The answer is external stimulus
Answer:
the maintenance of constant osmotic pressure in the fluids of an organism by the control of water and salt concentrations.
Explanation:
After the Cretaceous–Paleogene extinction event wiped out the non-avian dinosaurs (birds being the only surviving dinosaurs) and several mammalian groups, placental and marsupial mammals diversified into many new forms and ecological niches throughout the Paleogene and Neogene, by the end of which all modern orders had appeared.
