Horseshoe Crabs Have Stayed Basically the Same for 450 Million Years

Horseshoe crabs are often called “living fossils” because, although they’ve continued to evolve like all living species, their overall body plan has remained remarkably similar for about 450 million years. Their ancient ancestors lived long before dinosaurs, and these resilient marine animals have survived mass extinctions, ice ages, shifting coastlines, and dramatic changes to Earth’s environments.

Much of their long-term success comes from a robust body design that has stood the test of time. Their hard shells, multiple eyes, and long, pointed tails have remained highly effective adaptations for hundreds of millions of years. Today, horseshoe crabs inhabit shallow coastal waters, where they play an important role in marine ecosystems, proving that evolution often preserves traits that continue to provide a survival advantage.