bild 3 lecture 15

bild 3 lecture 15 - The Evolution of Animals With Backbones...

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The Evolution of Animals With Backbones The evolutionary history of the subphylum Vertebrata of the phylum Chordata is shown below. Chordates are animals with a dorsal nerve cord that runs the length of the body. This delicate nerve cord is protected by a rod of cartilage, called a notochord, that also acts to stiffen the body. In vertebrates the notochord is replaced during development by a cartilaginous or bony backbone that surrounds the nerve cord in the adult animal and protects it more effectively. Pelycosaurs and other "stem" rep- tiles Cynodont ("dog-toothed") therapsids Mammals Dicynodont therapsids ("two-toothed dogs") Ornithischian dinosaurs ("bird-like pelvis") Saurischian dinosaurs ("lizard-like pelvis") Bird-like dinosaurs Birds Dimetrodon grandis Turtles Crocodilians Lizards Snakes Jawed cartilaginous fish Osteichthyes (bony fish) Lungfishes Coelacanths Amphibians Tetrapods Emer- gence onto land Lobe-finned fish Jawless cartilaginous fish (e.g. lampreys) 1 2 3 4 5 Millions of years ago 6 Evolution of jaws We saw earlier how the birds evolved from a dinosaur lineage. Recently, short peptides of the protein collagen, the most plentiful protein in the body, have been analyzed from a 68 million year old Tyrannosaurus rex dinosaur bone. The sequences most closely matched those of chicken.
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Recently, a spate of exciting fossil evidence has helped to fill in some other parts of this tree. First, a “missing link” between fish and the earliest amphibians has been found in northern Canada, near the North Pole. This fossil, Tiktaalik, was named after an Inuit word for “large shallow-water fish.” It lived 375 million years ago, during the early Devonian. The animal, named Tiktaalik rosaea, had a neck, wristbones (but no paws, only fins), and many fish-like characters including scales and gills. Second, recent evidence from fossils from northern China shows that mammals evolved a variety of life styles earlier than we previously thought.
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An early Cretaceous mammal from the Liaoning beds of northern China was found with teeth and bones of a small dinosaur in its stomach. Below is how it may have looked!
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This fossil from the middle Jurassic of the same region, some 30 million years earlier, has preserved traces of fur. The animal was clearly aquatic, rather like a modern otter but with a beaver-like tail. The Genetic Basis of Macroevolutionary Change What were the genetic changes underlying these and other major diversifications that we can trace in the fossil and molecular records? We are beginning to discover some of them. An active debate continues over whether some of these changes have resulted from the fixation in populations of
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bild 3 lecture 15 - The Evolution of Animals With Backbones...

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