Ardipithecus

Taxobox
name = "Ardipithecus"
fossil_range = Pliocene


image_caption = "Ardipithecus kadabba" fossils
regnum = Animalia
phylum = Chordata
classis = Mammalia
ordo = Primates
familia = Hominidae
subfamilia = Homininae
tribus = Hominini
genus = "Ardipithecus"
genus_authority = White et al., 1995
subdivision_ranks = Species
subdivision = †"Ardipithecus kadabba"
†"Ardipithecus ramidus"

"Ardipithecus" is a very early hominin genus (subfamily Homininae) which lived about 4.4 million years ago during the early Pliocene.

Because this genus shares several traits with the African great ape genera (genus "Pan" and genus "Gorilla"), it is considered by some to be on the chimpanzee rather than human branch, but most consider it a proto-human because of a likeness in teeth with "Australopithecus".

Species

Two species have been described, "Ardipithecus ramidus" and "Ardipithecus kadabba", which was initially described as a subspecies of "A. ramidus", but on the basis of teeth recently discovered in Ethiopia has been raised to species rank. Remains from both species have been found in the Middle Awash.

Ardipithecus ramidus

"A. ramidus" was named in September 1994. The first fossil find was dated to 4.4 million years ago based on its interval between two volcanic strata: the basal Gaala Tuff Complex (GATC) and the Daam Aatu Basaltic Tuff (DABT). Subsequent fossil discoveries by Yohannes Haile-Selassie and Giday WoldeGabriel—if identified as "A. ramidus"—would push the date back as far as 5.8 million years ago. [cite web | author = Perlman, David | date = 2001-07-12 | title = Fossils From Ethiopia May Be Earliest Human Ancestor | work = San Francisco Chronicle, as reported in National Geographic News | url = http://news.nationalgeographic.com/news/2001/07/0712_ethiopianbones.html]

In 1992-1993 a research team headed by Dr Timothy White discovered the first "A. ramidus" fossils—seventeen fragments including skull, mandible, teeth and arm bones—from the Afar Depression in the Middle Awash river valley of Ethiopia. More fragments were recovered in 1994, amounting to 45 percent of the total skeleton. Features of the foramen magnum and leg fragments are indicative of bipedalism. [cite web | title = Ardipithecus ramidus | url = http://www.archaeologyinfo.com/ardipithecusramidus.htm | accessdate = 2008-01-18] [cite web | url = http://www.talkorigins.org/faqs/homs/species.html | title = Hominid Species | accessdate = 2008-01-18]

Ardipithecus kadabba

"A. kadabba" is dated to have lived between 5.8 million to 5.2 million years ago. The canine teeth show primitive features, shared with "Sahelanthropus" and "Orrorin", that distinguish them from those of more recent hominins. It has been suggested that "A. kadabba" is the most recent common ancestor of "Homo" and "Pan". Anthropologists Yohannes Haile-Selassie, Gen Suwa, and Tim D. White published an article suggesting that the presence of a "canine cutting complex" indicates a need for relocation in hominid evolutionary history. [cite journal |last=Haile-Selassie |first=Yohannes |authorlink= |coauthors=Suwa, Gen; White, Tim D. |year=2004 |month= |title=Late Miocene Teeth from Middle Awash, Ethiopia, and Early Hominid Dental Evolution |journal=Science |volume=303 |issue=5663 |pages=1503–1505 |doi=10.1126/science.1092978 |url= |quote=|pmid=15001775 ] Since "A. ramidus" is lacking the canine cutting complex, the authors argue, it is reasonable to infer the canine cutting complex, which is present in modern day chimpanzees, is a primitive trait which was lost during hominin evolution. The specific name comes from the Afar word for "basal family ancestor".cite book| last = Ellis| first = Richard| authorlink = Richard Ellis (biologist) | title = No Turning Back: The Life and Death of Animal Species| publisher = Harper Perennial | date = 2004| location = New York| pages = 92| isbn =0-06-055804-0 ]

Lifestyle

On the basis of bone sizes, "Ardipithecus" species are believed to have been about the size of a modern chimpanzee.

The toe structure of "A. ramidus" suggests that the creature walked upright, and this poses problems for current theories of the origins of hominid bipedalism: "Ardipithecus" is believed to have lived in shady forests rather than on the savannah, where the more energy efficient locomotion permitted by bipedalism would have been an advantage.

References

External links

* [http://news.bbc.co.uk/2/hi/science/nature/4187991.stm BBC News: Amazing hominid haul in Ethiopia]
* [http://www.nytimes.com/2006/05/18/science/18evolve.html?pagewanted=2&_r=1 NY Times: Two Splits Between Human and Chimp Lines Suggested]
* [http://www.mnsu.edu/emuseum/biology/humanevolution/ramidus.htm Minnesota State University]
* [http://www.archaeologyinfo.com/ardipithecusramidus.htm Archaeology info]