His question was to why "small dinosaurs" did not have the same chances as mammals. Large dinosaurs(there were no large mammals, but if there were it would app

His question was to why "small dinosaurs" did not have the same chances as mammals. Large dinosaurs(there were no large mammals, but if there were it would apply the same to them) had different issues then the rest, mainly two different things, food and oxygen. The first reason food, is the main reason. These large animals required huge amounts of food to survive. As the ecosystems collapsed the available food supplies dropped to almost nothing. The second reason and the same that animals grew to be so large during this time period is predominantly because the oxygen levels were much much higher then they are now. As the ecosystem collapsed so did the oxygen levels. This is why we do not have larger animals now.