Evolutionary History
Horseshoe crabs are commonly known by biologists around the world as a living fossil because they have remained practically unchanged in terms of shape and size for millions of years. Although their physiology has changed over the years, their typical three piece exoskeleton, consisting of a prosoma, opisthosoma, and telson, has remained since the mid-Paleozoic era. Fossils of horseshoe crabs that have been dated to over 400 million years ago look almost identical to those species that are still alive today. The long existence of this body plan suggests its success. It is estimated that the American species of horseshoe crab diverged from the three Indo-Pacific species approximately 135 million years ago.
Read more about this topic: Mangrove Horseshoe Crab
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