CHAPTER 9: HOMININ ORIGINS (PGS.

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1 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

2 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 smallerbodied 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

3 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 ( mya) Australopiths diverse forms, some more primitive, others highly derived ( mya) Early Homo the first members of our genus ( mya) Pre-Australopiths ( 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 lower premolar, with the wear leading to honing of the surfaces of both teeth. This anatomical pattern is typical of most Old World anthropoids, but is mostly absent in hominins Paleoanthropologists have placed the Toros-Menalla remains into a new genus and species of hominin, Sahelanthropus tchadensis 3/6

4 o The dating is only approximate, based on biostratigraphic correlation with sites in Kenya o It is difficult to see how Sahelanthropus could be anything but hominin The position of its foramn magnum is intermediate between that of a quadrupedal ape and that of a bipedal hominin suggesting that this time, ape may be a better classification for Sahelanthropus Probably living around the same time as the Sahelanthropus, two other very early (possible) hominin genera have been found at sites in central Kenya Australopiths ( mya) Australopiths a colloquial name referring to a diverse group of Plio-Pleistocene African hominins. Australopiths are the most abundant and widely distributed of all early hominins and are also the most completely studied. There are two major subgroups of australopiths, an earlier one that is more anatomically primitive and a later on that is much more derived Major features that all australopiths share: o They are all clearly bipedal (although not necessarily identical to Homo in this regard) o They all have relatively small brains (at least compared to Homo) o They all have large teeth, particularly the back teeth, with thick to very thick enamel on the molars o Are relatively small-brained, big-toothed bipedals Researchers say that Australopithecus anamensis has the potential to be the ancestor for many later australopiths as well as early members of the genus Homo Australopithecus afarensis Complex remains of Australopithecus have come primarily from the sites of Hadar (in Ethiopia) and Laetoli (in Tanzania) Some researchers have concluded that A. afarensis was not bipedal in quite the same way modern human are A. afarensis share more primitive features with late Miocene apes with living great apes than do later hominins, who display more derived characteristics The teeth of A. afarensis are quite primitive canines are often lage, pointed teeth Cranial capacity estimates for A. afarensis show a mixed pattern when compared with alter hominins The upper limbs are longer than in modern humans the wrist, hand and foot bones show several difference from modern human From the abundant limb bones recovered A. afarensis walked bipedally when on the ground These hominins were also clearly obligate bipeds, which would have hampered their climbing abilities but would not necessariy have precluded arboreal behavior altogether Later More Derived Australopiths ( mya) There were three separate lineages of hominins living between 2.0 and 1.2 mya The most derived australopiths are the various members of Paranthropus Paranthropus have the biggest teeth of all, especially as seen in its huge premolars The Paranthropus face is faltter than that of any other australopth and a ridge develops on the top of the skull called the sagittal crest Saggital Crest a ridge of bone that runs down the middle of the cranium like a short Mohawk. This serves as the attachment for the large temporal muscles, indicating strong chewing New Connections: A Transitional Australopith? Researchers have assumed that Homo probably first evolved in Africa Australopith-like characteristics seen in A. sediba include a small brain, long arms with curved fingers and several primitive traits in the feet A. sediba most resembles its potential immediate South African predecessor A. africanus (even when sediba was said to be from 2mya) Some other aspects of A. sediba more resemble Homo. 4/6

5 Closer Connections: Early Homo ( mya) The earliest appearance of genus Homo in East Africa may date back well before 2 mya Plio-Pleistocene pertaining to the Pliocene and first half of the Pleistocene, a time range of 5-1 mya. For this time period, numerous fossil hominins have been found in Africa There have been more than one species of Homo living in Africa during the Plio-Pleistocene The Homo habilis material at Olduvai dates to about 1.8 mya, but due to the gragmentary nature of the fossil remains, evolutionary interpretations have been difficult The naming of the fossil material as Homo habilis ( handy man ) was meaningful from two perspectives o This group were the early Olduvai toolmakers o At least two separate branches of hominin evolution in the Plio-Pleistocene With a cranial capacity of 775cm3, this individual is well outside the known range for australopiths and actually overlaps the lower boundary for later species of Homo The shape of the skull vault is in many respects unlike that of australopiths however, the face is still quite robust At least one species (and possibility two) of early Homo was present in East Africa perhaps a little prior to 2 mya, developing a parallel with an australopith species These hominin lines lived contemporaneously for a minimum of 1 million year, after which time the australopiths apparently disappeared forever One lineage of early Homo likely evoled into H. erectus about 1.8 mya Any other species of early Homo became extinct sometime after 1.4 mya The Lower Paleolithic Period: Emergence of Human Culture Acheulian Pertaining to a stone tool industry from the Early and Middle Pleistocene; characterized by a large proportion of bifacial tools (flaked on both sides). Acheulian tool kits are common in Africa, southwest Asia, and Western Europe, but they re thought to be less common elsewhere. The name Oldowan was coined decades ago by Louis and Mary Leakey to describe early stone tools and archaeological sites found at Olduvai Gorge, Tanzania These Oldowan assemblages demonstrate that by 2.6 mya, hominins were already inventing and adopting cultural, rather than purely biological Oldowan tools are extremely rudimentary compared with the simplest known modern human technology Hard Hammer Percussion a direct percussion method of making stone tools that uses one rock as a hammer to knock flakes from another rock that serves as a core Oldowan tools were expedient tools, meaning that they tended to be made when they were needed, used and then discarded Oldowan tools are properly viewed as the oldest tools that archaeologists can reliably identify Lower Paleolithic hominins are best described as tool-assisted gatherers and meat scavengers Interpretations: What Does it all Mean? Selecting and surveying sites Excavating sites and recovering fossil hominins Designating individual finds with specimen numbers for clear reference Cleaning, preparing, studying and describing fossils Comparing with other fossil material in a chronological framework if possible Comparing fossil variation with known ranges of variation in closely related groups of living primates and analyzing ancestral and derived characteristics Assigning taxonomic names to fossil material Seeing the Big Picture: Adaptive Patterns of Early African Hominins Speciation was occurring quite frequently among the varous lineages of early homininsmore frequently than among later hominins 5/6

6 Early hominin species (pre-australopiths, Asutralopithecus, Paranthropus, and early Homo) all has restricted ranges o Each hominin species exploited a relatively small area and could easily have become separated from other populations of its own species Most of these species appear to be at least partially tied to arboreal habitats o Paranthropus was probably somewhat less arboreal than Ardipithecus or Australopithecus Except for some early Homo individuals there s very little in the way of an evolutionary trend of increased body size or of markedly greater encephalization All of these early African hominins show an accelerated developmental pattern, on quite different from the delayed developmental pattern characteristic of Homo sapiens Summary of Main Topics The earliest very primitive primates evolved in the Paleocene around 65 mya Many primate fossil forms more similar to living primates evolved in the Eocene (56-36 mya). Most of these species went extinct, although some show connections to modern lemurs/lorises or to tarsiers The first anthropoids probably date to the late Eocene, but are much better documented from the Fayum Oligocene site (about 33 mya) Large-bodied hominoids are wide-spread ad diverse in the Old World throughout the entire Miocene (23-5 mya) The first hominins appear 7-6 mya, and for the next 5 million years are all restricted to Africa Many species of these early African hominins have been identified and can be summarized within three major subgroups: (1) Pre-australopiths ( mya) including three genera of very early, and still primitive (possible) hominins:sahelanthropus, Orrorin, and Ardipithecus (2) Australopiths ( mya) early, more primitive ausstralopiths species ( mya), including Australopithecus anamensis and Australopithecus afarensis. Later, more derived australopith species ( mya), including two genera: Paranthropus and a later species of Australopithecus (3) Early Homo ( mya) the first members of our genus, who around 2 mya likely diverged into more than one species The earliest known stone tools date to about 2.6 mya, but cut marks on bones and other evidence suggest that hominins were perhaps tool users more than 3.3 mya Hominin tool use was such a fundamental change that our subsequent evolution turned in a completely new direction to one that is both biological and cultural. It also marked the beginning of the archaeological record 6/6

NOTES: Ch 34 - Mammals & Primate / Human Evolution ( )

NOTES: Ch 34 - Mammals & Primate / Human Evolution (34.7-34.8) Class: MAMMALIA Mammals possess unique derived characteristics: 1) Provide young with milk (mammary glands) 2) Internal fertilization; some