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Unformatted text preview: Lecture 17 Mesozoic Life A. Classifying amniotes-  Skull conditions- evolution and classification of tetrapods  Tetrapods are grouped according to the position and number of temporal openings in the skull B. Early Synapsids-  Early synapsides from the Permian- defined by synapsid skull condition sometimes mislabeled mammal like reptiles  The “sail-backs” are loosely known as the pelycosaurs that includes both herbivores and carnivores C. Dimetrodon- A pelycosaur  Synapsid skull condition, called “sail-lizards” but should be “sail- synapsids” (lizards are diapsids)  Dimetrodon is carnivorous to other pelycosaurs, use of sail, heat collector radiator- likely both D. Therapsids-  Advanced rapidly in the Late Permian, includes cynodonts and dicynodonts  Therapsids had more powerful jaws and had better locomotion than pelycosaurs (the earlier synapsids)  Often called “mammal-like reptiles” (but they’re not reptiles) o Call them “reptile-like synapsids” instead E. Therapsids- Dicynodonts  Evolved in the Late Permian, dominant herbivores during that time  The jaws have some sort of horny beak (like turtles), and a horny feeding structure replaced throughout their life  They were very successful in their time- the first truly abundant nearly worldwide herbivores  Many small, but they ranged from rat to cow-sized, later evolved effective cutting and grinding teeth F. Therapsids: Cynodonts-  Appeared near the end of Permian, two lineage survived and flourished in the Triassic  Generally small to medium sized, innovation in food processing, chewing o Led to evolution of jaw, tooth, and skull features now skull feature now seen in mammals  Predators, fed on dicynodonts, had fur, possibly warm- endothermic...
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This document was uploaded on 04/25/2008.
- Winter '08