The fossil record of phoronids is poor. There are borings dating back to the Devonian which have been attributed to phoronids. "Iotuba chengjiangensis", a form known from only three specimens in the Lower Cambrian, has been interpreted as a phoronid because it appears to have had a U-shaped gut and was tentaculated. Phoronids may be related to the common but mysterious tubular fossils known as hederellids.