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Ardipithecus
Fossil range: Pliocene
Ardipithecus ramidus specimen, nicknamed Ardi
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Family: Hominidae
Subfamily: Homininae
Tribe: Hominini
Genus: Ardipithecus
White et al., 1995
Species

Ardipithecus kadabba
Ardipithecus ramidus

Ardipithecus is a very early hominin genus. Two species are described in the literature: A. ramidus, which lived about 4.4 million years ago[1] during the early Pliocene, and A. kadabba, dated to approximately 5.6 million years ago (late Miocene).[2]

Contents

Ardipithecus ramidus

Map showing discovery location

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). The name Ardipithecus ramidus stems mostly from the Afar language, in which Ardi means "ground/floor" and ramid means "root". The pithecus portion of the name is from the Greek word for "ape".[3] Its distinguishing characteristics are bipedalism incorporating an arboreal grasping hallux or big toe, reduced canine teeth and a smaller brain size comparable to that of the modern chimpanzee.

In 1992–1993 a research team headed by Tim 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% of the total skeleton. This fossil was originally described as a species of Australopithecus, but White and his colleagues later published a note in the same journal renaming the fossil under a new genus, Ardipithecus. Between 1999 and 2003, a multidisciplinary team led by Sileshi Semaw discovered bones and teeth of nine A. ramidus individuals at As Duma in the Gona Western Margin of Ethiopia's Afar Region.[4] The fossils were dated to between 4.32 and 4.51 million years old.[5]

Ardipithecus ramidus had a small brain, measuring between 300 and 350 cm3. This is about the same size as a modern bonobo or female common chimpanzee brain, but much smaller than the brain of australopithecines like Lucy (~400 to 550 cm3) and roughly 20% the size of the modern Homo sapiens brain. Like common chimpanzees, A. ramidus was much more prognathic than modern humans.[6]

The teeth of A. ramidus lacked the specialization of other apes, and suggest that it was a generalized omnivore and frugivore (fruit eater) with a diet that did not depend heavily on fibrous plants, ripe fruit or hard or abrasive food. The size of the upper canine tooth in A. ramidus males was not distinctly different than that of females. Their upper canines were less sharp than those of modern common chimpanzees in part because of this decreased upper canine size, as larger upper canines can be honed through wear against teeth in the lower mouth. The features of upper canine in A. ramidus contrast with the sexual dimorphism observed in common chimpanzees, where males have significantly larger and sharper upper canine teeth than females.[7]

The less pronounced nature of upper canine teeth in A. ramidus has been used to infer aspects of the social behavior of the species and more ancestral hominids. In particular, it has been used to suggest that the last common ancestor of hominids and African apes was characterized by relatively little aggression between males and between groups. This is markedly different from social patterns in common chimpanzees, among which intermale and intergroup aggression are typically high. Researchers in a 2009 study said that this condition "compromises the living chimpanzee as a behavioral model for the ancestral hominid condition."[7]

A. ramidus existed more recently than the most recent common ancestor of humans and chimpanzees, and thus is not fully representative of that common ancestor. Nevertheless, it is in some ways unlike chimpanzees, suggesting that the common ancestor differs from the modern chimpanzee. After the chimpanzee and human lineages diverged, both underwent substantial evolutionary change. Chimp feet are specialized for grasping trees; A. ramidus feet are better suited for walking. The canine teeth of A. ramidus are smaller, and equal in size between males and females, which suggests reduced male-to-male conflict, increased pair-bonding, and increased parental investment. "Thus, fundamental reproductive and social behavioral changes probably occurred in hominids long before they had enlarged brains and began to use stone tools," the research team concluded.[2]

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Ardi

On October 1, 2009, paleontologists formally announced the discovery of the relatively complete A. ramidus fossil skeleton first unearthed in 1994. The fossil is the remains of a small-brained 50-kilogram (110 lb) female, nicknamed "Ardi", and includes most of the skull and teeth, as well as the pelvis, hands, and feet.[8] It was discovered in Ethiopia's harsh Afar desert at a site called Aramis in the Middle Awash region. Radiometric dating of the layers of volcanic ash encasing the deposits revealed that Ardi lived 4.4 million years ago.

The fossil sheds light on a stage of human evolution about which little was known, more than a million years before Lucy (Australopithecus afarensis), the iconic early human ancestor candidate who lived 3.2 million years ago, and was discovered in 1974 just 74 km (46 mi) away from Ardi's discovery site.

Researchers infer from the form of her pelvis and limbs and the presence of her abductable hallux, that she was a facultative biped: bipedal when moving on the ground, but quadrupedal when moving about in tree branches.[2][9][10] A. ramidus had a more primitive walking ability than later hominids, and could not walk or run for long distances.[11] The teeth suggest omnivory, and are more generalised than those of modern apes.[2]

Ardipithecus kadabba

Ardipithecus kadabba fossils

Ardipithecus kadabba is "known only from teeth and bits and pieces of skeletal bones",[8] and is dated to approximately 5.6 million years ago.[2] It has been described as a "probable chronospecies" (i.e. ancestor of A. ramidus).[2] Although originally considered a subspecies of A. ramidus, in 2004 anthropologists Yohannes Haile-Selassie, Gen Suwa, and Tim D. White published an article elevating A. kadabba to species level on the basis of newly-discovered teeth from Ethiopia. These teeth show "primitive morphology and wear pattern" which demonstrate that A. kadabba is a distinct species from A. ramidus.[12]

The specific name comes from the Afar word for "basal family ancestor".[13]

Lifestyle

The toe and pelvic structure of A. ramidus suggests that the creature walked upright.[4]

According to Scott Simpson, the Gona Project's physical anthropologist, the fossil evidence from the Middle Awash indicates that both A. kadabba and A. ramidus lived in "a mosaic of woodland and grasslands with lakes, swamps and springs nearby," but further research is needed to determine which habitat Ardipithecus at Gona preferred.[4]

See also

References

  1. ^ Perlman, David (July 12, 2001). "Fossils From Ethiopia May Be Earliest Human Ancestor". National Geographic News. http://news.nationalgeographic.com/news/2001/07/0712_ethiopianbones.html. Retrieved July 2009. "Another co-author is Tim D. White, a paleoanthropologist at UC-Berkeley who in 1994 discovered a pre-human fossil, named Ardipithecus ramidus, that was then the oldest known, at 4.4 million years."  
  2. ^ a b c d e f White, Tim D.; Asfaw, Berhane; Beyene, Yonas; Haile-Selassie, Yohannes; Lovejoy, C. Owen; Suwa, Gen; WoldeGabriel, Giday (2009). "Ardipithecus ramidus and the Paleobiology of Early Hominids.". Science 326 (5949): 75–86. doi:10.1126/science.1175802.  
  3. ^ Tyson, Peter (October 2009). "NOVA, Aliens from Earth: Who's who in human evolution". PBS. http://www.pbs.org/wgbh/nova/hobbit/tree-nf.html. Retrieved 2009-10-08.  
  4. ^ a b c "New Fossil Hominids of Ardipithecus ramidus from Gona, Afar, Ethiopia". http://www.stoneageinstitute.org/news/gona_nature_paper.shtml#1. Retrieved 2009-01-30.  
  5. ^ Indiana University News Release. "Anthropologists find 4.5 million-year-old hominid fossils in Ethiopia". http://newsinfo.iu.edu/news/page/normal/1822.html. Retrieved 2009-01-30.  
  6. ^ Suwa, G et al (2 October 2009). "The Ardipithecus ramidus skull and its implications for hominid origins". Science 326 (5949): 68, 68e1-68e7. doi:10.1126/science.1175825.  
  7. ^ a b Suwa, G et al (2 October 2009). "Paleobiological implications of the Ardipithecus ramidus dentition". Science 326 (5949): 69, 94-99. doi:10.1126/science.1175824.  
  8. ^ a b Gibbons, Ann (2009). "A New Kind of Ancestor: Ardipithecus Unveiled". Science 326 (5949): 36–40. doi:10.1126/science.326_36.  
  9. ^ Jamie Shreeve (2009-10-01). "Oldest Skeleton of Human Ancestor Found". National Geographic magazine. http://news.nationalgeographic.com/news/2009/10/091001-oldest-human-skeleton-ardi-missing-link-chimps-ardipithecus-ramidus.html. Retrieved 2009-10-01.  
  10. ^ Ann Gibbons. "Ancient Skeleton May Rewrite Earliest Chapter of Human Evolution". Science magazine. http://sciencenow.sciencemag.org/cgi/content/full/2009/1001/1. Retrieved 2009-10-01.  
  11. ^ BBC: Fossil finds extend human story
  12. ^ Haile-Selassie, Yohannes; Suwa, Gen; White, Tim D. (2004). "Late Miocene Teeth from Middle Awash, Ethiopia, and Early Hominid Dental Evolution". Science 303 (5663): 1503–1505. doi:10.1126/science.1092978. PMID 15001775.  
  13. ^ Ellis, Richard (2004). No Turning Back: The Life and Death of Animal Species. New York: Harper Perennial. pp. 92. ISBN 0-06-055804-0.  

External links


Wikispecies

Up to date as of January 23, 2010

From Wikispecies

Taxonavigation

Main Page
Cladus: Eukaryota
Supergroup: Unikonta
Cladus: Opisthokonta
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Cladus: Deuterostomia
Phylum: Chordata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Superclassis: Tetrapoda
Classis: Mammalia
Subclassis: Theria
Infraclassis: Placentalia
Ordo: Primates
Subordo: Haplorrhini
Infraordo: Simiiformes
Parvordo: Catarrhini
Superfamilia: Hominoidea
Familia: Hominidae
Subfamilia: Homininae
Tribus: Hominini
Subtribus: Hominina
Genus: †Ardipithecus
Species: A. kadabba - A. ramidus

Name

Ardipithecus, White et al., 1995

Vernacular names

Español: Ardipitecos
עברית: ארדיפיתקוס
日本語: アルディピテクス属
Wikimedia Commons For more multimedia, look at Ardipithecus on Wikimedia Commons.

Simple English

Ardipithecus
Fossil range: Pliocene
File:Ardipithecus kadabba
Ardipithecus kadabba fossils
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Family: Hominidae
Subfamily: Homininae
Tribe: Hominini
Genus: Ardipithecus
White et al., 1995
Species

Ardipithecus kadabba
Ardipithecus ramidus

Ardipithecus is a very early human of the genus, 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.


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