Sahelanthropus tchadensis,
Toumaï Shows the Teeth II
Sahelanthropus tchadensis: the facts
Michel Brunet and MPFT†
Sir, In a recent article in this journal, Beauvilain and Le Guellec suggest that our initial description of Sahelanthropus tchadensis (2) was flawed by the inaccurate identification and association of specimens. Their claims are without foundation. Beauvilain and Le Guellec (1) offered supplementary information on the hypodigm and geological context of the oldest known hominid, Sahelanthropus tchadensis, discovered at TM 266, in the Djurab Erg, northern Chad, by the Mission Paléoanthropologique Franco-Tchadienne (2, 3) (MPFT). Their stated intention was to describe ‘the events surrounding the discoveries themselves’ (1) (p. 142), although Beauvilain has already done so at length (4). Their contribution in the South African Journal of Science alleges that : 1) Vignaud et al. (3) failed to present correctly the stratigraphic nature of the hominid site TM266 ; 2) Brunet et al. (2) neglected collected hominid specimens ; 3) the mandibular specimen TM266-02-154-1 described by Brunet et al. (2) is in fact a fossil hominid chimera manufactured by a left m/3 incorrectly glued to a right hemimandible ; 4) together, these supposed errors affect the Minimum Number of Individuals (MNI) count for the site. Beauvilain and Le Guellec (1) do not question the attribution of the fossil to the hominid clade (2) rather than to an African ape, but attempt to show that the MPFT members reached inaccurate conclusions. The team firmly stands by its original statements.
Geological issues
Given the thorough geological survey performed by the MPFT in the Djurab since 1994, including georadar investigations (3, 5, 10), it is clear that the whole Toros-Menalla (TM) fossiliferous area shows no evidence whatsoever of a faulting during at least the last 7 Myr. Except for the modern dunes, the entire landscape is very flat. In the TM area, all of the small scarps pointed out by Beauvilain and Le Guellec (1) are the consequences of aeolian ‘over-digging’ at the foot of the dunes, as are very common across the Sahara and in many other sandy deserts.
These geomorphological features do not in our view represent any ‘reactivated ancient faulting’ as they allege (p. 142). The section given in Vignaud et al. (3) is synthetic, showing the different encountered facies related to the alternation of humid and dry periods. The section at TM 266 is accurate as published, and all fossil specimens reported in references (2) and (3) were derived from this local section as published therein. There is no doubt about their provenance.
Inventory issues
The MPFT practices of inventorying and publishing fossils does not differ from those normally practised in palaeontology. All collected specimens, including hominids, are registered under an inventory number comprising the name of the site, the year, a specimen number, and, in the case of several pieces of the same individual, a part number (e.g. the cranium nicknamed ‘Toumaï’ was numbered TM266-01-060-1). This attribution of an inventory number occurs at different stages when processing the discoveries : 1) for most of them, directly in the field after a precise identification; 2) in the laboratory (at N’djamena or Poitiers) for all the specimens recovered after sieving, or after cleaning for some specimens completely embedded in matrix. Beauvilain, a geographer in charge of MPFT logistics, was unfamiliar with this process and the way in which specimens were assembled into the published hypodigm of S. tchadensis (2).
The first paper describing the new taxon S. tchadensis (2) included only the specimens which were definitively identified as hominid by their anatomical characters. These specimens belong to several individuals, as we reported in Nature (2) : the holotype cranium is one of these specimens. Beauvilain and Le Guellec (1) wonder why a very worn incisor (TM266-01-460) and a damaged partial mandibular symphysis (TM266-02-203) were not included in the paratype series. They were not included because their exact affinities are yet to be fully developed and determined. Further studies of more fragmentary remains have identified additional individuals, and the MNI count will expand as both excavations and preparation work continue.
Issues of restoration and interpretation
In the Djurab desert, the discovery of fossils is facilitated by an intense erosion of the sediments in which they are embedded through the action of the sand blown by winds across the sedimentary units. When the fossils are unearthed, the same aeolian erosion also affects them. The damage mostly consists of polishing, cracking, breaking, dispersion of the different parts, and, finally, total destruction of the specimens if they are not collected almost immediately after their first exposure. For example, the cranium TM266-01-060-1 of Sahelanthropus tchadensis was partially unearthed when found and had suffered from such a weathering by sandblasting. During its exposure, it lost most of its front teeth. As reported in Beauvilain and Le Guellec, the broken right canine belonging to this skull was found separately. There is no doubt that this canine belonged to this cranium, because, as correctly noted by Beauvilain and Le Guellec (1) (p. 143): ‘The tooth consisted of two fragments which fitted perfectly onto the right canine root’. However, they erroneously reported it as a ‘complete’ canine whereas in fact it is the distal half of the canine. This canine was published in its natural position on the cranium (2).
A parallel case occurred for the mandible in question. The right third molar had been displaced from the tooth row by erosion and transported by wind to where it was recovered, some decimetres distant from the mandible with the remaining teeth. After recovery, we established that it belonged to the mandible itself, and we attached it where it belonged, as a right m/3 of the hemi-mandible TM266-02-154-1. Beauvilain and Le Guellec now assert that this tooth has been attributed to and mounted on the incorrect side. This moderately worn tooth bears substantial occlusal anatomy which unambiguously identifies it as a third molar. The identification of the side was based on two decisive independent criteria, one set physical and the other set biological. First, there is an unambiguous match between the lower surface of the tooth and its roots, which remained in the mandible. There is no doubt about the integrity of this join (Fig. 1A, B, C, F, G). This is further confirmed by the matching interproximal facet preserved on the mesial surface of the tooth in question and the second molar retained by the mandible. Second, the anatomy of the third molar allows unambiguous siding. As in all hominoid teeth, the buccal cusps are the more worn, with a larger, most heavily worn cusp (the protoconid), marked here by heaviest occlusion and placed mesiobuccally (Fig. 1D, E). The occlusal rims of the lingual cusps stand out slightly but distinctly, from less wear due to well-known masticatory mechanisms common to modern humans, fossil hominids, and fossil and modern apes.
Fig. 1. Right hemi-mandible TM266-02-154-1 of Sahelanthropus tchadensis. A, B, and C: CT scans (courtesy: University Museum, University of Tokyo) at the level of the m/3. The mandibular corpus and the retained roots of the m/3 are in light red. The crown of the third lower molar found separately and claimed to be a left side is in blue. A precise matching between the m/3 crown and the corresponding roots in the hemi-mandible can be observed.
The interstitial space between the m/3 and its roots corresponds to thickness of the glue used to affix the tooth to its roots.
A, Sagittal sections with mesial side at right from right to left, CT scans are respectively shot at 3.33 mm, 4.41 mm, 7.83 mm, and 8.70mm from the buccal edge of the tooth ;
B, transversal sections with lingual side at right from right to left, CTscans are respectively shot at 2.67 mm, 3.69 mm, 4.11 mm, and 9.36mm from the mesial edge of the tooth ;
C, sections parallel to the occlusal surface, at the cervix level and below, with mesial side at top from right to left, CT scans are respectively shot at 6.93 mm, 7.14 mm, 7.44 mm, and 7.80mm from the occlusal edge of the tooth. Mesially, the mesio-buccal and mesio-lingual roots remaining in the corpus (see F) appear in light red and show exact matching with the m/3 crown (in blue) ;
D, occlusal view of the complete specimen with its m/3 ;
E: occlusal view of the m/3 ;
F: occlusal view of the m/3 roots ;
G, disto-lingual view of the join (white arrow) between the m/3 and its distal root.
All scale bars are 0.5 mm.
Conclusion
The logistical contributions of Beauvilain to the fieldwork in Chad are gratefully acknowledged, but the claims and assertions by him and Le Guellec (1) have no bearing on either the interpretation of the geology of TM 266 or of the associations, taxonomy, or phylogeny of Sahelanthropus tchadensis.
We thank the Chadian authorities (Ministère de l’Education Nationale, de l’Enseignement Supérieur et de la Recherche, Université de N’djamena, CNAR).
We extend gratitude for their support to the French ministries, Ministère français de l’Education Nationale (Faculté des Sciences, Université de Poitiers), Ministère de la Recherche (CNRS : SDV & ECLIPSE), Ministère des Affaires Etrangères (DCSUR, Paris and SCAC N’djamena), to the Région Poitou-Charentes, to the RHOI (F.C. Howell and T.D. White) funded by the NSF and also to the Armée Française, MAM and Epervier, for logistic support.We specially thank G. Suwa (University Museum, University of Tokyo) for the CT scans, and C.O. Lovejoy and T.D. White for stimulating discussions. We especially thank also all the other MPFT members who joined us for the field missions, G. Florent, C. Noël and Sabine Riffaut for administrative and technical supports.
Bibliography
1. Beauvilain A. and Le Guellec Y. (2004). Further details concerning fossils attributed to Sahelanthropus tchadensis (Toumaï). S. Afr. J. Sci. 100, 142-144.
2. Brunet M., Guy F., Pilbeam D., Mackaye H.T., Likius A., Ahounta D., Beauvilain A., Blondel C., BocherensH., Boisserie J-R., Bonis L. de, Coppens Y., Dejax J., Denys C., Duringer P., Eisenmann V., Fanoné G., Fronty P., Geraads D., Lehmann T., Lihoreau F., Louchart A., Mahamat A., Merceron G., Mouchelin G., Otero O., Pelaez Campomanes P., Ponce De Leon M., Rage J-C., Sapanet M., Schuster M., Sudre J., Tassy P., Valentin X., Vignaud P., Viriot L., Zazzo A. and Zollikofer C.(2002). A new hominid from the Upper Miocene of Chad, Central Africa. Nature 418, 145-151.
3. Vignaud P., Duringer P., Mackaye H.T., Likius A., Blondel C., Boisserie J-R., Bonis L. de, Eisenmann V., Etienne M-E., Geraads D., Guy F., Lehmann T., Lihoreau F., Lopez-Martinez N., Mourer- Chauviré C., Otero O., Rage J-C., Schuster M., Viriot L., Zazzo A. and Brunet M. (2002). Geology and palaeontology of the Upper Miocene Toros-Menalla hominid locality, Chad. Nature 418, 152-155.
4. Beauvilain A. (2003). Toumaï, l’aventure humaine. La Table Ronde, Paris.
5. Brunet M., Beauvilain A., Coppens Y., Heintz E., Moutaye A.H.E. and Pilbeam D. (1995). The first australopithecine 2500 kilometres west of the Rift Valley ( Chad). Nature 378, 273274.
6. Brunet M., Beauvilain A., Geraads D., Guy F., Kasser M., Mackaye H.T., Maclatchy L.M., Mouchelin G., Sudre J. and Vignaud P. (1998). Tchad: découverte d’une faune de Mammifères du pliocène inférieur. C. R. Acad. Sci. Paris 326, 153-158.
7. Brunet M. and M.P.F.T. (2000). Chad: discovery of a vertebrate fauna close to the Mio-Pliocene boundary. J. Vert. Paleont. 20(1), 205-209.
8. Schuster M. (2002). Sédimentologie et paléoécologie des séries à vertébrés du paléolac Tchad depuis le Miocène supérieur. Ph.D. thesis, Université Louis Pasteur, Strasbourg.
9. Ghienne J.M., Schuster M., Bernard A., Duringer Ph. and Brunet M. (2001). The Holocene giant Lake Chad revealed by digital elevation models. Quat. Int. 87, 81-85
10. Schuster M., Duringer Ph., Ghienne J.F., Beauvilain A., Mackaye H.T., Vignaud P. and Brunet M. (2003). Discovery of coastal conglomerates around the Hadjer El Khamis Inselbergs (Western Chad, Central Africa): a new evidence for lake Mega-Chad episodes. The Costal conglomerates of Lake Mega-Chad. Earth Surf. Proc. Landf. 28(10), 1059-1069.
†Jean-Renaud Boisserie a,b, Djimdoumalbaye Ahounta c, Cécile Blondel a, Louis de Bonis a, Yves Coppens d, Christiane Denys e, Philippe Duringer f, Véra Eisenmann e, Pierre Fronty a, Denis Geraads g, Gongdibé Fanoné c, Franck Guy a,k, Thomas Lehmann a, Fabrice Lihoreau a,h, Andossa Likius h, Antoine Louchart i, Hassane Taisso Mackaye h, Olga Otero a, Pablo Pelaez Campomanes j, David Pilbeam k, Marcia Ponce De Leon l, Jean-Claude Rage e, Mathieu Schuster f, Pascal Tassy e, Xavier Valentin a, Patrick Vignaud a, Laurent Viriot a and Christoph Zollikofer l.
a CNRS UMR 6046, Université de Poitiers, 40 Avenue du Recteur Pineau, 86022 Poitiers Cedex, France;
b Laboratory for Human Evolutionary Studies, University of California, 3060 Valley Life Sciences Building, Berkeley, CA 94720,U.S.A.;
c Centre National d’Appui la Recherche, BP 1228, N’Djaména, Tchad;
d Collège de France, place Marcellin Berthelot, 75005 Paris, France;
e Muséum National d’Histoire Naturelle et CNRS UMR 8569, rue Cuvier, 75005 Paris, France;
f CNRSUMR7517, Université Louis Pasteur, 1 rue Blessig, 67084 Strasbourg, France;
g CNRS UPR 2147, 44 rue de l’Amiral Mouchez, 75014 Paris, France;
h Université de N’Djaména, BP 1117, N’Djaména, Tchad;
i CNRS UMR 5125, Université Claude Bernard, 2743 Bd du 11 novembre 1918, 69622 Villeurbanne, France;
j Museo de Ciencias Naturales, C/Guttierez Abascal 2, 28006 Madrid, Spain;
kPeabody Museum, Harvard University, 11 Divinity Avenue, Cambridge, MA 02138, U.S.A.;
lAnthropologisches Institut/Multimedia Laboratorium, Universität Zürich-Irchel, Winterthurer Str. 190, 8057 Zürich, Switzerland.
'LETTRE INTERNATIONALE DE SOUTIEN'
(in italics Press release diffused in November 2004)
July 1, 2004
Dr. Graham Baker
Editor
South African Journal of Science
Dear Graham,
A recent paper published in the South African Journal of Science has put into question the identity of a unique and important Chadian hominid fossil and the competence of the team that described it in Nature.
Attached you will find a comment that we and a set of professional paleoanthropologists wish to publish in your journal to set the record straight about the correct identification of the specimen in question. All of our coauthors were sent the Beauvilain and Le Guellec SAJS article via pdf, along with j-pegs of CT images and detailed photographs of the tooth in question (artificially isolated from the mandible so that its siding would be judged exclusively on the basis of crown morphology). The e-mail that we sent to these colleagues on June 22 is reproduced below.
As you will see, to date, we have 27 coauthors from 13 countries, all offering unequivocal support for the identification of the tooth as from the right side. Many of these coauthors provided anatomical justification for their identifications, and several expressed surprise about how this article passed through the review process into print without being questioned.
We understand that Professor Brunet is providing an independent response to Beauvilain and Le Guellec, and we hope that our contribution might be published alongside this and the apology that Dr. Martin Pickford has sent you by e-mail.
With all best wishes,
F . Clark Howell Tim D. White
Sir, – We, the undersigned, have carefully examined the photographs and digital crown images of a fossilized third molar from the upper Miocene of Chad. This tooth was originally identified by the discoverers (Brunet et al. 2002, Nature 418, 145151) as a right third mandibular molar. Arecent paper by Beauvilain and Le Guellec (2004, S. Afr. J. Sci. 100, 142144) claimed that this tooth had been misidentified and was in fact a left lower third molar. Based on crown anatomy evident in the images examined by us, we confirm the identity of this tooth as a right molar, as originally published by Brunet et al. (2002).
F. Clark Howell, Laboratory for Human Evolutionary Studies, Museum of Vertebrate Zoology, The University of California at Berkeley, Berkeley, CA 94720, U.S.A. E-mail: fchlhes@socrates.berkeley.edu
Tim D. White, Laboratory for Human Evolutionary Studies, Museum of Vertebrate Zoology and Department of Integrative Biology, The University of California at Berkeley, Berkeley, CA 94720, U.S.A. E-mail: timwhite@socrates.berkeley.edu
David R. Begun, Department of Anthropology, University of Toronto, Toronto, ON M5S 3G3, Canada. E-mail: begun@chass.utoronto.ca
Yaowalak Chaimanee, Paleontology Section, Bureau of Geological Survey, Department of Mineral Resources, Rama VI Road, Bangkok 10400, Thailand. E-mail: yaowalak@dmr.go.th
Marie-Antoinette de Lumley, Institut de Paléontologie Humaine, 75013 Paris, France. E-mail: prehist@mnhn.fr
Philip D. Gingerich, Museum of Paleontology, University of Michigan, Ann Arbor, MI 48109-1079, U.S.A. E-mail: gingeric@umich.edu
Colin Groves, School of Archaeology and Anthropology, Australian National University, Canberra, A.C.T. 0200, Australia. E-mail: colin.groves@anu.edu.au
Erksin Güleç, Department of Physical Anthropology and Paleoanthropology, University of Ankara, 06100, Sihhiye, Ankara, Turkey. E-mail: erksin.gulec@humanity.ankara.edu.tr
Yohannes Haile-Selassie, Cleveland Museum of Natural History, 1 Wade Oval Drive, Cleveland, OH 44106, U.S.A. E-mail: yhailese@cmnh.org
Leslea Hlusko, Department of Integrative Biology, The University of California at Berkeley, Berkeley, CA 94720, U.S.A. E-mail: hlusko@socrates.berkeley.edu
Jean-Jacques Jaeger, Equipe Phylogénie, Paléobiologie & Paléontologie, I.S.E.M., CNRS-Université Montpellier II, UMR 5554, Cc 064 Place Eugéne Bataillon, 34095 Montpellier Cedex 5, France. E-mail: jaeger@isem.univ-montp2.fr
Jay Kelley, Department of Oral Biology, College of Dentistry, University of Illinois at Chicago, Chicago, IL 60612, U.S.A. E-mail: jkelley@uic.edu
Meike Köhler, Institute de Paleontologia M. Crusafont, c/ Escola Industrial 23, 08201 Sabadell, Barcelona, Spain. E-mail: kohlerlm@diba.es
Wu Liu, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China. E-mail: liuwu@ivpp.ac.cn
David Lordkipanidze, Georgian State Museum, 0105 Tbilisi, Georgia. E-mail: geonathist@ip.osgf.ge
C. Owen Lovejoy, Matthew Ferrini Institute for Human Evolutionary Research, Department of Anthropology, Kent State University, Kent, OH 44242, U.S.A. E-mail: olovejoy@aol.com
Lawrence B. Martin Department of Anthropology and of Anatomical Sciences, The Graduate School, Stony Brook University, NY 11794-4433, U.S.A. E-mail: lawrence.martin@stonybrook.edu
Monte L. McCrossin, Department of Sociology and Anthropology, MSC 3BV, New Mexico State University, P.O. Box 30001, Las Cruces, NM 88003-8001, U.S.A. E-mail: mmccross@nmsu.edu
Jacopo Moggi-Cecchi, Laboratori di Antropologia, Dipartimento di Biologia Animale e Genetica, Universitá di Firenze, via del Proconsolo 12, 50122 Firenze, Italy. E-mail: jacopo@unifi.it
Salvador Moyà-Solà, Institute de Paleontologia M. Crusafont, c/ Escola Industrial 23, 08201 Sabadell, Barcelona, Spain. E-mail:moyass@diba.es
Lorenzo Rook, Dipartimento di Scienze della Terra, Università di Firenze, via G. La Pira, 4, 50121 Firenze, Italy. E-mail: Lrook@geo.unifi.it
Pat Smith, Department of Anatomy, The Hebrew University Hadassah Medical School, Jerusalem, Israel. E-mail: pat@cc.huji.ac.il
Gen Suwa, The University Museum, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan. E-mail: suwa@um.u-tokyo.ac.jp
Mark Teaford, Center for Functional Anatomy and Evolution, Johns Hopkins University School of Medicine, Baltimore, MD 21205, U.S.A. E-mail: mteaford@jhmi.edu
Phillip V. Tobias, School of Anatomical Sciences, University of the Witwatersrand, Johannesburg, South Africa. E-mail: tobiaspv@anatomy.wits.ac.za
Alan Walker, Departments of Anthropology and Biology, The Pennsylvania State University, University Park, PA 16802, U.S.A. E-mail: axw8@psu.edu
Phil Walker, Department of Anthropology, The University of California at Santa Barbara, Santa Barbara, CA 93106, U.S.A. E-mail: pwalker@anth.ucsb.edu
Steven Ward, Department of Anatomy, NEOUCOM, Rootstown, OH 44272- 0095, U.S.A. E-mail: scw@neoucom.edu