Courtesy TmkeeseyMove over Lucy, there is a new hominid in town. Her name is Ardi. One could say Ardipithecus ramidus to be formal. She is a 4.4 million year old ancestor of ours and nearly a million years older than Lucy (Australopithecus afarensis). She is by far the most complete of all the older hominids. Researchers have recovered feet, a leg and pelvis, hands and lower arm, along with the majority of a skull and its teeth. As an added bonus, parts of nearly three dozen more specimens were recovered during the work in the Western Afar Rift of northeastern Ethiopia. This is the same region that gave us Lucy and some early Homo species.
Ardi and her kin walked upright, although their gait was debatably awkward. She retained an opposable toe which could still be used to grasp tree branches, but the remainder of the foot was built for the ground. Like later hominids, the teeth reveal a modern structure and lack enlarged canines. Her pelvis is a mosaic between chimps and Lucy. The Ilium developed short and broad more like a human, while the lower pelvis remains similar to a chimp. Ardi’s skull shows that her brain was still the size of a chimp, being smaller than Lucy’s. Its shape, however was more hominid and had begun evolve more advanced functions.
Unlike Lucy in her savannah habitat, Ardi roamed lush but temperate woodlands. More than 150,000 plant and animal fossils were recovered from the sites. Included are 20 new species of small mammals along with monkeys, antelope, elephants, and multitudes of birds. This was a much different environment than that of the savannah. Theories of the development of bipedalism on the open grasslands will be challenged now because of Ardi and her habitat.
This isn’t a recent find. The original excavations of the search teams started in 1992. But years of field work followed by more than a decade of lab time have really unearthed a mass of data about this time and place in history. 47 diverse researchers from all over the world have included excerpts of their findings about Ardi and her environment. The October 2009 special issue of the publication Science details the discovery and ongoing analysis of this latest find in the continuing quest to uncover the origins of man. With debate well underway, I’m positive we’ll all continue to learn more about our past.
more on Hominid evolution
Early human ancestors, called Australopithecines (AW-stroh-la-PITH-eh-scenes), had short legs. Scientists have long believed this was a hold-over from even earlier species which had lived in trees. But now biologist David Carrier of the University of Utah argues the short legs were used to help them fight.
Short legs give a body a lower center of gravity, and makes it harder to push over. Living apes with short legs, like gorillas, tend to be more aggressive, while long-legged apes, like gibbons, are more docile.
Of course, humans don’t have such short legs anymore. Herman Potzner of Washington University in St. Louis proposes later human species evolved long legs to save energy. His studies of various animals show that that longer a creature’s legs, the less energy they use. Around 2 million years ago, something happened in human evolution that made the fighting advantage of short legs less important than the energy savings of long legs.
The fossil including an entire skull, torso, shoulder blade and various limbs was discovered at Dikaka, some 400 kms northeast of the capital Addis Ababa near the Awash river in the Rift Valley.
"The finding is the most complete hominid skeleton ever found in the world," Zeresenay Alemseged, head of the Paleoanthropological Research Team, told a news conference. Reuters
The fossil has been named "Selam", which means peace in Ethiopia's official Amharic language.
"The Dikika girl stands as one of the major discoveries in the history of palaeoanthropology," research team leader Zeresenay Alemseged said, citing the remarkably well-preserved condition of the bones, the geological age and completeness of the specimen.Cosmos Magazine
The following is the abstract of the original article describing the baby, which was authored by Zeresenay Alemseged, Fred Spoor, William H. Kimbel, René Bobe, Denis Geraads, Denné Reed and Jonathan G. Wynn, and appeared in Nature on September 20, 2006.
"Understanding changes in ontogenetic development is central to the study of human evolution. With the exception of Neanderthals, the growth patterns of fossil hominins have not been studied comprehensively because the fossil record currently lacks specimens that document both cranial and postcranial development at young ontogenetic stages. Here we describe a well-preserved 3.3-million-year-old juvenile partial skeleton of Australopithecus afarensis discovered in the Dikika research area of Ethiopia. The skull of the approximately three-year-old presumed female shows that most features diagnostic of the species are evident even at this early stage of development. The find includes many previously unknown skeletal elements from the Pliocene hominin record, including a hyoid bone that has a typical African ape morphology. The foot and other evidence from the lower limb provide clear evidence for bipedal locomotion, but the gorilla-like scapula and long and curved manual phalanges raise new questions about the importance of arboreal behaviour in the A. afarensis locomotor repertoire."
Additional reading: BBC News