The modern crinoid fauna is diverse, numbering approximately 600 species (Hess and Ausich 1999), all of which are assigned to the subclass Articulata Miller 1821 (Hess 2011). The Articulata is one of five crinoid subclasses and the only one of the post-Paleozoic (Simms 1999); the other four subclasses are thought not to have survived the Permo-Triassic extinction event. In part due to the sparse fossil record of crinoids during this critical interval, several aspects of crinoid evolutionary history have yet to be resolved. Among them are:
- The monophyly of post-Paleozoic crinoids (the Articulata) and
- The identity of the most recent common ancestor(s) of post-Paleozoic crinoids.
Exploring these questions will involve a phylogenetically focused study of fossil crinoids of the middle to late Paleozoic as well as the early Mesozoic.