Trilobite fossils date from the Cambrian era, over 500 million years ago. Specimens of this age can be found in Britain Canada, Morocco, Spain and the United States Russia. Trilobites filled the oceans for millions of years but became extinct before the age of dinosaurs began 250 million years ago. then came the ammonite fossil that plagued the seas. british ammonite fossils are one of the best ammonites  in the world