In Chapter 4 of the Revised Edition of Amsco’s The Living Environment: Biology (by Rick Hallman, © 2005), the author wrote that the oldest hominid fossils found so far, Ardipithecus ramidus, have been dated at 5.8 million years old. The fossils of these individuals, who lived in Ethiopia, show that the skull was balanced at the top of the skeleton for walking erect. Meanwhile, other animal fossils found nearby indicate that A. ramidus definitely lived in the forest. If careful studies of the A. ramidus bones show that it really did walk upright, the savanna hypothesis will be disproved.Well, it seems that we were on the right track. After more than 15 years of extensive scientific analysis of ancient hominid and other animal bones, fossil pollen, geological features, and radioactive dating, the scientists involved in the Ardipithecus research have presented evidence that may indeed overturn the “savannah hypothesis.” Just this month, the journal Science devoted its entire issue to articles about Ardipithecus, and not just any old collection of hominid bones. One very special Ardipithecus individual, nicknamed Ardi, is at the center of all the attention, and for several good reasons.
The Ardi specimen that is causing such a stir is important because she is 4.4 million years old―more than a million years older than the famous hominid fossil Lucy―and, like Lucy (also found in Ethiopia), she is a nearly complete skeleton. Hundreds of fossil bone fragments have been found from other Ardipithecus individuals, some much older than Ardi. But Ardi is the oldest most complete fossil hominid that has been found; she is represented by skull and teeth bones as well as hand and arm, foot and leg, and pelvic bones, thus giving a more complete picture of how she looked and moved. At about four feet tall, Ardi had a brain capacity not much different from that of a modern-day chimp; but she was already a bipedal animal. The analyses of fossilized pollen, as well as of other animal fossils, show that Ardi did in fact live in a wooded environment. This means that bipedalism arose while early hominids were still living in the forests; that is, our ancestors did not evolve bipedalism as an adaptive response to a more open savannah environment (like the one shown above).
Part of what makes Ardi so special is that the structure of her feet is not what the scientists would have predicted for such an early hominid, especially one that was already biped
al. Although the pelvis shows that she was already capable of walking upright as her main form of locomotion, her feet show that she could still grasp and climb in trees when needed, because there was a large gap between her big toe and the other toes. In addition, although this hominid is closer in time to the point at which the ancient hominids and chimps separated lineages, there is no evidence for the type of knuckle-walking that is seen today among the great apes. Other features of Ardi are less like those of modern chimps than was expected, too, such as her smaller upper canine teeth and a less protruded lower face. According to the prominent Harvard paleoanthropologist David Pilbeam, Ardi is “one of the most important discoveries for the study of human evolution.” And we will be sure to update the information about her in our next edition of The Living Environment: Biology.
2 comments:
What is the savannah hypothesis?
The savanna hypothesis suggests that early hominids developed a bipedal, ground-dwelling mode of locomotion when their formerly wooded environment went through a drying period and became a more open grasslands environment. Being bipedal would have enabled them to see predators across open spaces and would have freed their hands to carry food long distances.Carol
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