 Most of the Cambrian stratigraphy is based on the use of trilobite marker fossils.Trilobites are the state fossils of Ohio ("Isotelus"), Wisconsin ("Calymene celebra") and Pennsylvania ("Phacops rana").The 10 trilobite orders are Agnostida, Redlichiida, Corynexochida, Lichida, Odontopleurida, Phacopida, Proetida, Asaphida, Harpetida and Ptychopariida.