To get a left-leaning impression in the sand, the shell must've been asymmetrical, like a modern-day conch shell. But twisted shell fossils don't appear until the early Ordovician, tens of millions of years after the arthropod traipsed through the sand. Hagadorn admits the notion of innovative hermit arthropods crawling in the open 500 million years ago is speculative. And all he and Seilacher have to go on right now are a series of tracks -- no body fossils have been discovered. "I am confident the animal that made these tracks was an arthropod. I am not at all confident it was a hermit arthropod," Hagadorn said. "It's the best idea we've got, though. It's kind of like solving a crime without the murder weapon or DNA evidence." Related Links: Go to Discovery Earth for slide shows, quizzes, interviews and more. |
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