These included the first fully aquatic mammals (whales) and flying mammals (bats), as well as rodents and primates. This sudden expansion of species diversity into new ways of life is known as ...

as these distinguishing rocks were first studied in Devon, England. The Devonian, part of the Paleozoic era, is otherwise known as the Age of Fishes, as it spawned a remarkable variety of fish.

This suggests the gene network that makes the elastic cartilage in the fish gills became active in reptiles’ ear canal first and then in mammals’ outer ear. “So what we imagine is ...