A little while back, I went on a tear about the phrase “living fossil.” We should scuttle the baggage-ridden aphorism – extant crocodiles, coelacanths, and tuataras are not “unchanged” remnants of an earlier era, but the last branches of amazing animal groups that flourished during Deep Time. I almost wish that I had waited another few weeks before tapping out my rant. That’s because of a new paper by Yale University paleontologist Derek Briggs and colleagues, which puts another misunderstood icon of stasis in context.

I have an abiding love for horseshoe crabs. The unusual arthropods are among evolution’s greatest survivors, but the species that crawl along the ocean bottom today are not exactly like their fossil relatives. This really