Description: [caption id="" align="aligncenter" width="408" caption="The skeleton of a Hyracotherium, a tiny horse that heralded one of the major evolutionary trends of the age of mammals - the move to grazing - from the National Museum of Natural History's new exhibit "Mammals in the Limelight," opening May 30, 1985, In the background is Robert Emry, Curator of fossil mammals in the