What is the only mammal that is known to truly fly?

Bats are indeed the only mammals that possess the ability to engage in true powered flight. This is a distinctive feature that sets them apart from other mammals and flying animals. Unlike gliding animals such as flying squirrels and colugos, which can only glide through the air without flapping their limbs to generate lift, bats are capable of sustained flight through their highly adapted wings made from a thin membrane of skin stretched over elongated fingers. This adaptation allows bats to maneuver effectively and forage for food while in midair.

Additionally, while birds are often associated with flight, they are not mammals; therefore, they do not fit the definition of the question. Understanding this unique aspect of bats highlights the diversity of adaptations that allow different species to exploit various ecological niches, including the ability to fly.