The History of Our Tribe Hominini Textbook Part II Miocene Epoch Chapter 6 Sahelanthropus tchadensis

PART II EPOCH THE EPOCH ( Figure , on this side of the pond North . by Jay is in the public domain . Relative to the Epoch , the was initially warmer and by the , primates had once again ventured into the northern latitudes . This time they were apes , versus the of the . However , like those earlier primates , the northern apes would eventually go extinct due to global cooling that began . Whenever there is climatic change , floral and faunal changes follow . Much of the dense equatorial forests became more open , and grasslands and deserts expanded so that the African landscape became more of a mosaic environment , versus deep , dark jungle . Initially the apes were very successful at diversifying and expanding into new niches as mentioned in Chapter , this was the time of the hominoid adaptive ation . Over time , however , as the landscape continued to change and forests became increasingly , the majority of ape species went extinct , leaving only a handful of species in Africa . In recent years , three new genera of have been discovered in Africa . While there is debate as to whether the oldest , is a true , and are generally accepted as true . Caution must be exercised in the interpretation of the fossil record . It is tempting to formulate a linear history for our species , species A gave rise to Species which gave rise to Species , etc . The fossil record is extremely incomplete and we may get only a glimpse of the species that lived at a particular time and place . are continually revising their theories as new discoveries are made and old material is reinterpreted in light of new discoveries , and working hypotheses . 57

. human from the I Chad ) Figure by Taylor .

Figure Cast of the cranium . us . by is licensed under . SITES , Chad PEOPLE Michel Brunet INTRODUCTION The specimen ( see Figure ) was discovered in 2001 at the site of , in the Desert of northern Chad , by Michel Brunet and associates . Brunet incredible quest for in that area is documented in the NOVA series , Becoming Human ( nova evolution ) The species name translates to human from the of Chad . The is the region of dry grasslands south of the Sahara desert . The skull has been nicknamed in the language , meaning hope of life . The location of the fossil material came as a surprise in that only one species of had ever been discovered west of the Great Rift Valley of East Africa , see Chapter 12 ) 60 The History of Our Tribe

20 11 , Tu ul im 20 an ( can ?

wry mo ac uc av 10 20 Figure Toros site , Chad . 266 location by 120 is in the public domain . However in 1998 , Noel speculated that , contrary to the Rift theory for the origin of the , a of the ancestral stock that gave rise to the chimp and human lineages became isolated in a riparian ( riverine or gallery ) forest zone in Chad that was surrounded by arid , open land . At a later point in time , a forest corridor allowed their movement into East Africa . Part of the problem at that point in was that no species of , prior to the , had been discovered in East Africa . They seemingly appeared de 110120 in the fossil record , beginning about , with no intervening stages or missing links in evidence . We now have much older species from Kenya and Ethiopia , and , respectively . PHYLOGENY While the phylogeny of is unknown , some researchers believe that it may represent a stem or basal , ie . one of the earliest members of our tribal tree . Note Once a genus is used the first time in a document , it can subsequently be abbreviated . Just as we do not know the ancestry of the species , we do not have any species that are good contenders for its descendants . 61

DISCOVERY AND GEOGRAPHIC RANGE As mentioned , the holotype ( the fossil ( from a particular individual that are assigned to and used to define the characteristics of a species ) was discovered at the desert site of Toros ( see Figure ) Unless fossils are discovered elsewhere , it is impossible to speculate about the extent of the geographic range of the species . Figure of by Elisabeth . PHYSICAL CHARACTERISTICS The skull of is very robust , with a brain and pronounced muscle . While only fragmentary material has been discovered , some researchers claim that the foramen magnum is anteriorly oriented , suggesting an upright and bipedal . Pronounced brow ridges are also concordant with early status . The facial profile is surprisingly orthognathic and the jaws lack the honing complex , leading some researchers to speculate that may lie near the base of our family tree , versus other phylogenetic scenarios . However , the pronounced posterior neck attachments have led others to suggest that may have been quadrupedal . ENVIRONMENT AND WAY OF LIFE Based upon fossilized faunal remains at the site , such as freshwater fish , rodents , and monkeys , it is likely that inhabited a forest environment in close proximity to an ancient lake ( Wayman 2012 ) Their way of life was likely that of a ape . Like ( see Chapter ) their molar enamel was thinner than that of the later and they thus likely had a diet consisting of fruit , young leaves , and tender shoots . 62 The History of Our Tribe