Artwork by Todd Marshall, courtesy of Project Exploration In a painted scene set 90 million years ago—at the edge of a lake in what is today the Gobi Desert of Inner Mongolia—a herd of young Sinornithomimus dinosaurs suddenly finds itself trapped in mud. Chinese and American paleontologists, including Paul Sereno, Professor in Organismal Biology & Anatomy, excavated the site in 2001. Sereno, who also is a National Geographic Explorer-in-Residence, and his Chinese associates discussed their discovery during a Monday, March 16 news conference in Hohut, Inner Mongolia. The sudden death of the herd in a mud trap provides a rare snapshot of their social behavior.