From Wikipedia, the free encyclopedia
Jump to: navigation, search
Temporal range: Late Miocene - Early Pliocene, 5.6–4.4Ma
Ardipithecus ramidus specimen, nicknamed Ardi
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Family: Hominidae
Subfamily: Homininae
Tribe: (debated[1] Hominini)
Genus: Ardipithecus
White et al., 1995

Ardipithecus kadabba
Ardipithecus ramidus

Ardipithecus is a fossil hominine. It is still a matter of debate what was the relation of this genus to human ancestors, and whether it is a hominin, or not.[1] Two species are described in the literature: A. ramidus, which lived about 4.4 million years ago[2] during the early Pliocene, and A. kadabba, dated to approximately 5.6 million years ago (late Miocene).[3]

Ardipithecus ramidus[edit]

Map showing discovery locations.

A. ramidus was named in September 1994. The first fossil found was dated to 4.4 million years ago on the basis of its stratigraphic position between two volcanic strata: the basal Gaala Tuff Complex (GATC) and the Daam Aatu Basaltic Tuff (DABT).[4] The name Ardipithecus ramidus stems mostly from the Afar language, in which Ardi means "ground/floor" (borrowed from the Semitic root in either Amharic or Arabic) and ramid means "root". The pithecus portion of the name is from the Greek word for "ape".[5]

Like most hominids, but unlike all previously recognized hominins, it had a grasping hallux or big toe adapted for locomotion in the trees. It is not confirmed how much other features of its skeleton reflect adaptation to bipedalism on the ground as well. Like later hominins, Ardipithecus had reduced canine teeth.

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.[6] The fossils were dated to between 4.35 and 4.45 million years old.[7]

Ardipithecus ramidus had a small brain, measuring between 300 and 350 cm3. This is slightly smaller than 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.[8]

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 foliage, fibrous plant material (roots, tubers, etc.), or hard and or abrasive food. The size of the upper canine tooth in A. ramidus males was not distinctly different from 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 the 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.[9]

The less pronounced nature of the 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."[9]

A. ramidus existed more recently than the most recent common ancestor of humans and chimpanzees (CLCA or Pan-Homo LCA) 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.[3]


Main article: 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.[10] 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 suggest that Ardi lived about 4.4 million years ago. This date, however, has been questioned by others. Fleagle and Kappelman suggest that the region in which Ardi was found is difficult to date radiometrically, and they argue that Ardi should be dated at 3.9 million years.[11]

The fossil is regarded by its describers as shedding 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. However, because the "Ardi" skeleton is no more than 200,000 years older than the earliest fossils of Australopithecus, and may in fact be younger than they are,[11] some researchers doubt that it can represent a direct ancestor of Australopithecus.

Some researchers infer from the form of her pelvis and limbs and the presence of her abductable hallux, that "Ardi" was a facultative biped: bipedal when moving on the ground, but quadrupedal when moving about in tree branches.[3][12][13] A. ramidus had a more primitive walking ability than later hominids, and could not walk or run for long distances.[14] The teeth suggest omnivory, and are more generalised than those of modern apes.[3]

Ardipithecus kadabba[edit]

Ardipithecus kadabba fossils.

Ardipithecus kadabba is "known only from teeth and bits and pieces of skeletal bones",[10] and is dated to approximately 5.6 million years ago.[3] It has been described as a "probable chronospecies" (i.e. ancestor) of A. ramidus.[3] 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.[15]

The specific name comes from the Afar word for "basal family ancestor".[16]


The toe and pelvic structure of A. ramidus suggest to some researchers that the organism walked upright.[6]


Alternative views[edit]

Researchers outside the original (2009) group of describers have not yet studied the fossils of Ardipithecus, and the paleobiology and relationships of these creatures have become the subject of controversy.[17][18] Skeptics[which?] claim that many[quantify] of the allegedly hominin-like features seen in the Ardipithecus material appear elsewhere among living and fossil primates, and that the available evidence does not adequately support claims about its hominin status and locomotor habits.[1]

See also[edit]


  1. ^ a b c Stanford, Craig B. (2012). "Chimpanzees and the Behavior ofArdipithecus ramidus*". Annual Review of Anthropology 41: 139. doi:10.1146/annurev-anthro-092611-145724. "Is Ardipithecus a hominin?—that question will likely dominate the paleoanthropological debate over this fossil taxon for years to come." 
  2. ^ Perlman, David (July 12, 2001). "Fossils From Ethiopia May Be Earliest Human Ancestor". National Geographic News. 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." 
  3. ^ 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. Bibcode:2009Sci...326...64W. doi:10.1126/science.1175802. PMID 19810190. 
  4. ^ White, T. D.; Suwa, G.; Asfaw, B. (1994). "Australopithecus ramidus, a new species of early hominid from Aramis, Ethiopia". Nature 371 (6495): 306–312. Bibcode:1994Natur.371..306W. doi:10.1038/371306a0. PMID 8090200.  edit
  5. ^ Tyson, Peter (October 2009). "NOVA, Aliens from Earth: Who's who in human evolution". PBS. Retrieved 2009-10-08. 
  6. ^ a b c "New Fossil Hominids of Ardipithecus ramidus from Gona, Afar, Ethiopia". Archived from the original on 2008-06-24. Retrieved 2009-01-30. 
  7. ^ Indiana University News Release. "Anthropologists find 4.5 million-year-old hominid fossils in Ethiopia". Archived from the original on 14 February 2009. Retrieved 2009-01-30. 
  8. ^ Suwa, G et al.; Asfaw, B.; Kono, R. T.; Kubo, D.; Lovejoy, C. O.; White, T. D. (2 October 2009). "The Ardipithecus ramidus skull and its implications for hominid origins". Science 326 (5949): 68, 68e1–68e7. Bibcode:2009Sci...326...68S. doi:10.1126/science.1175825. PMID 19810194. 
  9. ^ a b Suwa, G et al.; Kono, R. T.; Simpson, S. W.; Asfaw, B.; Lovejoy, C. O.; White, T. D. (2 October 2009). "Paleobiological implications of the Ardipithecus ramidus dentition". Science 326 (5949): 69, 94–99. Bibcode:2009Sci...326...94S. doi:10.1126/science.1175824. PMID 19810195. 
  10. ^ a b Gibbons, Ann (2009). "A New Kind of Ancestor: Ardipithecus Unveiled". Science 326 (5949): 36–40. Bibcode:2009Sci...326...36G. doi:10.1126/science.326_36. PMID 19797636. 
  11. ^ a b Kappelman, John; Fleagle, John G. (1995). "Age of early hominids". Nature 376 (6541): 558–559. Bibcode:1995Natur.376..558K. doi:10.1038/376558b0. 
  12. ^ Jamie Shreeve (2009-10-01). "Oldest Skeleton of Human Ancestor Found". National Geographic magazine. Archived from the original on 4 October 2009. Retrieved 2009-10-01. 
  13. ^ Ann Gibbons. "Ancient Skeleton May Rewrite Earliest Chapter of Human Evolution". Science magazine. Archived from the original on 4 October 2009. Retrieved 2009-10-01. 
  14. ^ Amos, Jonathan (2009-10-01). "Fossil finds extend human story". BBC News. 
  15. ^ 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. Bibcode:2004Sci...303.1503H. doi:10.1126/science.1092978. PMID 15001775. 
  16. ^ Ellis, Richard (2004). No Turning Back: The Life and Death of Animal Species. New York: Harper Perennial. p. 92. ISBN 0-06-055804-0. 
  17. ^ Sarmiento, Esteban E. (2010). "Comment on the Paleobiology and Classification of Ardipithecus ramidus". Science 328: 1105b. doi:10.1126/science.1184148. 
  18. ^ Wood, Bernard; Harrison, Terry (2011). "The evolutionary context of the first hominins". Nature 470 (7334): 347–352. Bibcode:2011Natur.470..347W. doi:10.1038/nature09709. 

External links[edit]