During the Mesozoic, we see the evolution of dinosaurs and their direct descendants; birds. However, dinosaurs were not alone during this era: mammals and crocodiles also appear (and diversify enormously), an overview of which is presented, as well as various types of animal and plant parasites. The chapter ends with the appearance of flowering plants and the phenomenon of pollination of these by biological vectors, especially bees. The social customs of these insects allow us to present the four recognized types of animal societies: colonial invertebrates, social insects, bird and mammalian societies, and human societies.