One day in a place that would someday be known as Montana , a juvenile Tenontosaurus was attacked and killed by a pack of raptors. More than 100 million years later, Sarah Werning learned something personal about the doomed animal: It was pregnant.

"It was totally unexpected,” Werning said.

Werning made the discovery in summer 2005 while she was working on her master's thesis at the University of Oklahoma . ...