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The horseshoe crab (Limulus polyphemus), is the oldest living fossil in Maryland. Horseshoe Crabs evolved much earlier than
humans or the Chesapeake Bay. Fossils of horseshoe crabs have been dated at 360 million years old. They evolved in the shallow
seas of the Paleozoic Era (540-248 million years ago) with other primitive arthropods called trilobites, a long extinct close relative
of the horseshoe crab.
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The age of the dinosaurs, Mezozoic Era, began about 200 million years ago. During this period, dinosaurs dominated the landscape
as most species of marine reptiles became extinct. Also, the first mammals appeared. At this time, the shallow seas around Europe
were considered the dispersal point for ancestors of our modern day horseshoe crab species. At the end of the Era, a major
extinction of the dinosaurs and about half of the planet’s marine invertebrates occurred. The Horseshoe Crab survived this time of
change.
 (trilobite)
or use the glossary located at the top of the page.
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| Updated July 22, 2005 |