Horseshoe crabs are survivors by anyone’s measure; they have carried on their lives virtually unchanged, according to the standard evolutionary timeline, for 450 million years.  This not only points to incredible stasis against alleged forces of evolution; it also means they have survived at least three global extinctions that evolutionary biologists and geologists say wiped out most other species.  Not only that, the world has changed drastically since they allegedly evolved from who-knows-what arthropod ancestors – perhaps trilobites, that appeared in the Cambrian Explosion without ancestors.  But the numerous, successful trilobites did not survive the global extinctions.  Given these contradictory facts, how can the horseshoe crab possibly be an exhibit for evolution?  A recent article shows how.

Horseshoe crabs are not crabs; they are arthropods, similar in some ways to scorpions.  The UK Natural History Museum gave facts and fancies about these amazing, complex animals on the verge of a BBC News special TV program about them:

The Great Dying wiped out most of the Earth’s species.  Some scientists have estimated 96% of marine species, 70% of terrestrial vertebrates and 57% of insect families became extinct. But the strange-looking horseshoe crab, with its armoured shell and long rigid pointed tail, lived on… These animals have survived 3 of Earth’s extinctions that wiped out most other species.

If humans learned their secrets, maybe they could do better on the Survivor reality shows.  What are their secrets?  Fossil expert Richard Fortey lists some possibilities in the article: (1) being able to eat almost anything, (2) getting by with less oxygen, (3) salt tolerance, and (4) having a kind of blood that shields against bacteria.  If those traits are so evolutionarily successful in one of the earliest animals, it’s a wonder every other animal didn’t mimic them.  Presumably the trilobites had these traits, but they went extinct anyway….

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