal creature has knees that point more directly forward than a quadrapedal creature (this is why apes look very awkward when they walk bipedally, their legs kick out to the side when they step forward.) Another skeletal feature that indicates bipedalism is a special design of the anklebones so that they would be able to take the weight of a bipedal stride. The knee bone of a bipedal hominid has a special feature too. It has extra spongy bone tissue that acts as a shock absorber when walking. One feature mentioned in article 20 is a oval hollow at the bottom of the humerus where the humerus and the ulna lock in place. This is an adaptation to knuckle walking and is not present in bipedal hominids.
Many theories have been made about what type of paleoecology or paleoecological changes were the niche for bipedalism. It must have been a strong force since bipedaliam is generally slower and more awkward than quadrapedal locomotion. It also puts the animal at a greater risk of injury, according to Owen Lovejoy of Kent State. The current most widely accepted theory is that there was a continent wide drying up of Africa starting around 5mya. This caused shrinkage of the large forests to scattered patches and an increase in the size and amount of savanna grassland. The savanna hypothesis states that these changes forced our ancestors to adapt from living solely in the jungle to spending some time in the savanna where bipedalism would make them better suited through such ways as providing them greater protection from the sun by putting less surface area of their bodies directly under it. Walking bipedally would be an efficient manner of locomotion through the arid and somewhat barren (compared to the jungles) savanna grasslands between the sparse resource richer forests. Standing upright on the hind legs would have raised out ancestors heads above the tall savanna grasses so that they could see where they were going, whatever they might be looking for or what predators might have been looking for them. Some anthropologists theorize that bipedal locomotion was reinforced by the fact that the freed arms could be used for such tasks as carrying large amounts of food to feed their young and mate(s). Later, as hominids became more intelligent, the arms could be used to carry weapons for defense against predators and for hunting.