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Lecture 6

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Lakehead University
Anthropology 1032
Trevor Orchard

Macroevolution: Geological Time and the Rise of New Species Macroevolution  “Changes produced only after many generations, such as the appearance of a new species.”  Key process underlying the study of the fossil story of human evolution ◦ i.e. the basis for Paleoanthropology  Also the basis for Classification: ◦ “The ordering of organisms into categories, such as orders, families, and genera, to show evolutionary relationships.” How to classify animals:  Traditional – Evolutionary Systematics ◦ Presumed ancestors and descendants are traced in time by analysis of homologous characteristics.  Homologies – “Similarities between organisms based on descent from a common ancestor.”  Modern Alternative – Cladistics ◦ Also focus on homologies, but emphasizes derived characteristics, and does not examine temporal relationships. ◦ Derived – “Characters that are modified from the ancestral condition and thus diagnostic of particular evolutionary lineages.” versus... ◦ Ancestral (Primitive) – “Characters inherited by a group of organisms from a remote ancestor.”  But, both strive to reconstruct evolutionary relationships ◦ Text uses a combination that identifies clades, but also shows temporal relationships among those clades. ◦ Clade – “Agroup of organisms sharing a common ancestor and all descendants.” Mammal Classification: Kingdom:Animalia  Phylum: Chordata ◦ Subphylum: Vertebrata  Class: Mammalia  Subclass: Prototheria (platypuses, etc.)  Subclass: Metatheria (Marsupial Mammals, mostly found in Australia and surrounding islands)  Subclass: Eutheria (Placental Mammals)  Order: Primates ( including humans) What are Fossils?  Remains of organisms ◦ Organic minerals replaced with minerals that form rock (Mineralization)  May be an impression  Or the hardened remains of an animal’s skeletal structure Fossilization  Typically involves the hard parts of an organism: ◦ Woody tissues of plants ◦ Bones ◦ Teeth ◦ Shells ◦ Horns  Because they are more likely to be preserved in the ground long enough for mineralization to occur  Needs the right conditions to come together to preserve materials long enough for mineralization to occur Paleoanthropology – the study of fossil humans Taphonomy  “The study of how bones and other materials come to be buried in the earth and preserved as fossils.”  Decay & fossilization depend on the burial environment  Diagenesis – physical, chemical, and biological changes affecting a fossil Limitations of the Fossil Record  Snapshot of life in the past  Fossils not preserved in some parts of the world  Not all fossil-bearing sites have been discovered Why Study Fossils?  Show diversity of life in the past  Provide evidence for patterns and rates of evolution  Often show intermediate or primitive forms  Create an ecological and biogeographical context to understand evolution  Provide temporal framework...  Looking for appearance of new animals over time Where Did itAll Begin?:ABrief Evolutionary Timetable  THE BIG BANG! (10-20 billion years ago)  Earth – 4.5 billion years ago  Primates – <65 million years ago  Mesozoic era “ age of reptiles  Cenozoic era “ age of man: The First Mammals  By 190 million years ago (mya) true mammals appear in the fossil record ◦ In geological terms, the end of the Triassic period/beginning of the Jurassic  Known largely from fossilized teeth and jaw parts ◦ Where we start to see major changes from reptiles to mammals ◦ Teeth and bone most likely to fossilize  Mammals flourish by 65 mya ◦ adaptive radiation  New and available ecological niches: ◦ extinction of dinosaurs ◦ mild climate favouring flowering plants  Separation of the continents ◦ Limits the ability for gene flow K-T Extinction (Cretaceous–Tertiary extinction)  65 mya – massive extinction of 75-85% of living species  Theories include: ◦ Meteorite impact ◦ Volcanic eruption ◦ Change in global conditions ◦ Competition with mammals ◦ Probably more complex than just one cause Cenozoic Era – TheAge of Mammals (Begins ~ 65 mya) • The Rise of Primates o Pliocene – hominid origins o Miocene – fossil hominoids (great apes) o Oligocene – fossil anthropoids (monkeys and apes) o Eocene – 1 appearance of ‘true’primates o Paleocene – primate-like mammals Key Concepts from the Text: Chapter 5 – Macroevolution • Homologies o Similarities between organisms based on descent from a common ancestor • Analogies o Similarities between organisms based strictly on common function, with no assumed common evolutionary descent • Homoplasy o Homo meaning same, plasy meaning growth o The separate evolutionary development of similar characteristics in different groups of organisms • Evolutionary Systematics o Atraditional approach to classification in which presumed ancestors and descendants are traced in time by analysis of homologous characters • Cladistics o An approach to classification that attempts to make rigorous evolutionary interpretations based solely on analysis of certain types of homologous characters • Ancestral vs. Derived o Ancestral: Referring to characters inherited by a group of organisms from a
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