Fossil shows how early mammals could swallow like their modern descendants

The 165-million-year-old fossil of a tiny, shrew-like animal shows the earliest example of modern hyoid bones-the ones that provide the ability to swallow food-in mammal evolution. The hyoid bones of Microdocodon gracilis -as well as all modern mammals, including humans-link the back of the mouth, or pharynx, to the openings of the esophagus and the larynx. They are arranged in a "U" shape, similar to the saddle seat of children's swing, suspended by jointed segments from the skull. It helps us transport and swallow chewed food and liquid-a crucial function on which our livelihood depends. Mammals are far more sophisticated than other living vertebrates in chewing up food and swallowing it one small lump at a time, instead of gulping down huge bites or whole prey like an alligator. "Mammals have become so diverse today through the evolution of diverse ways to chew their food, whether it is insects, worms, meat or plants. But no matter how differently mammals can chew, they all have to swallow in the same way," said Zhe-Xi Luo , a professor of organismal biology and anatomy at the University of Chicago and the senior author of a new study of the fossil, published this week in Science.