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.