Crinoid

Grenprisia billingsi

• Ordovician
• Bobcaygeon Formation
• Simcoe County, Ontario, Canada

Size: 9.5 cm crown including anal sac

Grenprisia is a very unusual Dendrocrinid crinoid genus with features as unconventional as its name. Foremost, it possesses small interradial plates between its primibrachials and hence slight incorporation of the brachials into the calyx, which by strict definitions would exclude the genus from the Dendrocrinids and even the Cladids. Frank Springer considered it to be an intermediate form hinting at the Cladid origin of Flexible crinoids, much like Cupulocrinus (Springer 1911). The genus also exhibits a massive anal sac with stellate ornamentation true to the Dendrocrinids, but with plates organized irregularly as opposed to longitudinally as in other Dendrocrinids. It also appears to be the first of the Dendrocrinids to show a tendency towards pinnulation in the fossil record (Springer 1911).

Grenprisia billingsi is further characterized by its striking arms, which have a serpentine or "squiggly" appearance and branch heterotomously to produce many secondary ramules. The plates of the anal sac transition rather abruptly from small stellate plates to "thicker, more irregularly shaped bulbous plates" (Wright et al. 2019) in a rounded, balloon-like termination. Together these features form a crinoid with an instantly recognizable appearance among cladids.

This particular specimen is one of the finest G. billingsi I have ever seen and possibly the most complete crown ever found, with near-complete arms and a complete anal sac.

As an aside, the history of G. billingsi's name is quite interesting. Frank Springer erected the taxon as Ottawacrinus billingsi, with the specific name honoring Walter R. Billings who erected the genus Ottawacrinus (Springer 1911). Some fifty years later, Raymond C. Moore excluded the crinoid from Ottawacrinus and erected the genus Grenprisia to accomodate it, using an anagram of "Springer" to in turn honor Frank Springer (Moore 1962). Hence Grenprisia billingsi came to be as a result of giants in crinoid paleontology honoring their predecessors throughout time.