remains wrote:
dinosaurs died off (/evolved into birds) bcs the habitat changed drastically and nothing that large could survive at that time -> extinction event
n after that mammals evolved to take up all the available niches
just like a group of reptiles evolved into dinosaurs bcs of an extinction event that killed vast majority of large life forms on land including most pre-mammals
so basically. habitat and food and whoever can evolve quickest to fill the space available