Fossil Mammal Reveals Clues About Mammalian Hearing

Photo © Mark A. Klingler / Carnegie Museum of Natural History.

A team of paleontologists have discovered a fossil of a 123-million-year-old mammal that lived in what is now the Lianoning Province of northeastern China. The mammal, Maotherium asiaticus, was so well preserved that it has provided scientists with new insights into the evolution of the mammalian middle ear.

"What is most surprising, and thus scientifically interesting, is this animal's ear. Mammals have highly sensitive hearing, far better than the hearing capacity of all other vertebrates, and hearing is fundamental to the mammalian way of life. The mammalian ear evolution is important for understanding the origins of key mammalian adaptations." ~ Dr. Zhe-Xi Luo, from Carnegie Museum of Natural History.

Mammals possess more acute hearing than other vertebrates, an adaptation that enabled early mammals to better evade predators in the dinosaur-dominated environment in which they first evolved. Mammalian hearing depends on three bones, the hammer (malleus), the anvil (incus), and the stirrup (stapes) as well as an eardrum (tympanic membrane). These structures were once part of the jaw bone in mammalian ancestors. In present day mammals, the bones are separate from the jaw. But in Maotherium asiaticus, there is still a connection between the middle ear bones and the jaw.