Crinoid

Paramphicrinus oklahomaensis

• Pennsylvanian
• LaSalle Limestone, Bond Formation
• Pontiac, Illinois, USA

Size: 4.5 cm across the arms

Flexible crinoids were unusual during the Pennsylvanian, and Paramphicrinus oklahomaensis is the rarer of the two found in the Pontiac fauna. At a glance this crinoid seems similar to the commonly-seen Mississippian flexibles such as Taxocrinus and Onychocrinus, but some notable differences are that the rays and arms are packed very closely together and tightly fused by interradial plates, and that the arms branch many more times towards the tips (reaching between 80-100 arms in total) and are more strongly incurved. These traits in addition to others give the crown an overall very stout, compact, globe-like form.