Lecture 21: Evolution of mammals Flashcards
Principle of natural selection
Individuals compete for space, food and other resources,
individuals produce more offsprings than can survive, individuals vary in their traits. Due to limited resources only some offspring will survive, nature chooses variation in traits which assure survival and passed them on
Did mammals have an advantage over Dinosaurs?
Smaller size
Retaining more options: such as flexibility to swim, climb, dig, run, jump
Larger species had to specialize harder to adapt to a changing environment
Mammal diversity
less diverse than: fish, reptiles, birds
Fossil record of mammals
Transition from reptiles to mammals is poorly preserved
Features such as: hair, fur mammary glands have poor fossil record
Origins of mammals
Origin in late triassic
earliest finds date 225-220Ma but these barely made it over the triassic extinction
Evolution of mammals
mammals remained in small for about 115 ma, radiation after mass extinction of reptiles, by late paleocene (58ma) most of major groups of mammals had evolved
1st stage in mammalian evolution
Triassic to jurassic egg layers comparison with platypus small, mouse sized nocturnal fossils are often teeth
2nd stage in Mammalian evolution
Jurassic-Cretaceous
5 orders of primitive mammals have evolved: Multituberculates, Symmetrodonts, pantotheres, Marsupials, placentals.
late cretaceous: larger mammal species: creodonts (flesheaters) Condylarths (planteaters- first ungulates [hoofed animals])
3rd stage in mammalian evolution
Early cenozoic after mass extinction, expansion of mammals into new niches left by dinosaurs
The rise of mammals was the ______, not the _______ of dinosaur extinction
Effect;cause
How do mammals differ from reptilian ancestors?
Locomotion from sprawling to semi erect
change of elbows and knees
hands and feet moved closer to body’s center of gravity
less need for large limb muscles
Feeding characteristics
Mammals: lower jaw is one bone adding strength, incisors for biting; canines for tearign; molars for grinding
Endothermic or ectotherms?
Mammals are endotherms high rate of metabolism high rates of activity requires high rate of food intake fur for insulation sweat glands for cooling
Why were they outcompeted by reptiles?
Endothermy seems advantageous in cool climates, but most of the meoszoic climates were warm
Food requirements
Mammals need 10-13 times as much food energy as reptiles or amphibians to maintain body mass, this amount of food may not have been available
