Graptolithina is a subclass of the class Pterobranchia, the members of which are known as graptolites. These organisms are colonial animals known chiefly as fossils from the Middle Cambrian (Miaolingian, Wuliuan) through the Lower Carboniferous (Mississippian). A possible early graptolite, "Chaunograptus", is known from the Middle Cambrian. One analysis suggests that the pterobranch "Rhabdopleura" represents extant graptolites. Studies on the tubarium of fossil and living graptolites showed similarities in the basic fusellar construction and it is considered that the group most probably evolved from a "Rhabdopleura"-like ancestor.