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The origin and rise of mammals

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1 The origin and rise of mammals
1. Mammal-like reptiles - mammals 2. What is a mammal? 3. Mammal-like reptiles 4. Mammals and dinosaurs 5. Palaeogene radiation of mammals 6. Mammals on a cooling Earth

2 1. Mammal-like reptiles - mammals
Marsupials Mammals Monotremes Triassic MLR Mammals By end Triassic Cynodonts Permian MLR Therapsids Gradual acquisition of mammalian characteristics Pelycosaurs

3 2. What characters make a mammal?
Suckle young, but may still lay eggs Furry Ears with ear bones Secondary palate Specialised teeth - usually grow once Simple jaw, complex jaw muscles Warm blooded Diaphragm Erect gait

4 2b. What skull characters make a mammal?
Reptilian jaw Simple teeth Quadrate Jaw hinge Squamosal Articular Simple bite Dentary Mammalian jaw Articular and quadrate now ear bones Secondary palate Squamosal Jaw hinge Complicated bite Dentary Specialised teeth Masseter muscle

5 3. Mammal-like reptiles Thrinaxodon Some tooth specialisation
Secondary palate Rigid spine Complex jaw, no ear bones ?Fur Chewing muscle Endotherm ?Diaphragm Sprawling gait Small size = small eggs, small hatchlings, much care,? suckling?

6 4. Mammals and dinosaurs Limited Mesozoic radiation, all animals under 15kg. Mainly small scavengers and carnivores. Mammals Cretaceous origin. Evolved on Laurentia Marsupials Cretaceous origin, evolved on Gondwana Monotremes probably evolved near Jurassic/ Cretaceous boundary. Precise ancestry uncertain Multituberculates successful Mesozoic clade, known principally from teeth Morganucodon Lower Jurassic tiny, agile carnivore with complicated teeth

7 5. Palaeogene radiation of mammals
Large flightless birds radiated to become top terrestrial predators Large crocodiles radiated to become top marine predators Mammals radiated into a large range of other niches. 90% of mammalian groups appeared within 10 Ma of dinosaur extinction. Initially herbivores, omnivores, insectivores, scavengers. Gradually replaced birds and reptiles

8 6. Mammals on a cooling Earth
Palaeogene Earth Warm,wet,low ice, abundant forests Many isolated continents promote intense speciation Neogene Earth Cool, dry, large icecaps, evolution of grass, formation of widespread savanna Himalayas rise Americas collide Continental collision and climate change precipitate major extinction modern mammals survive and radiate

9 6b. Dinosaurs arrive Illium Birds Early Jurassic Ischium and pubis
Sauropods lizard-hipped. Vegetarians Evolved extremely large size, often in excess of 20 m in length and 50 tonness in weight. Theropods Late Triassic. All theropods were predators, including Tryannosaurus rex. Ornithischians bird hipped dinosaurs All herbivores, including armoured forms Iguanadonts and duck-billed dinosaurs. Highly modified teeth and jaws Illium Pubis Ischium Archosaurs

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