Nocturnal bottleneck
The nocturnal bottleneck hypothesis is an evolutionary biology hypothesis to explain the origin of several mammalian traits. In 1942, Gordon Lynn Walls described this concept which states that placental mammals were mainly or even exclusively nocturnal through most of their evolutionary history, from their origin 225 million years ago during the Late Triassic to after the Cretaceous–Paleogene extinction event, 66 million years ago.