Sahelanthropus tchadensis

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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 fossil hominid that lived approximately 7 million years ago. Its position in the Hominid evolution is not widely accepted.

1 Fossils
2 Relationship to modern humans and great apes
3 See also
4 Footnotes
5 References
6 External links

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 Tebou 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, although some paleontologists have disputed this interpretation of the basicranium. Its canine wear is similar to other Miocene apes.^[2]

The fossils were discovered in the Djurab desert of Chad by a team of four; three Chadians, Adoum Mahamat, Djimdoumalbaye Ahounta and Gongdibé Fanone, and the French team leader Alain Beauvilain.^[3]^[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 the Sahelanthropus' discoverers as early as 1993.^[2]

Relationship to modern humans and great apes

Sahelanthropus may represent a common ancestor of humans and chimpanzees;no concessus 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.^[6]

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,^{[citation needed]} 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 partially exposed in loose sand; co-discoverer Beauvilain cautions that such sediment can be easily moved by the wind, unlike packed earth. 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. 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.^[7]

Footnotes

^ 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.
^ ^a ^b Brunet et al. (2002, 2005)
^ Toumaï : Histoire des Sciences et Histoire d’Hommes - Alain Beauvilain - Tchad Actuel]
^ Web site of Alain Beauvilain
^ Press Material on Toumaï discovery - Centre National de la Recherche Scientifique (french)
^ Guy et al. (2005), Wolpoff et al. (2006)
^ Brunet et al. (2005), Beauvilain (2008)

References

Beauvilain, Alain (2008). "The contexts of discovery of Australopithecus bahrelghazali (Abel) and of Sahelanthropus tchadensis (Toumaï): unearthed, embedded in sandstone, or surface collected?". South African Journal of Science 104 (5/6): pp. 165-168. ^{[verification needed]}
Brunet et al. (2002): "A new hominid from the Upper Miocene of Chad, Central Africa." Nature 418(6894): 145–151. doi:10.1038/nature00879 PDF fulltext. Erratum: Nature 418(6899): 801. doi:10.1038/nature01005 PDF fulltext
Brunet et al. (2005): "New material of the earliest hominid from the Upper Miocene of Chad." Nature 434(6894): 752-755. doi:10.1038/nature03392 PDF fulltext
Guy et al. (2005): "Morphological affinities of the Sahelanthropus tchadensis (Late Miocene hominid from Chad) cranium." PNAS 102(52): 18836–18841. doi:10.1073/pnas.0509564102 PDF fulltext Supporting Tables
Wolpoff et al. (2006): "An Ape or the Ape: Is the Toumaï Cranium TM 266 a Hominid?" PaleoAnthropology 2006: 36–50. PDF fulltext

External links

Wikispecies has information related to: Sahelanthropus

v • d • e Part of the series on Human evolution


Hominini
Sahelanthropus tchadensis • Orrorin tugenensis • Ardipithecus • Kenyanthropus platyops
Australopithecines
Australopithecus: A. anamensis • A. afarensis • A. bahrelghazali • A. africanus • A. garhi Paranthropus: P. aethiopicus • P. boisei • P. robustus
Humans and Proto-humans
Homo: H. habilis • H. rudolfensis • H. georgicus • H. ergaster • H. erectus (H. e. lantianensis • H. e. palaeojavanicus • H. e. pekinensis • H. e. nankinensis • H. e. wushanensis • H. e. yuanmouensis • H. e. soloensis) • H. cepranensis • H. antecessor • H. heidelbergensis • H. neanderthalensis • H. rhodesiensis • H. floresiensis • Archaic Homo sapiens • Anatomically modern humans (H. s. idaltu • H. s. sapiens)
Topics: Timeline of human evolution • List of human evolution fossils • Human evolutionary genetics
Models: Recent African origin• Multiregional evolution