Despite their modern abundance, due to their small size and fragility, copepods are extremely rare in the fossil record. The oldest known fossils of copepods are from the late Carboniferous (Pennsylvanian) of Oman, around 303 million years old, which were found in a clast of bitumen from a glacial diamictite. The copepods present in the bitumen clast were likely residents of a subglacial lake which the bitumen had seeped upwards through while still liquid, before the clast subsequently solidified and was deposited by glaciers. Though most of the remains were undiagnostic, at least some likely belonged to the extant harpacticoid family Canthocamptidae, suggesting that copepods had already substantially diversified by this time. Possible microfossils of copepods are known from the Cambrian of North America. Transitions to parasitism have occurred within copepods independently at least 14 different times, with the oldest record of this being from damage to fossil echinoids done by cyclopoids from the Middle Jurassic of France, around 168 million years old.