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Sahelanthropus tchadensis
"Toumaï"
Fossil range: Late Miocene
Sahelanthropus tchadensis skull (Toumai)
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Family: Hominidae
Subfamily: Homininae
Tribe: Hominini
Subtribe: Hominina
Genus: Sahelanthropus
Brunet et al., 2002[1]
Species: S. tchadensis
Binomial name
Sahelanthropus tchadensis
Brunet et al., 2002

Sahelanthropus tchadensis is a name of a fossil that is dated to about 7 million years ago. Its exact position—if the fossil can be regarded as part of the hominidae tree—is not made clear but there are arguments supporting and denying its place in the hominid tree. Another complication in its classification and understanding is because it is one of the earliest dated hominid fossils and very few or if not any bone evidence other than the partial cranium. It is dated about 3 million years earlier than the Australopithecines, earliest of which are dated to about 4 million years ago.

Contents

Fossils

Location of discovery
Detail of map
Restoration of the face of Sahelanthropus

Existing fossils – a relatively small cranium nicknamed Toumaï ("hope of life" in the local Dazaga language of Chad), five pieces of jaw and some teeth – make up a head that has a mixture of derived and primitive features. The braincase, being only 340 cm³ to 360 cm³ in volume is similar to that of extant chimpanzees and is notably less than the approximate human volume of 1350 cm³. The teeth, brow ridges, and facial structure differ markedly from those found in Homo sapiens. Due to the distortion that the cranium has suffered, a 3D computer reconstruction has not been produced.

Since no postcranial remains (bones below the skull) have been discovered, it is as of yet unknown whether Sahelanthropus tchadensis was indeed bipedal, although claims for an anteriorly placed foramen magnum suggests that this may have been the case, some paleontologists have disputed this interpretation of the basicranium. Its canine wear is similar to other Miocene apes.[2] Moreover, according to recent information, the femur of an hominid may have been discovered alongside the cranium but never published.[3]

The fossils were discovered in the Djurab desert of Chad by a team of four lead by Michel Brunet; three Chadians, Adoum Mahamat, Djimdoumalbaye Ahounta and Gongdibé Fanoné, and Frenchman, Alain Beauvilain.[4] · [5] All known material of Sahelanthropus were found between July 2001 to March 2002 at three sites (TM 247, TM 266 which yielded most of the material, and TM 292). The discoverers claimed that S. tchadensis is the oldest known human ancestor after the split of the human line from that of chimpanzees. The bones were found far from most previous hominin fossil finds, which are from Eastern and Southern Africa. However, an Australopithecus bahrelghazali mandible was found in Chad by Beauvilain A., Brunet M. and Moutaye A.H.E. as early as 1995.[6]

Relationship to modern humans and great apes

Sahelanthropus may represent a common ancestor of humans and chimpanzees; no consensus has been reached yet by the scientific community. The original placement of this species as a human ancestor but not a chimpanzee ancestor would complicate the picture of human phylogeny. In particular, if Toumaï is a direct human ancestor, then its facial features bring the status of Australopithecus into doubt because its thickened brow ridges were reported to be similar to those of some later fossil hominids (notably Homo erectus), whereas this morphology differs from that observed in all australopithecines, most fossil hominids and extant humans.

Another possibility is that Toumaï is related to both humans and chimpanzees, but is the ancestor of neither. Brigitte Senut and Martin Pickford, the discoverers of Orrorin tugenensis, suggested that the features of S. tchadensis are consistent with a female proto-gorilla. Even if this claim is upheld, then the find would lose none of its significance, for at present precious few chimpanzee or gorilla ancestors have been found anywhere in Africa. Thus if S. tchadensis is an ancestral relative of the chimpanzees (or gorillas) then it represents the first known member of their lineage. Furthermore, S. tchadensis does indicate that the last common ancestor of humans and chimpanzees is unlikely to resemble chimpanzees very much, as had been previously supposed by some paleontologists.[7] · [8] Unfortunately, the exact age of the fossil is somewhat hard to determine. While molecular clocks are increasingly found to be far more unreliable than initially believed[9] sediment isotope analysis which yielded an age of about 7 million years is generally considered quite reliable. In this case however, the fossils were found exposed in loose sand; co-discoverer Beauvilain cautions that such sediment can be easily moved by the wind, unlike packed earth.[10] In fact, Toumaï was probably reburied in the recent past. Taphonomic analysis reveals the likelihood of one, perhaps two, burial(s) which seemingly occurred after the introduction of Islam in the region. Two other hominid fossils (a left femur and a mandible) were in the same “grave” along with various mammal remains.The sediment surrounding the fossils might thus not be the material the bones were originally deposited in, making it necessary to corroborate the fossil's age by some other means.[11] The fauna found at the site – namely the anthracotheriid Libycosaurus petrochii and the suid Nyanzachoerus syrticus – suggests an age of more than 6 million years, as these species were probably extinct already by that time.[12]

See also

Notes

  1. ^ Usually, all authors of a taxon description are cited. In this case they are so many however that for layout reasons the list is abbreviated. The full citation is:
    Brunet, Guy, Pilbeam, Mackaye, Likius, Ahounta, Beauvilain, Blondel, Bocherens, Boisserie, De Bonis, Coppens, Dejax, Denys, Duringer, Eisenmann, Fanone, Fronty, Geraads, Lehmann, Lihoreau, Louchart, Mahamat, Merceron, Mouchelin, Otero, Pelaez Campomanes, Ponce de León, Rage, Sapanet, Schuster, Sudre, Tassy, Valentin, Vignaud, Viriot, Zazzo, & Zollikofer, 2002.
  2. ^ Brunet, Guy, Pilbeam, Mackaye, Likius, Djimdoumalbaye, Beauvilain, Blondel, Bocherens, Boisserie, De Bonis, Coppens, Dejax, Denys, Duringer, Eisenmann, Gongdibé, Fronty, Geraads, Lehmann, Lihoreau, Louchart, Adoum, Merceron, Mouchelin, Otero, Pelaez Campomanes, Ponce De Leon, Rage, Sapanet, Schuster, Sudre, Tassy, Valentin, Vignaud, Viriot, Zazzo & Zollikofer, 2002. A new hominid from the Upper Miocene of Chad, Central Africa, Nature, 418 (6894): 145-151.
  3. ^ Hawks 2009 Sahelanthropus: The femur of Toumaï?
  4. ^ Tchad Actuel Toumaï : Histoire des Sciences et Histoire d’Hommes
  5. ^ Web site of Alain Beauvilain
  6. ^ Brunet M., Beauvilain A., Coppens Y., Heintz E., Moutaye A.H.E. et Pilbeam D., 1995. The first australopithecine 2,500 kilometres west of the Rift Valley (Chad) Nature, 378 (6554): 273-275. résumé]
  7. ^ Guy F., Lieberman D. E., Pilbeam D., Ponce de Leon M. S., Likius A., Mackaye H. T., Vignaud P., Zollikofer C. P. E. et Brunet M., 2006. Morphological affinities of the Sahelanthropus tchadensis (Late Miocene hominid from Chad) cranium [1] PDF fulltext Supporting Tables, PNAS, 102 (52) : 18836-18841.
  8. ^ Wolpoff M. H., Hawks J., Senut B., Pickford M. et Ahern J., 2006. An Ape or the Ape : Is the Toumaï Cranium TM 266 a Hominid?, PaleoAnthropology, 2006: 36-50.
  9. ^ Lebatard A.-E., Bourles D. L., Duringer P., Jolivet M., Braucher R., Carcaillet J., Schuster M., Arnaud N., Monie P., Lihoreau F., Likius A., Mackaye H. T., Vignaud P. et Brunet M., 2008. Cosmogenic nuclide dating of Sahelanthropus tchadensis and Australopithecus bahrelghazali: Mio-Pliocene hominids from Chad. PNAS 105(9): 3226-3231 PDF fulltext
  10. ^ Beauvilain 2008 The contexts of discovery of Australopithecus bahrelghazali and of Sahelanthropus tchadensis (Toumaï) : unearthed, embedded in sandstone or surface collected ? South african Journal of Science, 104 (3): 165-168.
  11. ^ Beauvilain and Watté, 2009. Toumaï ("Sahelanthropus tchadensis") a-t-il été inhumé ? Bulletin de la Société géologique de Normandie et des Amis du Museum du Havre, 96 (1): 19-26.
  12. ^ Brunet M., Guy F., Pilbeam D., Lieberman D. E., Likius A., Mackaye H. T., Ponce de Leon M. S., Zollikofer C. P. E. et Vignaud P., 2005. New material of the earliest hominid from the Upper Miocene of Chad. Nature, 434 (7034): 752-755

References

  • Beauvilain Alain, 2003. Toumaï, l’aventure humaine. La Table Ronde, Paris, 239 p. ISBN 978-2-7103-2592-5.
  • Brunet Michel, 2006. D’Abel à Toumaï. Nomade, chercheur d’os. Odile Jacob, Paris, 254 p. ISBN 978-2-7381-1738-0.
  • Gibbons Ann, 2006. The first human.. Doubleday, New York, 306 p. ISBN 978-0-385-51226-0.

External links

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Wikispecies

Up to date as of January 23, 2010

From Wikispecies

Sahelanthropus tchadensis skull (Toumai)

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: †Sahelanthropus
Species: Sahelanthropus tchadensis

Name

Sahelanthropus tchadensis Brunet et al., 2002

References

  • Brunet, M. et al. 2002: A new hominid from the upper Miocene of Chad, central Africa. Nature (London), 418: 145-151.
Wikimedia Commons For more multimedia, look at Sahelanthropus tchadensis on Wikimedia Commons.

Simple English

Sahelanthropus tchadensis
Fossil range: Late Miocene
File:Sahelanthropus tchadensis - TM
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Family: Hominidae
Subfamily: Homininae
Tribe: Hominini
Subtribe: Hominina
Genus: Sahelanthropus
Brunet et al, 2002
Species: S. tchadensis
Binomial name
Sahelanthropus tchadensis
Brunet et al, 2002

Sahelanthropus tchadensis is a fossil hominid. From evidence at the fossil site in Chad in the African Sahel, it is thought to have lived about 7 million years ago.

The split of the line into humans and chimpanzees (known as human-chimpanzee divergence) probably happened between 6.3 and 5.4 million years ago. This can be seen from genetic data.[1] Because the fossil is older than this spilt, its status is unclear. The first fossil found is known as Toumaï today.

Contents

Fossils

Some fossils, a cranium (skull), five pieces of jaw, and some teeth, make up a head that has features that are like both modern and primitive humans. The braincase is only 340 cm³ to 360 cm³ in volume, about the same as chimpanzees. It is much less than the human volume of about 1350 cm³.

The teeth and structure of the face are very different from Homo sapiens. The cranium found is damaged, it is very distorted, so no 3D computer reconstruction has been made. There are no bones other than parts of the skull. It is unknown if Sahelanthropus tchadensis was bipedal (walked on two legs). The placement of the foramen magnum suggests they were, though. Its canine wear is similar to other Miocene apes.

Relationship to modern humans and great apes

Sahelanthropus may be an ancestor of both humans and chimpanzees; no consensus has been reached yet by the scientific community. The difficulty is caused by its "mosaic of primitive and derived features".[2] Probably it lived in semi-open woodland and savannah, rather than the rainforest of present-day apes.[3]

Another possibility is that Toumaï is related to both humans and chimpanzees, but is the ancestor of neither. Brigitte Senut and Martin Pickford, the discoverers of Orrorin tugenensis, suggested that the features of S. tchadensis are consistent with a female proto-gorilla. Even if this claim is upheld, the find would still be significant, for at present few chimpanzee or gorilla ancestors have been found anywhere in Africa. Thus, if S. tchadensis is an ancestral relative of the chimpanzees (or gorillas), it represents the first known member of their lineage.

Furthermore, S. tchadensis does indicate that the last common ancestor of humans and chimpanzees is unlikely to resemble chimpanzees very much, as had been previously supposed by some paleontologists.[2][3]

The fauna found at the site suggest an age of more than 6 million years, as these species were probably extinct already by that time.[4]

Related pages

References

  1. "Evolution's human and chimp twist". BBC. May 18, 2006. http://news.bbc.co.uk/2/hi/science/nature/4991470.stm. Retrieved April 2010. 
  2. 2.0 2.1 Guy F. et al 2005. Morphological affinities of the Sahelanthropus tchadensis (Late Miocene hominid from Chad) cranium. [1] PDF fulltext Supporting Tables PNAS, 102: 18836-18841.
  3. 3.0 3.1 Wolpoff M.H., et al 2006. an Ape or the Ape : is the Toumaï cranium TM 266 a Hominid?, PaleoAnthropology, 2006: 36-50.
  4. Brunet M. et al 2005. New material of the earliest hominid from the Upper Miocene of Chad. Nature, 434: 752-755
  • Brunet, Michel; et al. (2002). [Expression error: Unexpected < operator "A new hominid from the Upper Miocene of Chad, Central Africa"]. Nature 418: 145–151. doi:10.1038/nature00879. 
  • Brunet, Michel; et al. (2005). [Expression error: Unexpected < operator "New material of the earliest hominid from the Upper Miocene of Chad"]. Nature 434: 752–755. doi:10.1038/nature03392. 
  • Guy, Franck; et al. (2005). [Expression error: Unexpected < operator "Morphological affinities of the Sahelanthropus tchadensis (Late Miocene hominid from Chad) cranium"]. Proceedings of the National Academy of Science 102 (52): 18836–18841. 
  • Wolpoff, M. H.; et al. (2006). "An Ape or the Ape: Is the Toumaï Cranium TM 266 a Hominid?". PaleoAnthropology 2006: 36–50. http://www.paleoanthro.org/journal/content/PA20060036.pdf. 

Other websites

Look up Sahelanthropus in Wikispecies, a directory of species


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