Sea cucumbers are hard to find in the fossil record because their skeletons are made up of many, miscroscopic pieces (ossicles) that are easily overlooked. Only a couple dozen full body fossils have been found, so most of what we know about the evolutionary history of sea cucumbers is from ossicles. Ossicles do not give you a clear picture of sea cucumber abundance or diversity because they can differ within one individual, or depending on an individual’s age. The oldest known fossil sea cucumber ossicle is from the late Silurian (about 420 million year ago). Paleontologists believe that sea cucumbers may have been around earlier than that, and continue to analyze what organisms they evolved from. Possible ancestors may are little-known “calledophiocistioids” or ancient sea urchins. Because sea cucumbers look like giant larvae, it has even been proposed that they evolved as a group of adults keeping the characteristics of larvae (paedomorphism).