This is the skull of the most complete Tyrannosaurus rex ever found. The Black Hills Institute of Geological Research in Hill City, South Dakota excavated it. This picture was taken on Nov. 10, 2003 at the Smithsonian National Museum of Natural History.<br />
Fossil Crinoids (Uintacrinus socialis), Smithsonian National Museum of Natural History, Washington, D.C. Because many crinoids resemble flowers, with their cluster of waving arms atop a long stem, they are sometimes called sea lilies. But crinoids are not plants. Like their relatives—starfishes, sea urchins, sea cucumbers, and brittle stars—crinoids are echinoderms, animals with rough, spiny surfaces and a special kind of radial symmetry based on five or multiples of five.