When it comes to fossils, preserving the hard stuff is easy. It's the soft parts, like muscles and skin, that tend
to elude scientists. So it's something of a shock that the oldest shrimp on record—from an estimated 360 million years ago—still has its muscles
nicely sculpted in stone (above). Researchers found the 70-millimeter crustacean in the dark shale of an Oklahoma quarry. Much of its body was
shattered, but they could still make out the fine lines of its muscle bands. Low oxygen and low pH levels may have helped preserve the soft tissue, the
team reports in a paper published this week in The Journal of Crustacean Biology. In an ocean without oxygen, like the one this shrimp died in,
minerals like apatite can precipitate out and replace the soft tissue, but only if the creature becomes buried in a matter of days.
See more ScienceShots.