Crinoid

1. Glyptocrinus decadactylus
2. Ectenocrinus simplex

• Ordovician
•
• Madison, Indiana, USA or Cincinnati, Ohio, USA

Size: 9 cm crown for the Glyptocrinus, 5 cm crowns for the Ectenocrinus

1. Featured here is a Glyptocrinus decadactylus, a classic and fairly common Ordovician crinoid. It is a monobathrid camerate with prominent median ray ridges leading into 20 unbranched, uniserial pinnulate arms, and most distinctively, beautiful stellate ornamentation throughout the calyx plates, which makes the species a favorite among collectors. You can see the crinoids are lying on top of two more rather crushed Glyptocrinus and a bundle of stems. This may have been a gregarious species, as often plates are found with numerous individuals densely stacked right next to each other.

2. A classic Ordovician crinoid, Ectenocrinus simplex is a very common species that is extremely widespread throughout the continent of North America, including Quebec and Ontario of Canada, as well as New York, Indiana, Ohio, Kentucky, Iowa, Minnesota and Pennsylvania of the US. This is a disparid, which is rather unusual considering that disparids are often the rarer and more exotic members of a crinoid fauna. E. simplex has a slender crown that bears two pinnulated arms per ray with big, chunky square brachials; not quite as simplified nor specialized as some of its bizzare disparid relatives. Something about this body plan must have made it very successful to be so common and widespread.