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The Vertebrate Genealogy Chapter 30 What is a chordate? There are 4 anatomical structures that appear during some point during the animal’s lifetime: 1. Notochord – long flexible tube between the gut and the nerve cord - becomes gelatinous material between vertebrae in humans 2. Dorsal, hollow nerve cord – becomes CNS 3. Pharyngeal slits 4. Muscular postanal tail – most chordates have a tail that extends beyond the anus What is a chordate? Survey of Vertebrate Classes Fishes: Agnatha, Chondrichthyes, Osteichthyes Tetrapods: Amphibia, Reptilia, Aves, Mammalia Amniotes: Reptilia, Aves, Mammalia Have a shelled water-retaining egg Class Agnatha Sample organisms: Hagfishes, lampreys Jawless vertebrates Feed by sucking blood after clamping onto prey or by scavenging Do not have paired appendages Class Chondrichthyes Sample organisms: sharks and rays Cartilaginous fishes – have relatively flexible skeletons made of cartilage rather than bone Most sharks are carnivorous and have acute senses Class Osteichthyes Bony fishes Have hard skeletons (due to ossification) Sample organisms: perch, trout Breathe by drawing water over 4-5 pairs of gills covered by operculum (protective flap) Most bony fishes are oviparous Females lays large numbers of eggs, fertilization occurs externally Class Osteichthyes Class Amphibia The first vertebrates (tetrapods) on land Amphibians must deposit their shell-less eggs in water Sample organisms: frogs & salamanders Amphibian = “two lives” Tadpole – larval stage Metamorphosis occurs Frog – legs develop Salamanders – have tails Frogs – do not have tails The Amniotic Egg The amniotic egg is a reproductive adaptation that allowed terrestrial vertebrates to complete their life cycles on land The shell prevents the egg from drying out 4 layers of protection: Amnion – prevents dehydration, cushions shocks Yolk Sac – stockpile of nutrients Allantois – disposal sac for certain metabolic wastes Chorion – gas exchange Class Reptilia Sample organisms: lizards, snakes, turtles, crocodiles Reptiles have scales made of keratin that cover their skin Obtain oxygen with their lungs Fertilization occurs internally Most reptiles lay amniotic eggs on land Ectotherms – body temperature fluctuates with the environment Class Aves Birds are tetrapods with feathers Their forelimbs are modified as wings Sample organisms: owl, sparrow, penguin, eagles Lay amniotic eggs Endothermic – regulate their own body temps. Anatomy adapted for flight Form & function Class Mammalia Mammals have hair Endothermic Mammary glands that produce milk Most mammals are born, not hatched Three major groups: Monotremes – lay eggs Marsupials – complete development in a maternal pouch platypuses, echidnas Kangaroos, koalas, opossums Placental mammals – complete development within the uterus, joined to the mother by the placenta Sheep, bats, elephants, humans Paleoanthropology Paleoanthropology is the study of human origins and evolution Correcting misconceptions: “Let’s first dispose of the myth that our ancestors were chimpanzees or any other modern apes. Chimpanzees and humans represent two divergent branches of the anthropoid tree that evolved from a common, less-specialized ancestor.” Paleoanthropology 1974 – Ethiopia Homo habilis “Lucy” is an Australopithecus skeleton 3.18 million years old 2.5 million years ago Enlargement of the human brain Homo erectus First hominid to migrate out of Africa into Asia and Europe Taller than H. habilis and a larger brain capacity Paleoanthropology 2 models of how Homo sapiens evolved To think about… “Of the many crises in the history of life, the impact of one species, Homo sapiens, is the latest and potentially the most devastating.” - Neil Campbell, 4th ed.