Site-selectivity of symbiotic (parasitic?) pits in crinoid column material from the middle Silurian (Wenlock: Sheinwoodian) of western Estonia

Abstract

Crinoid specimens containing symbiotic (potentially parasitic) pits are relatively rare in Silurian strata of Estonia. The first specimen of middle Silurian-age (Wenlock: Sheinwoodian) crinoid material containing such pits—a pluricolumnal of uncertain affinity—was recently reported from the Jaagarahu Formation of Saaremaa Island. The presence and morphology of pits were previously described, but a noteworthy paleoecological phenomenon that was not initially documented involves the site-specificity of pit occurrence along the pluricolumnal. All 21 of the pits distributed around the lateral circumference of the specimen are located on plate sutures, demonstrating a degree of site-selectivity that contrasts strongly with the more random distribution of pits observed in most Silurian crinoid assemblages. The underlying paleoecological driver of this site-selectivity remains enigmatic, particularly considering some reports that suggest a preference for the latera rather than the sutures of Paleozoic crinoid columns.

Keywords:

• Echinodermata
• Tremichnus
• Oichnus
• embedment structures
• Baltica

Acknowledgments

Previous versions of this contribution were improved by the reviews provided by Carlton E. Brett (University of Cincinnati) and an anonymous reviewer.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Research on the Silurian crinoid fauna of Estonia was funded by a Palaeontological Association Research Grant, a Paleontological Society Sepkoski Grant, and Estonian Research Council project IUT20-34 to OV. G. Baranov (Tallinn University of Technology) photographed the studied specimen.