Picture of an extremely old fossil of red alga.  This fossil is on display at the Smithsonian Museum of Natural History and is called Gryp...

Tylocidaris clavigera (Mantell, 1822) cast of a sea urchin fossil found in England.  The creature existed in the Cretaceous Period.  Cast...

Stereocidaris hemigranosus sea urchin fossil on display at the Smithsonian National Museum of Natural History in Washington, DC.  The fos...