Sites: Ethiopia
There are now more than 30 fossils making up at least nine individuals, dated between 4.3 and 4.5 million years old. ARA-VP-1/129: 4.4 million years; discovered between 1992 and 1993 in Aramis, Ethiopia. This partial lower jaw from a child is one of several fossils known for this species. It shows a very primitive tooth structure relative to later hominid species. The fossils include teeth, an adult mandible, pieces of skull, several arm bones, hand and foot bones and a piece of clavicle. In 1994 Tim White and colleagues found by far the most informative fossil – a partial skeleton of ARA-VP-6/500. A total of 90 fragments accumulated to about 50% of a total skeleton. Even though it was found crushed and fragmented, the years of work and computer imaging have now allowed researchers to interpret this 4.4- million-year-old individual nicknamed “Ardi”. Ardi has been sexed as female and contains several key portions, including a skull, a pelvis, and almost complete hands and feet The foramen magnum and leg fragments initially indicate this species was bipedal. Between 1997 and 2000, Yohannes Haile-Selassie and colleagues recovered another 11 hominid specimens comprising five individuals who lived between five and six million years ago. They initialy placed them in the pre-human subspecies, Ardipithecus ramidus, but discovery of another six additional teeth (upper canine, upper and lower premolars and upper molars from different individuals), had the team reclassify all specimens dating between 5.54 and 5.77 million years old into their own species, Ardipithecus kadabba. In 2005, excavators working in Ethiopia found remains of at least nine more hominids dating to between 4.5 million and 4.3 million years old. The fossils found at As Duma in northern Ethiopia, are mostly fragments of teeth and jaws, but also include pieces of hands and feet. One pedal phalanx confirmed that the hominid probably walked upright like modern humans. Most of the fossils finds of this species show a mix of both primitive (ape-like) and advanced (Australopithecene-like) traits.
Cranial architecture: Foramen magnum anteriorly placed. Flattened cranial base Dentition: Most of the dentition is more primitive or ape-like, but similarities with later hominids exist. It is thus likely that this hominid occupied a different dietary niche than either the apes or later hominids. Postcranial: Humerus differ from quadrapeds and suggests that A. ramidus was bipedal. The angle of the femora appears more similar to bipedal hominids than chimpanzees. The mandible and partial postcranial skeleton of a single individual found in 1994 are still being analysed and should clear up wether or not this was truly a bipedal hominid. The anteriorly placed foramen magnum indicates that the skull rested atop the vertebral column, and, if not yet fully bipedal, it had at least some adaptations toward full bipedalism. Environment: Woodland habitat In the early Pliocene, this area would have had forests, swamps, springs and streams, and experienced seasonal droughts. The pedal phalanx suggesting that A. ramidus walked upright, poses a problem for current theories on the origin of hominid bipedalism. If Ardipithecus lived in shady forests and not savannah, the more efficient locomotion permitted by bipedalism would not be of any advantage. Length and weight:
Ancestor: Descendants: General: A. ramidus is accepted as one of the earliest and most primitive hominids. The species is characterised by more primitive (apelike) characters than those seen in later hominids. Tim White, Gen Suwa and Berhane Asfaw discovered the first A. ramidus fossils in the Middle Awash region of Ethiopia. Orrorin tugenensis and Sahelanthropus tchadensis are slightly older than Ardipithecus. It is suggested that all three these species might belong in one group, namely Ardipithecus. Because of the number of traits shared by African great apes (genus Pan and genus Gorilla), some researchers feel that it belongs on the chimpanzee and not human branch. At present, most consider it to be a proto-human. References:
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