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Chapter 8. Hominid Origins. Chapter Outline. Early Primate Evolution Miocene Fossil Hominids Definition of Hominid The Bipedal Adaptation Biocultural Evolution: The Human Capacity for Culture Paleoanthropology as a Multidisciplinary Science. Chapter Outline. Dating Methods
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Chapter 8 Hominid Origins
Chapter Outline • Early Primate Evolution • Miocene Fossil Hominids • Definition of Hominid • The Bipedal Adaptation • Biocultural Evolution: The Human Capacity for Culture • Paleoanthropology as a Multidisciplinary Science
Chapter Outline • Dating Methods • Early Hominids from Africa • Australopithecus from East Africa • Early Homo • South African Hominids • Interpretations: What Does It All Mean?
Early Primate Evolution • The roots of the primate order go back to the beginnings of the placental mammal radiation circa 65 m.y.a. • The earliest primates were diverging from quite early primitive placental mammals. • A vast number of fossil primates from the Eocene (55–34 m.y.a.) have been discovered and now total more than 200 recognized species.
Eocene Primates • Fossil primates from the Eocene display distinctive primate features. • Looking at the whole array of Eocene primates, it is certain that they were: • Primates • Widely distributed • Mostly extinct by the end of the Eocene.
Early Eocene Primates: Features • Chinese fossils dating from the early Eocene (55–45 m.y.a. have three interesting features: • Forward rotation of the eyes, a feature that makes them distinct from the lemur-loris lineage. • The cranium shows small eye sockets, suggesting they may have been diurnal. • They were all apparently extremely small, weighing less than 1 ounce.
Oligocene Primates • The Oligocene (34–23 m.y.a.) yielded fossil remains of several species of early anthropoids. • By the early Oligocene, continental drift had separated the New World from the Old World. • It has been suggested that late in the Eocene or very early in the Oligocene, the first anthropoids arose in Africa and reached South America by “rafting” over the water separation on drifting chunks of vegetation.
Miocene Hominoid Distribution, From Fossils Thus Far Discovered
Miocene Fossil Hominoids • African forms (23–14 m.y.a.) • Especially from western Kenya, these hominoids are, in many ways, primitive. • European forms (16–11 m.y.a.) • From scattered localities in France, Spain, Italy, Greece, Austria, Germany, and Hungary, most are quite derived.
Miocene Fossil Hominoids • Asian forms (16–7 m.y.a.) • The largest and most varied group from Turkey through India/Pakistan and east to southern China, most are highly derived.
Miocene Hominoid Fossils • These are hominoids—more closely related to the ape-human lineage than Old World monkeys. • Mostly large-bodied hominoids, more akin to the lineages of orangutans, gorillas, chimpanzees, and humans than smaller-bodied apes. • Most of the Miocene forms thus far discovered are so derived that they are probably not ancestral to any living form.
Miocene Hominoid Fossils • One lineage that appears well established relates to Sivapithecus from Turkey and Pakistan. This form shows some derived facial features similar to the modern orangutan, suggesting a fairly close evolutionary link. • Evidence of definite hominids from the Miocene has not yet been indisputably confirmed. However, exciting new finds from Kenya, Ethiopia, and Chad (the latter dating as far back as 7 m.y.a.) suggest that hominids diverged sometime in the latter Miocene.
Patterns of Evolution • Mosaic evolution • Evolutionary pattern in which physiological and behavioral systems evolve at different rates. • Biocultural evolution • Biology makes culture possible and developing culture further influences biological evolution.
The Bipedal Adaptation • Efficient bipedalism as the primary form of locomotion is seen only in hominids. • Advantages of bipedalism: • Freed the hands for carrying objects and for making and using tools. • In the bipedal stance, animals have a wider view of the surrounding countryside. • Bipedal walking is an efficient means of covering long distances.
Obligate Bipedalism • Bipedalism as the only form of hominid terrestrial locomotion. • Since major anatomical changes in the spine, pelvis, and lower limb are required for bipedal locomotion, once hominids adapted this mode of locomotion, other forms of locomotion on the ground became impossible.
Major Features of Hominid Bipedalism • The foramen magnum (shown in red) is repositioned farther underneath the skull, so that the head is more or less balanced on the spine (and thus requires less robust neck muscles to hold the head upright).
Major Features of Hominid Bipedalism • The spine has two distinctive curves—a backward (thoracic) one and a forward (lumbar) one—that keep the trunk (and weight) centered above the pelvis.
Major Features of Hominid Bipedalism • The pelvis is shaped more in the form of a basin to support internal organs; moreover, the ossa coxae are shorter and broader, thus stabilizing weight transmission.
Major Features of Hominid Bipedalism • Lower limbs are elongated, as shown by the proportional lengths of various body segments (e.g., in humans the thigh comprises 20% of body height, while in gorillas it comprises only 11%).
Major Features of Hominid Bipedalism • The femur is angled inward, keeping the legs more directly under the body; modified knee anatomy also permits full extension of this joint.
Major Features of Hominid Bipedalism • The big toe is enlarged and brought in line with the other toes; in addition, a distinctive longitudinal arch forms, helping absorb shock and adding propulsive spring.
Paleoanthropology • Paleoanthropology is defined as the study of early humans. • Paleoanthropologists reconstruct the anatomy, behavior, and ecology of our ancestors: • It is a diverse multidisciplinary pursuit seeking to reconstruct every bit of information possible concerning the dating, anatomy, behavior, and ecology of our hominid ancestors.
Dating Methods Paleoanthropologists use two types of dating methods to tell us the age of sites and fossils: • Relative dating determines only whether an object is older or younger than other objects. • Chronometric (absolute) dating provides an estimate of age in years based on radioactive decay.
Relative Dating Techniques • Stratigrapy - based on the law of superposition, that a lower stratum (layer) is older than a higher stratum. • Fluorine analysis applies to buried bones and groundwater seepage. Bones incorporate fluorine during fossilization.
Relative Dating Techniques • Biostratigraphy - related to changes in the dentition of animals. • Paleomagnetism - based on the shifting of the geomagnetic pole.
Chronometric Dating Techniques • The age of an object can be determined by measuring the rate of disintegration: • Potassium/argon (k/Ar) dating involves the decay of potassium into argon gas. K/Ar has a half-life of 1.25 billion years. • Carbon-14 is a radiometric method commonly used by archeologists. Carbon 14 has a half-life of 5730 years.
Position of the Foramen Magnum • (a) a human and (b) a chimpanzee. • Note the more forward position in the human cranium.
Key Very Early Fossil Hominid Discoveries (pre-Australopithecus)
Features of Australopithecus • They are all clearly bipedal (although not necessarily identical to Homo in this regard). • They all have relatively small brains (i.e., at least compared to Homo). • They all have large teeth, particularly the back teeth, with thick to very thick enamel on the molars.
Laetoli • Dated at between 3.5 and 3.7 m.y.a. • Fossilized hominid footprints were found in an ancient volcanic bed. • Despite agreement that these individuals were bipedal, some researchers feel they were not bipedal in the same way as modern humans.
Hadar (Afar Triangle) • Dating suggests a range from 3.9 to 2.3 m.y.a. • Recovered: • "Lucy" an Australopithecus afarensis female, was recovered here. • Group of bones representing 13 individuals, including 4 infants, suggest a social unit died at the same time. • Some stone tools may be 2.5 million years old, making them the oldest cultural evidence yet found.
Koobi Fora (East Lake Turkana) • This site yielded the richest assemblage of Plio-Pleistocene hominids from the African continent. • Most of the hominids date to 1.8 m.y.a., others date back to 3.3 m.y.a. • 150 hominid specimens recovered at Koobi Fora represent at least 100 individuals.
West Turkana • Two important discoveries: • Discovery of a nearly complete 1.6 m.y.a. Homo erectus adolescent. • Discovery of “the black skull”, a well-preserved 2.4 million year old skull which caused a major reevaluation of Plio-Pleistocene evolution.
Olduvai Gorge • Louis and Mary Leakey conducted continuous excavations from the 1930's to early 1980. • Paleontological evidence includes more than 150 species of extinct animals which can provide clues to the ecological conditions of early hominid habitats.
South African Sites • The first australopithecine “the missing link” between apes and humans was discovered at a quarry at Tuang. • As the number of discoveries accumulated, it became clear that the australopithecines were not simply aberrant apes. • The acceptance of the australopithecines as hominids required revision of human evolutionary theory.
Estimated Body Weights and Stature in Plio-Pleistocene Hominids
Steps in Interpreting Homind Evolutionary Events • Selecting and surveying sites. • Excavating sites and recovering fossil hominids. • Designating individual finds with specimen numbers for clear reference. • Cleaning, preparing, studying, and describing fossils.
Steps in Interpreting Homind Evolutionary Events • Comparing with other fossil material—in 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.
Groups of Plio-Pleistocene Hominids • Specimens represent 200 individuals from South Africa and more than 300 from East Africa. • Divided into four broad groupings: • Set I Basal Hominids. • Set II Early Primitive Australopithecus. • Set III Later, more derived Australopithecus. • Set IV Early homo.
Set I. Basal Hominid(4.4 m.y.a.) • The earliest and most primitive remains are those from Aramis. • They have been classified as Ardipithecus ramidus, a different genus from all other Plio-Pleistocene forms.
Set II. Early Primitive Australopithecus, 4.2-3.0 m.y.a.) • The hominids from Laetoli and Hadar are assigned to Australopithecusafarensis. • A. afarensis is so primitive in the majority of dental and cranial features that if it were not for evidence of bipedalism, this primate would not be classified as a hominid.
Set III. Later, More Derived Australopithecus (2.5-1.0 m.y.a.) • Robust Australopithecines • Larger body size • Small cranial capacities • Very large, broad faces • Massive back teeth and lower jaws • Gracile Australopithecines • Different face dentition
