it could be aloght of things heres the most likely awnser * a giant meteor the size of everest slams into earth at the around the big peninsula in mexico in the gulf of mexico about 65 million yrs. ago makeing many dinosaurs ,pterasaurs ,plants and some giant crocs die out the impact is estamated to be more than 100 atomic bombs going of at the same time that would send huge shock waves all over the world.this made huge black dust clouds covering half of earth witch made plants die makeing herbivores (plant eaters) die then carnivores (meat eaters) would have to kill other carnivores witch lead to extinction if this didn't wipe out some ther could be disease killed some mammals that were small at the time ate there eggs helpped in this crises.