SOFT-TISSUE PRESERVATION IN PROTASTERID OPHIUROIDS (ECHINODERMATA) FROM THE KOPE FORMATION (CINCINNATIAN, UPPER ORDOVICIAN) OF NORTH-WESTERN KENTUCKY AND THE HUNSRUECK SLATE (EMSIAN, LOWER DEVONIAN) OF GERMANY

Reports of pyritized, non-mineralized tissue preservation from the fossil record are very rare. We report pyritized tube feet in the holotype of the protasterid ophiuroid Protasterina fimbriata Ulrich from the Economy Member of the Kope Formation of the Cincinnatian of Kentucky. The incomplete specimen is nearly free of matrix and preservation is in three-dimensions. Ulrich (1878) observed structures filling and partially extending from the podial basins that he interpreted to be plates of uncertain nature. These structures are currently known only from some podial basins of the holotype and they are lacking from other specimens of the species. We re-interpret these structures as tube feet.

We recently reported discovery by another researcher of pyritized tube feet in the protasterid ophiuroid Bundenbachia beneckei from the Hunsrueck Slate. The discovery was made possible by development of new approaches to airbrasive preparation employing pure iron powder at low pressure. Since then we have discovered three of 17 additional specimens of B. beneckei with pyritized tube feet. Robust podial basins and tube feet in Bundenbachia suggest more discoveries will be made for this genus but occurrences might not be found in taxa with smaller, more delicate basins. Differences in podial robustness might reflect behavioral and niche differentiation. Extant asteroids, which have a broad range of tube foot morphology, provide possible analogies.

The discovery of non-mineralized tissue preservation in the fossil record is problematic. In the Hunsrueck Slate, pyritized soft-tissue has been reported from over 20 groups but all such occurrences have been vigorously debated, especially structures that are visible only on radiographs. Otto (1994, 2000) has been a particularly vigorous critic of soft-tissue preservation in the Hunsrueck. In contrast, discovery of pyritized tube feet in two disparate settings strongly supports hypotheses of volatile soft-tissue preservation by early diagenetic pyrite.