sign in sign up
<<
Home , Chororapithecus, Sahelanthropus, Sivapithecus

of is a holdover from a gradistic approach to phylogeny. Future discoveries of infra-cranial material to determine locomotor abilities are of utmost importance. If S. tchadensis is shown to be a biped, then bipedalism arose soon after the divergence point, and much earlier than anticipated. Some caution should be taken, as the mosaic features of S. tchadensis could be evidence of a complicated evolutionary history during the supposed divergence period. Genetic evidence now points to a period of hybridization, which would make sorting out the affiliation of purported hominin fossils problematic. For the present, it appears that S. tchadensis can be classified as the first known hominin. tchadensis: AN Even if future finds cause a re-evaluation of EXAMINATION OF ITS HOMININ its phylogenetic status, S. tchadensis is a AFFINITIES AND POSSIBLE valuable addition to the fossil record. PHYLOGENETIC PLACEMENT Knowledge of early panin morphology is also essential to phylogenetic relationships of early hominins.

Abstract WHAT IS A HOMININ? An examination of the Sahelanthropus tchadensis is a Sahelanthropus tchadensis material supports candidate for the first known hominin.1 Its its putative hominin status. The cranial age, at nearly seven million--old morphology of S. tchadensis exhibits a (Vignaud et al. 2002: 155), places it very mosaic of primitive and derived close to the supposed divergence point of characteristics. This is to be expected from a the and lineages (Wood species so near to the assumed divergence 2002: 133). A hominin is a member of the point of the chimpanzee and human , which include any species lineages. However, the of the that are found upon the that ultimately derived characteristics align it closer to the lead to sapiens (Wood 2005: 23). hominin clade than to the panin clade. While Similarly panins are members of the Tribe it cannot be shown conclusively that S. tchadensis was an obligate biped, evidence from a recent virtual-reconstruction is Note that all the literature cited still uses the indicative of an upright posture. However, term hominid, which is reflective of a more the status of the earliest hominin should not traditional . For the purpose of rest entirely on the presence of an upright this paper the meaning are equivalent, as form of locomotion. It should not be Brunet et aI., refer to a hominid as "any expected that the first members of the member of that group more closely related hominin clade would necessarily have a to extant than to the extant completely bipedal mode of locomotion. ," (2002: 753). Attributing hominin status solely on the

TOTEM: vo1.l6 2007-2008 Panini, which include any species that are of abyssinicus, so far found upon the clade that leads to Pan represented only by nine individual teeth, troglodytes (Wood 2005: 23). This there were no known fossils from this represents current taxonomical thinking, time period (Suwa et al. 2007: 921). To which stresses cladistic taxonomy, or sorting ascertain the appearance of the first out evolutionary relationships based on hominin, it will be necessary to know the derived characteristics. Unfortunately little morphology of early members of the panin is currently known about Upper lineage as well. This will allow the in general, which are ancestral to these determination of which traits are primitive two lineages (Suwa et al. 2007:921).This Upper Miocene ape characteristics, versus compounds the problem of identifying the which are derived hominin characteristics. It earliest hominin in the fossil record. As the must be remembered that the last common divergence point is approached, it becomes ancestor of the hominin and panin lineages increasingly more difficult to identify to would not resemble an extant chimpanzee. which of these a fossil should be Using extant chimpanzees to sort out assigned (Fleagle 2000: 96). It may be primitive versus derived traits is ultimately impossible to ever identify the problematic, as chimpanzees have been last common ancestor of the chimpanzee and evolving ever since the divergence point. human lineages with any certainty. With the problems of homoplasies and Evolution is mosaic in nature. Traits reversals in evolution, fossils of early panins do not necessarily evolve at the same rate in are sorely needed. a lineage. Among the hominins, the evolution of bipedalism preceded brain Sahelanthropus tchadensis CRANIAL encephalization by at least two million MORPHOLOGY years, and given recent possible hominin The holotype for S. tchadensis is TM discoveries such as S. tchadensis, up to five 266-01-060-1, a 95% complete million years. One must thus be cautious in cranium(Brunet et al. 2002a: 146). TM 266 attributing hominin status based on single is the Toros-Menalla fossil locality, located traits or fragmentary fossils. The story of in the Djurab Desert of , 2500 km west Ramapithecus and its past hominin status, from the supposed origin of previously one that was based mostly on thick known hominins in east (Brunet et al. enamel and supposedly reduced canine teeth 2002a: 146). While the cranium is virtually highlight this problem (pilbeam 1966: 1). complete, it suffers from severe However unlike Ramapithecus, S. deformation. It was found in one piece, with tchadensis is known from a virtually matrix filled cracks. The cranium features a complete cranium as well as multiple mosaic of primitive and derived traits. The mandibular fragments (Brunet et al. 2005: face in particular is derived from that of 752). With more information available, one Upper Miocene apes since it is short in should be able to make a more accurate length and presents with a marked reduction attribution of S. tchadensis's phylogenetic in facial prognathism. The cranium placement. however, is very primitive and ape like. It is The problem of recognizing the first long and has a small cranial capacity, hominin is compounded by the dearth of initially estimated to be between 320-380cc fossils in the Upper Miocene of Africa, based on the original distorted cranium especially the period between five and seven (Brunet et al. 2002a: 146), and revised to million years ago. Until the recent discovery 370-380cc based on CT scans and a virtual

TOTEM: vo1.16 2007-2008 Copyright © 2008 TOTEM: The U.W.O. Journal of Anthropology reconstruction of the cranium (Zollikofer et cannot be obtained through faunal al. 2005: 758). correlation due to differences in faunal The cranium is best described as migration rates, there appears to be no derived anteriorly and primitive posteriorly. controversy in the literature regarding the According to Wood, "put simply, from the dating of TM 266 locality. Thus, S. back it looks like a chimpanzee, whereas tchadensis is currently the oldest candidate from the front it could pass for a 1.75- for hominin status. million--old advanced australopith" (2002: 134). While it shares its derived face Sex Determination with that of later hominins, S. tchadensis Determining the sex of the S. presents with a supraorbital torus that is tchadensis cranium is of great importance, unlike any seen in early hominins. It has a as its hominin status may vary depending on thick and flat continuous brow similar to whether one ascribes it as a male or a female those found in . This of course of its species. In many apes, males exhibit does not imply any phylogenetic substantial in body size, relationship (Wolpoff et al. 2002: 581). The robusticity, and musculature, especially of brows are relatively larger, and absolutely the mastication apparatus. Even species thicker, than those of male , yet the exhibiting less body dimorphism between cranium is diminutive in size, similar to that the sexes still possess marked sexual of a female chimpanzee (Brunet et al. dimorphism in the canines, such as the 2002a: 148). The canines feature apical wear extant . Male apes in particular have or are worn down on the tips (Brunet et al. a marked canine/pre-molar honing complex, 2002a: 150). The holotype was found where the distal edge of the maxillary canine without a mandible, but other mandibular hones against the mesial edge of the fragments, as well as numerous teeth, have mandibular third pre-molar. This results in a been recovered from adjacent areas. cut back, or angled mesial surface to the pre- Unfortunately no lower third pre-molar has molar . Female apes are conversely yet been recovered. This tooth is of more gracile in body size and robusticity, importance because it forms part of the have reduced canines and often lack a robust canine/pre-molar honing complex, a honing complex (Wolpoff et al. 2002: 581). primitive feature of Upper Miocene apes, Interpretation of the sex of S. but one that is lacking in known hominins tchadensis is complicated by the mosaic (Brunet et al. 2005: 753). nature of the cranial features. It simply does not fit neatly among known apes analogues. Dating The cranium is very robust. It has a massive The fossils have been dated to supraorbital torus. It presents with a large between six and seven million-years-old nuchal crest and a large and rough nuchal (Vignaud et al. 2002: 155) with recent plane, indicative of large neck musculature. analysis favouring a date closer to seven Based on robustness alone, the S. tchadensis million (Brunet et al. 2005: 753). This cranium could be sexed as a male (Brunet et makes S. tchadensis the oldest of the al. 2002a: 148). potential hominins uncovered thus far. Based on the canines, and indirectly, Dating of the TM 266 locality was done based on cranial size, S. tchadensis could through faunal correlation with two sites in instead be sexed as a female. The canines Kenya: Lukeino, and Lothagam (Vignaud et are much reduced in size, and they lack a al. 2002: 152). These sites are dated significantly honed distal edge. The crowns radiometrically, and while an absolute date are small, and there is no evidence of a

TOTEM: vo1.16 2007-2008 diastema in the teeth (Brunet et ai. 2005: interpretation of S. tchadensis being either a 754). These are also characteristics are female hominin or male apes. Might this not indicative of a female apes. The small be an example of one's paradigm canines combined with a small cranial size influencing the interpretation of data? Those could lead to a sexing of the cranium as a claiming that the cranium is female also female (Wolpoff et al. 2002: 581). claim that canine teeth are the best indicator Regardless of which sex the fossil is of sex in a cranium (Wolpoff et al. 2002: attributed to, anomalies arise that need to be 581). However if only the canine was used explained. If female, one must explain the to sex crania, then all early hominins must high degree of robusticity in the cranium, have their sex reattributed as female. At especially in the brows, which is unlike any some point in the evolutionary history of the seen in a female chimpanzee (Brunet et aI., hominins, a species must exist that began to 2002b: 582). It would also follow that male exhibit canine reduction. When this occurs, S. tchadensis specimens would be even and what cranial or infra-cranial more robust in their cranial features. The morphology accompanies this canine male would undoubtedly be one of the more reduction, is open to question. At the same robust apes yet discovered, especially for its time one must be cautious, as early size. Recall that for a cranium the size of a interpretations of possible hominins, most female chimpanzee, S. tchadensis has brows notably Ramapithecus, were based mostly larger than a male . on canine size and lack of a diastema, or the If the cranium is male, one needs to shape of the dental arcade (pilbeam 1966: explain the reduction of the canines, lack of 1). The Ramapithecus has now been a diastema and reduction of facial sunk, and the fossils have been subsumed as prognathism. This is easily done if S. female members of the genus , tchadensis is placed on the hominin lineage. a ape species which exhibited marked sexual All of the above are derived features that are dimorphism (Wolpoff et al. 2002: 581). As found among later hominins. Ascribing the noted, unlike the hominin descriptions of sex as male appears to be the more Ramapithecus, S. tchadensis is known from parsimonious explanation. Note that here an almost complete cranium, one with very are two testable scientific hypotheses, and robust and hominin like characteristics. future fossil finds should be able to Until further evidence comes to light, the determine which one is correct. If for description of the S. tchadensis cranium as example, a larger and more robust cranium male seems appropriate. However, it is is discovered or even featuring large important to remember how sex sexually dimorphic canines and a marked determination can vastly alter any canine/pre-molar honing complex is phylogenetic interpretations. uncovered, it would be clear that TM 266- 01-060-1 was a female, and its hominin Canine Morphology status would rightly need to be reconsidered. The canines of S. tchadensis are It is interesting to note that those reduced, in that they feature small crowns who were quick to label S. tchadensis as but still retain very long tooth roots (Brunet nothing but an ape, describe it as a female et ai. 2005: 753). The canines also feature a (Wolpoff et al. 2002: 581), while those high degree of apical wear, meaning they are calling it the earliest known hominin worn down on the apex of the tooth (Brunet describe it as a male (Brunet et al. 2002b: et al. 2005: 753). There is some exposure of 582). I have not come across an dentin along the distal edge of the canine crown, but there is not a sharp honed distal

TOTEM: vo1.16 2007-2008 Copyright © 2008 TOTEM: The U.W.O. Journal of Anthropology edge (Brunet et ai. 2005: 754). In known relaxation of selection pressure for large apes, both fossil and extant, canines canines, but rather a positive selection typically have large crowns and a sharp against them. If reduction only resulted from continuous honed distal edge (Brunet et at. relaxation of selection pressures for large 2002a: 146). The canine teeth are primarily canines, it could be supposed that crown and used for slicing in apes. Apes also lack root reduction would occur symmetrically. apical wear on the canine tips (Begun 2004: The fact that the molars feature low cusps 1479). However, apical wear is a feature of (Brunet et at. 2002: 146) suggestive of a diet hominin canines, whose jaws did much requiring grinding and chewing action, this more lateral grinding and chewing 0Nood also lends weight to the argument that 2002: 134). Crown size aside, the wear dietary needs were influencing the canine features of S. tchadensis canines is more reduction. It has long been believed in similar to those of hominins (Brunet et at. that the emergence of 2002b: 582).It must be noted that in hominins included a shift in dietary describing phylogenetic relationships, gross strategies from those of arboreal apes 0Nood morphology can be misleading. Only 2002: 134). Evidence of this is found in S. specific, derived traits should be considered tchadensis. when determining evolutionary relationships. Based on canine morphology Enamel Thickness in relation to a male sex attribution, S. The enamel thickness of the tchadensis can thus be placed in the hominin posterior dentition is intermediate between clade. the chimpanzees and the Surprisingly, little has been made of (Brunet et at. 2002a: 150). This would be the relation of the size of the expected in an early hominin near the crown, to the tooth root. I speculate that this chimpanzee and human divergence point. is an intermediate form of canine reduction, One must still keep in the mosaic or another example of mosaic evolution. It nature of evolution, and remember that might be assumed that canine tooth characteristics do not always evolve at the reduction would be scalar, featuring a same rate. Critics again recalled the use of similar reduction in both crown and root. In enamel thickness to ascribe hominin status S. tchadensis there is retention of a long root to Ramapithecus (Wolpoff et ai. 2002: 581). with a reduced crown (Brunet et at. 2005: In ape evolutionary history, there has been a 753).This implies not only selection pressure pattern of reversals in enamel thickness, and on canine reduction, but a differential it is probably true that enamel thickness selection pressure between tooth crown and alone cannot be used as an indicator of root. If the ability to grind or chew foods phylogenetic relationships. Not having early was part of the dietary package of S. chimpanzee fossils as of yet, it is unknown tchadensis (Wood 2002: 134), it is not if enamel thickness was indeed thin in the surprising that selection pressure would be last common ancestor of the panin and most positive on the crowns of the teeth. hominin lineages (Begun 2004: 1479). Reduction of roots would follow at a later One needs to be cautious of reversals time. and homoplasies in enamel thickness. There The reduction of crown size would was significant variation in enamel thickness also imply that there was a positive selection among Upper Miocene apes, and even more pressure on canine reduction as a whole. problematic, a complete lack of certainty of Canine reduction did not result from a phylogenetic relationships among these apes, let alone which one was ancestral to

TOTEM: vo1.16 2007-2008 TOTEM: The U.W.O. Journal of Anthropology the later hominins (Fleagle 2000: 96). Thus, Both researchers achieved similar an early hominin could have had thin or results.The face appears to be somewhat thick molar enamel, theoretically.If the last more lengthened, and there is an increase in common ancestor of panins and hominins the prognathism of the lower face, as the had an intermediate enamel thickness, then original fossil was distorted in this area intermediate enamel thickness in S. (Zollikofer et al. 2005: 756). However, the tchadensis is a symplesiomorphy, and it is reconstructed cranium as a whole appeared indicative of nothing. This is a specific to look more like a hominin than does the example of the need for finding more fossil original, the gross morphology is more panins in particular. While many discoveries similar to an than that of a of Upper Miocene apes have recently been chimpanzee. Clearly any reconstruction is made, there still seems to be a bias towards open to interpretation, but reconstructions of the importance of hominin fossils, both in shattered crania have long been the norm in the popular media, and in paleoanthropology (Gorder 2005: 12). Most paleoanthropology. known fossil crania are physical reconstructions, often pieced together from VIRTUAL-RECONSTRUCTION multiple shattered fragments. So to treat a While 95% complete, the cranium of computer reconstruction with more S. tchadensis presents with severe plastic consternation than a physical reconstruction distortion.The face is flattened and twisted, would be unfair. If done properly, a virtual- and the cranial base is also twisted and reconstruction should be both theoretically compressed (Zollikofer et al. 2005: 755). more accurate than a physical one (Gorder These deformations have affected the tooth 2005: 13), and allow for easy dissemination rows significantly, and to a lesser extent, the of information to other scientists position and orientation of the foramen electronically, avoiding the problems of magnum. In order to compensate for the access to fossils that plagues the discipline distortion, a virtual-reconstruction of the of paleo anthropology (Gorder 2005: 13). Of cranium was attempted by Zollikofer et al. course the best confirmation of the (2005: 755). CT scans of the cranium were reconstruction would be if an independent taken, and the data were then manipulated team verified the results, based on a separate using computer software. Their goal was to reconstruction. While Zollikofer and Ponce reconstruct the original morphology de Leon claim not to have any bias towards (Zollikofer et al. 2005: 755). The original the outcome of the reconstruction, they have cranium was analysed to determine which been affiliated with Brunet, the discoverer of parts were filled with matrix. The cranium S. tchadensis since the original description was then 'disassembled' along the original of the fossils (Zollikofer et al. 2005: 755). cracks and any matrix filling was removed. Undistorted cranial fragments were used to EVIDENCE FOR BIPELDALISM mirror and replace damaged sections The virtual-reconstruction also (Zollikofer et al. 2005: 755). The 'pieces' addressed the question of bipedalism in S. were then manipulated back into shape. To tchadensis. In the initial description, the minimize bias, researchers at two separate authors were careful not to address the work stations completed separate question of bipedalism (Brunet et al. 2002a: reconstructions and the studies were done in 151).They attributed its hominin status blind. The two researchers did not compare based on cranial morphology, and were any findings until completion of the much more cautious than others to attribute reconstruction (Zollikofer et al. 2005: 755). obligate bipedalism based on slim or newly

TOTEM: vo1.16 2007-2008 Copyright © 2008 TOTEM: The U.W.O. Journal of Anthropology discovered fossil evidence (Senut et al. angles of the . Even if 2001: 137).Three years later, and with the some error was taken into account, S. aid of the virtual-reconstruction, Zollikofer tchadensis would still comfortably fit in the et al. were ready to make the suggestion that hominin range. In order to obtain a ape like S. tchadensis was a biped (Zollikofer et al. orientation, the reconstruction would have to 2005: 756). At the very least, they were have been grossly flawed. unable to preclude the possibility of However if the data is taken at face bipedalism. value, one could speculate that S. tchadensis Lacking infra-cranial material, the was actually more advanced in its locomotor relative position and angle of the foramen abilities than the much later A. magnum are the best indicators of africanus.While this may seem unlikely for bipedalism. It should be pointed out that a hominin so close to the divergence point even in the distorted cranium the foramen with a presumed quadrupedal common magnum is more anteriorly located than in a ancestor, there has been a debate recently as chimpanzee, where the foramen magnum is to whether the genus almost completely towards the rear of the actually played any role in the evolution of cranium (Brunet et al. 2002a: 151). the genus Homo (Senut 1996: 39).This is the However, it is not positioned as far forward exact hypothesis put forward recently in as it is in later hominins. It should not be support of bipedalism in tugenensis unexpected that an intermediate or (Senut et al. 2001: 142). Senut had transitional location of the foramen magnum previously argued that a very early biped would exist during the course of early gave rise to the genus Homo, and the hominin evolution. majority of the australopithecines lay on a In an upright biped, the angle side branch (Senut 1996: 39). between the foramen magnum and the According to Zollikofer et al. (2005: orbital plane is roughly 90 degrees 755), there is also evidence of bipedalism in (Zollikofer et al. 2005: 757). In other words, S. tchadensis at an extremely early date. It is the foramen magnum lies in a plane ironic then, that Senut and Pickford were horizontal to the ground and the plane of the two of the authors quick to discount any orbits is vertically oriented. However, this possible hominin affiliation of S. tchadensis angle varies between bipedal hominins and (Wolpoff et al. 2002: 582). Yet the same quadrupedal apes. In quadrupedal apes, this authors had no problem ascribing obligate angle is much more acute. In S. tchadensis bipedalism to their own putative first the planes through the foramen magnum and hominin, 0. tugenensis (Senut 2001: 137). the orbits also meet at a near right angle. S. In fact, in their critique of S. tchadensis, tchadensis is thus more akin to they mention an unnamed " Australopithecus africanus than to P. penecontemporary with a perfect troglodytes, and in fact it has the greatest and well-developed post cranial adaptation affinity with H sapiens (Zollikofer et al. to obligate bipedalism is more likely to have 2005: 758). been an early hominin" (Wolpoff et al. The extreme affinity of the 2002: 582). This of course would be 0. orientation of the foramen magnum in S. tugenensis, although no mention is made of tchadensis with that of H sapiens could the controversies of its hominin status, perhaps be interpreted as a flaw in the which is based mostly on the fragmented virtual-reconstruction. It is possible that the proximal end of a femur (Senut 2001: 137). reconstruction slightly exaggerated the This is not the most reliable indicator of

TOTEM: vo1.l6 2007-2008 2008 TOTEM: The V.W.O. Journal of Anthropology hominin status, the distal femur which is not The hybridization model claims that after an present in this case, being more indicative of initial divergence seven million-years-ago, bipedalism (Brunet et al. 2002b: 582). roughly a million years of hybridization One last speculation on S. tchadensis occurred between the panin and the hominin relates to the large nuchal crest and lineages (Patterson et al. 2006: 1106). If not presumed presence of heavy neck a hominin, S. tchadensis could neither be musculature. If S. tchadensis was a bipedal classified as an early panin. A mosaic of hominin, with a foramen magnum sitting hominin and panin traits would show up under the cranium, why the heavy neck during this hybridization period. Also note musculature? I propose it is possible that in that as hominins should not be defined a transitional form of biped, lacking a fully solely by the adaptation to bipedalism, it is forward-oriented foramen magnum, and possible that Upper Miocene apes could enlarged neck muscles were retained to have in fact been bipedal, and yet not balance the cranium horizontally on the hominins. This also dovetails with another cranium. Note that in the species recent hypothesis that suggests the ancestors Australopithecus aethiopicus which featured of hominins were not knuckle-walkers, a rather posteriorly located foramen which is anatomically a highly derived form magnum, and an extremely large nuchal of locomotion, but in fact were upright or crest, no question of its obligate bipedalism orthogonal, suspensory apes (Thorpe et al. has been raised, nor has anyone questioned 2007: 1330). The morphology of S. its hominin attribution. This is mentioned tchadensis conforms to these two only to keep in mind that unexpected forms hypotheses-that hybrids should be found that of bipedalism and unusual morphologies feature both hominin and panin may be found near the initial adaptive characteristics, and that early hominin radiation of the hominins. ancestors were descended from apes that had Based on the virtual-reconstruction, an upright posture. bipedalism may indeed have been present in S. tchadensis. This is a significant finding CONCLUSIONS for two reasons. First, if S. tchadensis was S. tchadensis is currently a likely bipedal, bipedalism arose very early in candidate for title of the earliest hominin. evolution. Second, if S. tchadensis is found Its age is appropriate, although in light of a not to be a hominin, but nonetheless bipedal, recent genetic study it may possibly be too then this suggests that the evolution of old. However, genetic based phylogenies bipedalism was not a unique event, which in appear to be overturned as often as fossil and of itself would be a surprising based phylogenies. The mosaic nature of discovery. derived and primitive characteristics in S. tchadensis are to be expected in an early GENETICS AND HYBRIDIZATION hominin. With a lack of Upper Miocene ape, The phylogenetic placement of S. and early hominin fossils for comparison, tchadensis is further complicated by a recent knowing exactly which traits to look for to hypothesis proposing a potential period of be primitive versus which would be derived hybridization between the human and is problematic. The hominin status of S. chimpanzee lineages (patterson et al. 2006: tchadensis should always be open to 1106). The study forwards the notion that revision, especially in the light of new data. such a period occurred exactly during the It is reckless to attribute hominin status time of S. tchadensis. If this bears out, then based on a single characteristic, or S. tchadensis could not be an early hominin. fragmentary fossils.

TOTEM: vo1.16 2007-2008 Copyright © 2008 TOTEM: The U.W.O. Journal of Anthropology With the discovery S. tchadensis we Campomanes, Marcia Ponce de Leon, Jean- have a nearly complete cranium dating back Claude Rage, Michel Sapanet, Mathieu seven million-years ago, which presents Schuster, Jean Sudre, Pascal Tassy, Xavier with multiple derived hominin traits. These Valentin, Patrick Vignaud, Laurent Viroit, include the reduction of the canine teeth, Antoine Zazzo, and Christoph Zollikofer. intermediate thickness of tooth enamel, and 2002a. A New Hominid from the Upper the position of the foramen magnum, which Miocene of Chad, Central Africa. Nature. is indicative of a biped. Having 418: 801-808. interconnecting lines of evidence strengthens S. tchadensis's placement on the Brunet, Michel, Franck Guy, David hominin clade. If a period of hybridization Pilbeam, Hassane T. Mackaye, Andossa did occur near the divergence of humans and Likius, Djimdoumalbaye Ahounta, Alain chimpanzees, then S. tchadensis exhibits an Beauvilain, Cecile Blondel, Herve example of the mosaic morphology one Bocherensk, Jean-Renaud Boisserie, Louis would expect. However there is no reason to De Bonis, Yves Coppens, Jean Dejax, exclude S. tchadensis from the hominin Christiane Denys, Philippe Duringer, Vera clade at the current time. Regardless of its Eisenmann, Gongdibe Fanone, Pierre ultimate affinity, its discovery is of no less Fronty, Denis Geraads, Thomas Lehmann, importance to hominin and primate Fabrice Lihoreau, Antoine Louchart, Adoum evolution as a whole. Mahamat, Gildas Merceron, Guy Mouchelin, Olga Otero, Pablo P. Campomanes, Marcia Ponce de Leon, Jean- Claude Rage, Michel Sapanet, Mathieu Begun, David R. 2004. The Earliest Schuster, Jean Sudre, Pascal Tassy, Xavier Hominid-Is Less More? Science. 303: 1478- Valentin, Patrick Vignaud, Laurent Viroit, 1480. Antoine Zazzo, and Christoph Zollikofer. 2002b. Reply to Sahelanthropus or Brunet, Michel, Franck Guy, David 'Sahelpithecus'? Nature. 419: 582. Pilbeam, Daniel E. Lieberman, Andossa Likius, Hassane T. Mackaye, Marcia S. Fleagle, John G. 2000. The Century of the Ponce de Leon, Christoph P. E. Zollikofer, Past: One Hundred Years in the Study of and Patrick Vignaud. 2005. New material Primate Evolution. Evolutionary of the earliest hominid from the Upper Anthropology. 9(2): 87-100. Miocene of Chad. Nature. 434: 752-755. Gorder, Pam F. 2005. Tournai: Reverse- Brunet, Michel, Franck Guy, David Engineering a Human Ancestor. Computing Pilbeam, Hassane T. Mackaye, Andossa in Science and Engineering. July/August 05: Likius, Djimdoumalbaye Ahounta, Alain 10-23. Beauvilain, Cecile Blondel, Herve Bocherensk, Jean-Renaud Boisserie, Louis Patterson, Nick, Daniel 1. Richter, Sante De Bonis, Yves Coppens, Jean Dejax, Gnerre, Eric S. Lander, and David Reich. Christiane Denys, Philippe Duringer, Vera 2006. Genetic evidence for complex Eisenmann, Gongdibe Fanone, Pierre speciation of humans and chimpanzees. Fronty, Denis Geraads, Thomas Lehmann, Nature. 441: 1103-1108. Fabrice Lihoreau, Antoine Louchart, Adoum Mahamat, Gildas Merceron, Guy Mouchelin, Olga Otero, Pablo P.

TOTEM: vo1.16 2007-2008 2008 TOTEM: The U.W.O. Journal of Anthropology Pilbeam, David. 1966. Notes on Wood, Bernard. 2002. Hominid revelations Ramapithecus the earliest known hominid, from Chad. Nature. 418: 133-135. and . American Journal of Physical Anthropology. 25: 1-6. Wood, Bernard. 2005. : A Very Short Introduction. Oxford: Oxford Senut, Brigitte, Martin Pickford, Dominique University Press. Gommery, Pierre Mein, Kiptalam Cheboi, and Yves Coppens. 2001. First hominid Zollikofer, Christoph P. E., Marcia S. Ponce from the Miocene (Lukeino Formation, de Leon, Daniel E. Lieberman, Franck Guy, Kenya). C. R. Acad. Sci. Paris. 332: 137- David Pi1beam, Andossa Likius, Hassane T. 144. Mackaye, Patrick Vignaud, and Michel Brunet. 2005. Virtual cranial reconstruction Senut, Brigitte. 1996. systematics of Sahelanthropus tchadensis. Nature. 434: and phylogeny. South African Journal of 755-759. Science. 92(4): 165-166.

Suwa, Gen, Reiko T. Kono, Shigehiro Katoh, Berhane Asfaw, and Yonas Beyene. 2007. A new species of great ape from the late Miocene epoch in Ethiopia. Nature. 448: 921-925.

Thorpe, S. K. S., R. L. Holder, and R. H. Crompton. 2007. Origin of Human Bipedalism as an Adaptation for Locomotion on Flexible Branches. Science. 316: 73-76.

Vignaud, Patrick, Philippe Duringer, Hassane T. Mackaye, Andossa Likius, Cecile Blondel, Jean-Renaud Boisserie, Louis de Bonis, Vera Eisenmann, Marie- Esther Etienne, Denis Geraads, Franck Guy, Thomas Lehmann, Fabrice Lihoreau, Nieves Lopez-Martinez, Cecile Morer-Chauvire, Olga Otero, Jean-Claude Rage, Mathieu Schuster, Laurent Viriot, Antoine Zazzo, and Michel Brunet. 2002. Geology and palaeontology of the Upper Miocene Torros- Menalla hominid locality, Chad. Nature. 418: 152-155.

Wolpoff, Milford H., Brigitte Senut, Martin Pickford, and John Hawks. 2002. Sahelanthropus or 'Sahelpithecus'? Nature. 419: 581-582.

TOTEM: vo1.l6 2007-2008 Copyright © 2008 TOTEM: The U.W.O. Journal of Anthropology