Overview

Brief Summary

Where Lived: Western Africa (Chad)

When Lived: Sometime between 7 and 6 million years ago

Sahelanthropus tchadensis is one of the oldest known species on the human family tree. This species lived sometime between 7 and 6 million years ago in West-Central Africa (Chad). Walking upright may have helped this species survive in the diverse habitats—including forests and grasslands Though we only have cranial material from Sahelanthropus, studies so far indicates this early human had a combination of apelike and humanlike features. Their apelike features included a small brain (even slightly smaller than a chimpanzee’s!) sloping face, very prominent brow ridges, and elongated skull. Their humanlike features included small canine teeth, a short middle part of the face, and a spinal cord opening beneath the skull instead of towards the back, like in nonbipedal primates (or apes).

How do we know Sahelanthropus walked upright?

Some of the oldest evidence for walking on two legs comes from Sahelanthropus. The large opening (foramen magnum) in the base of the cranium where the spinal cord connects with the brain is positioned further forward (the underside of the cranium) than in apes or any other primate except humans. This feature indicates that the head of Sahelanthropus was held on an upright body.

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Physical Description

Size

Because scientists have only recovered a single skull and some jaw and tooth fragments belonging to Sahelanthropus (no post-cranial fossils), we don’t know yet exactly how big an individual of this species would have been. Given the size of TM 266-01-060-1 skull, scientists estimate that Sahelanthropus individuals would probably be similar in size to a chimpanzee.

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Type Information

Key Fossils

TM 266-01-060-1

Nickname: Toumai

Site: Toros-Menalla, Chad

Date of discovery: 2001

Discovered by: A team led by Michel Brunet

Age: Between 7 and 6 million years old

Species: Sahelanthropus tchadensis

One of the first human traits, the small canine teeth in this male skull distinguished it from other apes. Most male primates have long canine teeth that they use to threaten and harm other males. There may have been less competition among Sahelanthropus tchadensis males, or perhaps males expressed aggression in other ways. This skull, nearly complete though flattened by distortion, is also known by its nickname, ‘Toumai,’ which means ‘hope of life’ in the local Dazaga language of Chad.

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Life History and Behavior

Behavior

How They Survived

Unfortunately, most of Sahelanthropus’ teeth are heavily worn, and there have not yet been studies of its tooth wear or tooth isotopes to indicate diet. However, we can infer based on its environment and other early human species that it ate a mainly plant-based diet. This probably included leaves, fruit, seeds, roots, nuts, and insects.

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Evolution and Systematics

Evolution

Evolutionary Tree Information

The first early humans, or hominins, diverged from apes sometime between 6 and 7 million years ago in Africa. Sahelanthropus tchadensis has two defining human anatomical traits; 1) small canine teeth, and 2) walking upright on two legs instead of on four legs.

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Fossil History

History of Discovery

Year of Discovery: 2001



The first (and, so far, only) fossils of Sahelanthropus are nine cranial specimens from northern Chad. A research team of scientists led by French paleontologist Michael Brunet uncovered the fossils in 2001, including the type specimen TM 266-01-0606-1. Before 2001, early humans in Africa had only been found in the great rift valley in East Africa and sites in South Africa, so the discovery of Sahelanthropus fossils in West-Central Africa shows that the earliest humans were more widely distributed than previously thought.

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Wikipedia

Sahelanthropus

Sahelanthropus tchadensis is an extinct hominine species that is dated to about 7 million years ago, possibly very close to the time of the chimpanzee/human divergence, and so it is unclear whether it can be regarded as a member of the Hominini tribe.[1] Few specimens are known, other than the partial skull nicknamed Toumaï ("hope of life").

Fossils[edit]

Location of discovery.
Detail of map.

Existing fossils include a relatively small cranium known as Toumaï ("hope of life" in the local Dazaga language of Chad in central Africa), five pieces of jaw, and some teeth, making up a head that has a mixture of derived and primitive features. The braincase, being only 320 cm³ to 380 cm³ in volume, is similar to that of extant chimpanzees and is notably less than the approximate human volume of 1350 cm³.[citation needed]

The teeth, brow ridges, and facial structure differ markedly from those found in Homo sapiens. Cranial features show a flatter face, u-shaped dental arcade, small canines, an anterior foramen magnum, and heavy brow ridges. No postcranial remains have been recovered. The fossil suffered a large amount of distortion during the time of fossilisation and discovery.[citation needed]

Because no postcranial remains (i.e., bones below the skull) have been discovered, it is not known definitively whether Sahelanthropus tchadensis was indeed bipedal or two-footed, although claims for an anteriorly placed foramen magnum suggests that this may have been the case. Some paleontologists[who?] have disputed[why?] this interpretation of the basicranium. Its canine wear is similar to other Miocene apes.[2] Moreover, according to recent information, the femur of a hominid might have been discovered alongside the cranium but never published.[3]

Discovery[edit]

The fossils were discovered in the Djurab Desert of Chad by a team of four led by Michel Brunet; three Chadians, Adoum Mahamat, Djimdoumalbaye Ahounta and Gongdibé Fanoné, and Frenchman, Alain Beauvilain et al.[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.[6]

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] With the sexual dimorphism known to have existed in early hominids, the difference between Ardipithecus and Sahelanthropus may not be large enough to warrant a separate species for the latter.[7]

Relationship to humans and chimpanzees[edit]

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 into doubt the status of Australopithecus 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.[8][9]

A further possibility, highlighted by research published in 2012, is that the human/chimpanzee split is earlier than previously thought, with a possible range of 7 to 13 million years ago (with the more recent end of this range being favoured by most researchers), based on slower than previously thought changes between generations in human DNA. Indeed, some researchers (such as Tim D. White, University of California) consider suggestions that Sahelanthropus is too early to be a human ancestor to have evaporated.[10]

Sediment isotope analysis of cosmogenic atoms in the fossil yielded an age of about 7 million years.[11] 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.[12]

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 in which the bones were originally deposited, making it necessary to corroborate the fossil's age by some other means.[13] 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 already extinct by that time.[14]

See also[edit]

Notes[edit]

  1. ^ a b c Klages, Arthur (2008) "Sahelanthropus tchadensis: An Examination of its Hominin Affinities and Possible Phylogenetic Placement," Totem: The University of Western Ontario Journal of Anthropology: Vol. 16: Iss. 1, Article 5. http://ir.lib.uwo.ca/totem/vol16/iss1/5
  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. ^ a b 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. ^ 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. 
  8. ^ 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., (27 December 2005). "Morphological affinities of the Sahelanthropus tchadensis (Late Miocene hominid from Chad) cranium" [1] PDF fulltext Supporting Tables, PNAS, 102 (52) : 18836–18841.
  9. ^ 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.
  10. ^ Catherine Brahic (24 Nov 2012). "Our True Dawn". New Scientist (Reed Business Information) (2892): 34–7. ISSN 0262-4079. , citing research by Augustine Kong (Decode Genetics, Reykjavik), David Reich (Harvard) and others
  11. ^ 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
  12. ^ 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.
  13. ^ 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.
  14. ^ 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[edit]

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Notes

The Unknown

We don’t know everything about our early ancestors—but we keep learning more! Paleoanthropologists are constantly in the field, excavating new areas with groundbreaking technology, and continually filling in some of the gaps about our understanding of human evolution. Below are some of the still unanswered questions about Sahelanthropus tchadensis that may be answered with future discoveries:

1. What did the body of Sahelanthropus tchadensis look like? So far paleoanthropologists have only uncovered cranial fossils of this species.

2. What was their primary form of locomotion?

3. What did they eat?

4. Why did Sahelanthropus tchadensis males have smaller canines? This is unlike male chimpanzees and most other primates who use their long canine teeth to threaten others, especially when competing for mates.

5. Were there size differences between Sahelanthropus tchadensis males and females?

6. Was Sahelanthropus tchadensis a common ancestor of humans and chimpanzees?

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