Crinoid

Uintacrinus socialis

• Cretaceous
• Mancos Shale
• Colorado, USA

Size: 11 cm crown

Here is a classic rarity from the western/midwestern United States and an unmistakably unique and bizarre form. Uintacrinus was an unusual post-paleozoic crinoid with no stem and a ball-like calyx with numerous plates. It was probably a free-floating crinoid that drifted through the ocean while trailing its ten long arms to feed, somewhat like a jellyfish. It also seems to have been a colonial animal that traveled in large groups, as its fossils are generally found as groupings of many individuals with countless entangled arms.

Addendum: More recent theories postulate that Uintacrinus lived a benthic rather than pelagic lifestyle, buried in soft sediment as colonies and gathering food with their extraordinary long arms.