Chapter 8 Hominid Origins - Cengage

Chapter 8 Hominid Origins - Cengage

Chapter 10 Paleoanthropology: Reconstructing Early Hominid Behavior and Ecology Chapter Outline Definition of Hominid The Strategy of Paleoanthropology Paleoanthropology in ActionOlduvai

Gorge Dating Methods Excavations at Olduvai Chapter Outline Experimental Archaeology Reconstruction of Early Hominid Environments and Behavior Issue: The Piltdown Caper: Whodunit?

Definition of Hominid The earliest evidence of hominids dates to the end of the Miocene and includes dental and cranial pieces. Modern humans, as well as our most immediate hominid ancestors, are distinguished from the great apes by more obvious features than tooth and jaw dimensions.

Mosaic Evolution A pattern of evolution in which the rates of evolution in one functional system vary from those in other systems. For example, in hominid evolution, the dental system, locomotor system, and neurological system (especially the brain) all evolved at markedly different rates. Culture

Extrasomatic (non-bodily) adaptations to the environment. This includes systematic learned behaviors that can be communicated to others. Aspects of this capacity have been identified among our closest ape relatives. Mosaic Evolution

of Hominid Characteristics Locomotion Modern Homo sapiens Bipedal: shortened pelvis; body size larger; legs longer; fingers and toes not as long Early hominid Bipedal: shortened pelvis; differences from later hominids, smaller body size and long arms relative to legs; long fingers and toes; probably capable of considerable climbing

Miocene, generalized hominoid Quadrupedal: long pelvis; some capable of considerable arm swinging, suspensory locomotion Mosaic Evolution of Hominid Characteristics Brain Modern Homo sapiens

Greatly increased brain sizehighly encephalized Early hominid Larger than Miocene forms, moderately encephalized; prior to 6 m.y.a., no more encephalized than chimpanzees Miocene, generalized hominoid

Small compared to hominids, but large compared to other primates; a fair degree of encephalization Mosaic Evolution of Hominid Characteristics Dentition Modern Homo sapiens Small incisors; canines further reduced; molar tooth enamel caps thick Early hominid

Moderately large incisors; canines somewhat reduced; molar tooth enamel caps very thick Miocene, generalized hominoid Large front teeth (including canines); molar teeth variable, depending on species; some have thin enamel caps, others thick enamel caps Mosaic Evolution

of Hominid Characteristics Toolmaking Behavior Modern Homo sapiens Stone tools found after 2.5 m.y.a.; increasing trend of cultural dependency apparent in later hominids Early hominid In earliest stages unknown; no stone tool use prior to 2.5 m.y.a.; more oriented toward tool manufacture and use than chimpanzees

Miocene, generalized hominoid Unknownno stone tools; probably had capabilities similar to chimpanzees Paleoanthropology Paleoanthropology is 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. Subdisciplines of Paleoanthropology Physical Sciences Biological Sciences

Social Sciences Geology Physical anthropology Archaeology Geomorphology Ecology

Ethnoarchaeology Geophysics Primatology Cultural anthropology Chemistry Taphonomy Psychology Multidisciplinary

Refers to research involving mutual contributions and cooperation of experts from various scientific fields (i.e., disciplines). Artifacts Objects or materials made or modified for use by hominids. The earliest artifacts are usually made of

stone or, occasionally, bone. Taphonomy The study of how bones and other materials came to be buried in the earth and preserved as fossils. Taphonomists study the processes of sedimentation, the action of streams, preservation properties of bone, and carnivore disturbance factors.

Context The environmental setting where an archaeological trace is found. Primary context is the setting in which the archaeological trace was originally deposited. A secondary context is one to which it has been moved (such as by the action of a

stream). 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.

Zinjanthropus Zinjanthropus cranium, discovered by Mary Leakey at Olduvai Gorge in 1959. This fossil is now included as part of the genus

Paranthropus. The Main Gorge at Olduvai Olduvai Gorge Geological processes make Olduvai extremely important to paleoanthropological investigation: Faulting exposes geological beds near the surface. Active volcanic processes cause rapid sedimentation which preserves bone and artifacts.

Volcanic activity provides a wealth of radiometrically datable material. 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 and Chronometric Dating Examples Relative Dating Chronometric Dating Stratigraphy Fluorine Dating K/Ar Radiocarbon (14 C)

Fission-track Steady decay of Provides a sequence; radioactive isotope Methodological i.e., no estimates in provides estimate in basis actual number of years actual number of years 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. Thermoluminiscence Technique for dating certain

archaeological materials, such as stone tools, heated in the past, that release stored energy of radioactive decay as light upon reheating. Question The dating technique for dating stone tools heated in the past that release stored energy of radioactive decay as light upon reheating is: a) radiocarbon (C-14). b) thermoluminiscence.

c) stratigraphy. d) fission-track. Answer: b The dating technique for dating stone tools heated in the past that release stored energy of radioactive decay as light upon reheating is thermoluminiscence. Question

You want to cross-check a site in Africa that has been dated by K/Ar. You have found a fossilized pig skeleton. Which dating technique can be used to help date this site? a) fluorine dating b) biostratigraphy c) dendrochronology d) paleomagnetism Answer: b You want to cross-check a site in Africa

that has been dated by K/Ar. You have found a fossilized pig skeleton. The biostratigraphy dating technique can be used to help date this site. Principle of Superposition In a stratigraphic sequence, the lower layers were deposited before the upper layers. Half-life

The time period in which one half the amount of a radioactive isotope is converted chemically (into a daughter product). For example, after 1.25 billion years, half the 40K remains; after 2.5 billion years, one-fourth remains. Excavations in Progress at Olduvai

This site, more than 1 million years old, was located when a hominid ulna (arm bone) was found eroding out of the side of the gorge. Data From Oluvai Grouped into categories: 1. Butchering localities, areas containing one or a few individuals of a species of large mammal associated with a scatter of archaeological traces. 2. Quarry localities where early hominids extracted stone to make tools.

3. Multipurpose localities, areas where hominids ate, slept, and put the finishing touches on their tools. Remains at Olduvai A dense scatter of stone and some fossilized animal bone from a site at Olduvai, dated at

approximately 1.6 mya. Some of these remains are the result of hominid activities. Stone Tool (Lithic) Technology

When struck properly, certain types of stone will fracture in a controlled way; these nodules are called blanks. The smaller piece that comes off is called a flake, while the larger remaining chunk is called a core. Both core and flake have sharp edges useful for cutting, sawing, or scraping. The earliest hominid cultural inventions probably used materials that didnt survive. Flake and Core Direct Percussion

Pressure Flaking Microwear The polish left on an experimental flint implement after scraping wood for 10 minutes.

Bright, smooth areas are the microwear polish; dark, grainy areas are the unworn flint surface. Arrows indicate implement edge. Environmental Determinism An interpretation that links simple environmental changes directly to a major

evolutionary shift in an organism. Such explanations tend to oversimplify the evolutionary process. Stable Carbon Isotopes Isotopes of carbon that are produced in plants in differing proportions, depending on environmental conditions. By analyzing the proportions of the isotopes contained in fossil remains of

animals (who ate the plants), its possible to reconstruct aspects of ancient environments. Factors Influencing the Initial Evolution of Bipedal Locomotion Factor Speculated Influence Carrying Upright posture freed the arms to carry various objects.

Hunting Systematic hunting is now thought not to have been practiced until after the origin of bipedal hominids. Seed and nut gathering Feeding on seeds and nuts occurred while standing upright. Factors Influencing the Initial

Evolution of Bipedal Locomotion Factor Speculated Influence Feeding from bushes Upright posture provided access to seeds, berries, etc., in lower branches; analogous to adaptation seen in some specialized antelope. Thermoregulation (cooling) Vertical posture exposes less of the body to direct sun; increased distance from

ground facilitates cooling by increased exposure to breezes. Factors Influencing the Initial Evolution of Bipedal Locomotion Factor Speculated Influence Visual surveillance Standing up provided better view of surrounding countryside (view of potential

predators as well as other group members). Long-distance walking Covering long distances was more efficient for a biped. Male Provisioning Males carried back resources to dependent females and young.

Factors Influencing the Initial Evolution of Bipedal Locomotion Factor Speculated Influence Carrying Upright posture freed the arms to carry various objects. Hunting Systematic hunting is now thought not to have

been practiced until after the origin of bipedal hominids. Seed and nut Feeding on seeds and nuts occurred while gathering standing upright. 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 curvesa backward (thoracic) one and a forward (lumbar) onethat keep the trunk (and weight) centered above the pelvis.

Question Which of the following is not one of the reasons offered as an explanation for why hominids initially became bipedal? a) carrying objects b) foraging c) eating seeds and nuts d) walking long distance Answer: b

Foraging is not one of the reasons offered as an explanation for why hominids initially became bipedal.

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