http://www.bayshorewatershed.org/bw/Current%20Projects/%2A%20Horseshoe%20Crab%20Monitoring/Oldest%20Horseshoe%20Crab%20Fossils%20Found%20in%20Canada.html A new fossil species of horseshoe crab shows that the primitive marine creatures have existed for at least a hundred million years longer than previously believed, researchers say.