Yanoconodon allini, artwork. This prehistoric mammal, here drinking from a stream in a forest, lived 125 million years ago during the Mesozoic Era. It was unknown until a fossil was discovered in Hebei Province in China, with the results being published in 2007. The fossil was well-preserved, and the structure of the bones of its middle ear provided important evidence on the early evolution of mammals. The new mammal also has lumbar ribs, a rare feature among modern mammals.