Presentation on theme: "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."— Presentation transcript:
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
1. Mammal-like reptiles - mammals Pelycosaurs Therapsids Permian MLR Triassic MLR Cynodonts Mammals Monotremes Marsupials Mammals Gradual acquisition of mammalian characteristics By end Triassic
2. What characters make a mammal? Erect gait Furry Secondary palate Warm blooded Simple jaw, complex jaw muscles Specialised teeth - usually grow once Ears with ear bones Diaphragm Suckle young, but may still lay eggs
2b. What skull characters make a mammal? Reptilian jaw Mammalian jaw Quadrate Jaw hinge Articular Dentary Simple bite Simple teeth Squamosal Secondary palate Complicated bite Specialised teeth Masseter muscle Dentary Jaw hinge Squamosal Articular and quadrate now ear bones
3. Mammal-like reptiles Thrinaxodon Some tooth specialisation Secondary palate Chewing muscle Complex jaw, no ear bones Rigid spine ?Fur Endotherm ?Diaphragm Sprawling gait Small size = small eggs, small hatchlings, much care,? suckling?
4. Mammals and dinosaurs Monotremes probably evolved near Jurassic/ Cretaceous boundary. Precise ancestry uncertain Marsupials Cretaceous origin, evolved on Gondwana Mammals Cretaceous origin. Evolved on Laurentia Multituberculates successful Mesozoic clade, known principally from teeth Morganucodon Lower Jurassic tiny, agile carnivore with complicated teeth Limited Mesozoic radiation, all animals under 15kg. Mainly small scavengers and carnivores.
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
6. Mammals on a cooling Earth Palaeogene Earth Neogene Earth Warm,wet,low ice, abundant forests Cool, dry, large icecaps, evolution of grass, formation of widespread savanna Himalayas rise Americas collide Many isolated continents promote intense speciation Continental collision and climate change precipitate major extinction modern mammals survive and radiate
6b. Dinosaurs arrive Archosaurs 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 Birds Early Jurassic Ischium and pubis Ischium Pubis Illium