Editing Crinoid (section)

=== Origins ===
[[File:Agaricocrinus americanus Carboniferous Indiana.jpg|thumb|''[[Agaricocrinus americanus]]'', a fossil crinoid from the [[Carboniferous]] of Indiana]]
[[File:JurassicCrinoidsIsrael.JPG|thumb|Middle [[Jurassic]] ([[Callovian]]) ''Apiocrinites'' crinoid pluricolumnals from the [[Matmor Formation]] in southern Israel]]

If one ignores the enigmatic ''[[Echmatocrinus]]'' of the [[Burgess Shale]], the earliest known unequivocal crinoid groups date back to the [[Ordovician]], 480 million years ago. There are two competing hypotheses pertaining to the origin of the group: the traditional viewpoint holds that crinoids evolved from within the [[blastozoa]]ns (the [[Eocrinoidea|eocrinoids]] and their derived descendants, the [[blastoid]]s and the [[Cystoidea|cystoids]]), whereas the most popular alternative suggests that the crinoids split early from among the [[Edrioasteroidea|edrioasteroids]].<ref name="Guensburg2010">{{cite journal |doi=10.1111/j.1502-3931.2010.00220.x |title=Pelmatozoan arms from the mid-Cambrian of Australia: Bridging the gap between brachioles and brachials? Comment: There is no bridge |journal=Lethaia |year=2010 |last1=Guensburg |first1=Thomas E. |last2=Mooi |first2=Rich |last3=Sprinkle |first3=James |last4=David |first4=Bruno |last5=Lefebvre |first5=Bertrand |volume=43 |issue=3 |pages=432–440|bibcode=2010Letha..43..432G }}</ref> The debate is difficult to settle, in part because all three candidate ancestors share many characteristics, including radial symmetry, calcareous plates, and stalked or direct attachment to the substrate.<ref name="Guensburg2010"/>