One common Oklahoman graptolite was "Climacograptus". It correlates well with the occurrence of widespread graptolite, conodont, and trilobite species. Most are carbonate rocks with 23 different known graptolite zones. Brachiopod, mollusk, trilobite, ostracod, bryozoan, graptolite and stromatoporoid fossils are especially common. Climacograptus was a Cambrian genus of graptolite. Thecal shape is also important in graptolite taxonomy. Shale with graptolite fossils in the northeast belong to the Early Ordovician. Pyritized graptolite fossils are also found. Chaunograptus is a genus of putative graptolite known from the Middle Cambrian Burgess Shale. This is due to the strata that the graptolite is within, being folded and compacted. In some places these graptolite fossils are common. It preserves mollusk, coral, brachiopod and graptolite fossils dating back to the Ordovician period. The lower boundary is defined as the first appearance of the graptolite species "Tetragraptus approximatus". A possible early graptolite, "Chaunograptus", is known from the Middle Cambrian. This particular genus contains large number of graptolite species and may not be monophyletic.