Lecture 17 - Lecture 17 Mesozoic Life A Classifying...

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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 
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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 
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