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Chapter 9

Textbook Chapter 9 Notes

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Heather Miller

Notes From Reading CHAPTER 9:H OMININO RIGINS(PGS. 197-230) Learning Objectives  Explain the general time depth for the earliest primates and explain how they may (or not) be related to living primates  Define what a “hominin” is and explain what sort of evidence is used to determine whether a fossil form is a hominin  Describe the time depth and geographical location of early hominins and explain how they relate to later hominins (including us) Introduction  Hominins evolved from earlier primates (dating back to almost 50 mya)  Paleoanthropologists have made many exciting discoveries from several sites in Africa  The earliest members of the human family were confined to Africa  Much later their descendants disperse from the African continent to other areas of the Old World Early Primate Evolution  The earliest primates evolved from early and still primitive placental mammals  The earliest primates date to the Paleocene (65-66 mya) and belong to a large and diverse group of primitive mammals called the plesiadapforms Ecocene Primates: Closer Connections to Living Primates  A vast number of fossil primates have ben discovered and now total more than 200 recognized species  Darwininus was meant to make a big splash, yet virtually no other experts in early primate evolution have had an opportunity to see the original fossil  Looking at this entire array of Eocene fossils, it is certain that they were (1) primates, (2) widely distributed, and (3) mostly extinct by the end of the Eocene  Most of the Eocene primates (including Darwininus) don’t appear to have been ancestral to any later primate, and they became extinct before the end of the Eocene  New evidence of Eocene anthropoid origins has recently been discovered at a few sites in North Africa  The earliest anthropoids first evolved in Africa Oligocene Primates: Anthropoid Connections  The Oligocene (33-32 mya) has yielded numerous additional fossil remains of several different early anthropoid species  By the early Oligocene, continental drift had separated the New World from the Old World  Late in the Eocene or very early in the Oligocene, the first anthropoids (primitive “monkeys”) arose in Africa and later reached South America by “rafting” over the water separation  Postcranial – referring to all or part of the skeleton not including the skull. The term originates from the fact that in quadrupeds, the body is in back of the head; the term literally means “behind the head”  Apidium may lie near or even before the evolutionary divergence of Old and New World anthropoids  The genus Aegyptopithecus is represented by several well-preserved crania and abundant jaws and teeth  Aegyptopithecus is a very primitive Old World anthropoid, with a small brain and long snout and not showing any derived features of either Old World monkeys or hominoids  It may be close to the ancestry of both major groups of living Old World anthropoids  Aegyptopithecus further suggests that the crucial evolutionary divergence of hominoids from other Old World anthropoids occurred after this time Miocene Fossil Hominoids: Closer Connections to Apes and Humans  In Africa, Asia and Europe, a diverse and highly successful group of hominoids emerged  The Miocene could be called “the golden age of hominoids”  Migrations of animals from Africa directly into southwest Asia became possible  Miocene fossil hominoid assemblage has been interpreted and reinterpreted 1/6 Notes From Reading CHAPTER 9:H OMININ ORIGINS(PGS. 197-230)  Given uncertainty, it is probably best, for the present, to group Miocene hominoids geographically: 1. African Forms (23-14 mya)  Known especially from western Kenya, these include quite generalized, and in many ways primitive, hominoids  Best-known genus is Proconsul  Proconsul closely resembles a monkey  But there are some derived features of the teeth that link proconsul to hominoids 2. European Forms (16-11 mya)  Known from widely scattered localities in France, Spain, Italy, Greece, Austria, Germany and Hungary, most of these forms are quite derived  The best known of these are placed in the genus Dryopithecus  The Greek fossils, called Ouranopithecus, date to 10-9 mya 3. Asian Forms (15-5 mya)  The largest most varied group of Miocene fossil hominids was geographically dispersed from Turkey through India/ Pakistan and east to Lufeng, in southern China  The best-known genus is Sivapithecus and fossil evidence indicates that most of these hominoids were highly derived  Four general points are certain concerning Miocene hominoid fossils: o They are widespread geographically o They are numerous o They span essentially the entirety of the Miocene, with known remains dated between 23 and 6 mya o At present, they are poorly understood  The following conclusions can be drawn: o These are hominoids – more closely related to the ape-human lineage than to Old World monkeys o They are mostly large-bodied hominoids, that is, more connected to the lineages of orangutans, gorillas, chimpanzees, and humans than to smaller- bodied apes o Most of the Miocene species thus far discovered are so derived that they are probably not ancestral to any living form o One lineage that appears well established is Sivapithecus which shows some highly derived facial features similar to the modern orangutan, suggesting a fairly close evolutionary connection o Evidence of definite hominins from the Miocene hasn’t yet been indisputably confirmed. However, exciting recent finds from Kenya, Ethiopia and Chad suggest that hominins diverged sometime in the latter Miocene Understanding our Direct Evolutionary Connections: What’s a Hominin?  Dental remains alone don’t describe the special features of hominins, and they certainly aren’t distinctive of the later stages of human evolution  Not all characteristics developed simultaneously or at the same pace  Mosaic Evolution – a pattern of evolution in which the rate of evolution in one functional system varies from that in other systems. For example, in hominin evolution, the dental system, locomotor system, and neurological system (especially the brain) all evolved at markedly different rates  Bipedal Locomotion – walking on two feet. Walking on two legs is the single most distinctive feature of the hominins  Bipedal locomotion is the only truly reliable indicator that these fossils were indeed hominins  In later stages of hominin evolution, other features, especially those relating to brain development and behavior, become highly significant What’s in a Name?  Members of the human lineage is refered to as hominins (Hominini) 2/6 Notes From Reading CHAPTER 9:H OMININO RIGINS(PGS. 197-230)  The molecular/ genetic data indicate that the African great apes (gorillas, chimpanzees, bonobos) are significantly more closely related to humans than is the orangutan  Chimpanzees and bonobos are more closely connected to humans than gorillas  It further emphasizes the very close evolutionary connections of humans with African ape and most especially with chimpanzees an bonobos  The term hominoid now refers to all great apes and humans together Walking the Walk: The Bipedal Adaptation  All primates show adaptations for erect body posture, and some species are occasionally bipedal  Efficient bipedalism as the primary form of locomotion is seen only in hominins  Bipedal locomotion freed the hands for carrying objects and for making and using tools  Hominins were bipedal for at least 2 million years prior to the first archaeological evidence of tool use  Bipedal walking is an efficient means of covering long distances  When large game hunting came into play further refinements increasing the efficiency of bipedalism may have been favored The Mechanics of Walking on Two Legs  The most dramatic changes are seen in the pelvis  The pelvis is composed of three elements: two hip bones or ossaa coxae, joined at the back to the sacrum  In a quadruped, the ossa coxae are vertically elongated bones positioned along each site of the lower portion of the spine and oriented more or less parallel to it  In hominins, the pelvis is comparatively much shorter and broader and extends around to the side  This helps to stabilize the line of weight transmission in a bipedal posture from the lower back to the hip joint  The foot must act as a stable support instead of a grasping limb  Hominin bipedalism is both habitual and obligate  Habitual Bipedalism – Bipedal locomotion as the form of locomotion shown by hominins most of the time  Obligate Bipedalism – bipedalism as the only form of hominin terrestrial locomotion. Since major anatomical changes in the spine, pelvis, and lower limb are required for bipedal locomotion, once hominins adapted this mode of locomotion, other forms of locomotion on the ground became impossible  After about 4 mya did further adaptations lead to the fully committed form of bipedalism that is seen in hominins, including ourselves Digging for Connections: Early Hominins from Africa  There are three major groups to recognize  Pre-australopiths – the earliest and most primitive (possible) homnins (6.0+ - 4.4 mya)  Australopiths – diverse forms, some more primitive, others highly derived (4.2 - 1.2 mya)  Early Homo – the first members of our genus (2.0+ - 1.4 mya) Pre-Australopiths (6.0+ - 4.4 mya)  The oldest and most surprising of these earliest hominins is represented by a cranium discovered at a central African site called Toros-Menalla in the modern nation of Chad  The braincase is small, estimated to be no larger than a modern chimpanzee, but it is massively built, with huge browridges in front, a crest on top and large muscles attachments  The lower face, being more tucked in under the brain vault is more of a derived feature more commonly expressed in much later hominins  Honing Complex – the shearing of a large upper canine with the first lo
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