AN UNUSUAL ASSOCIATION OF PSEUDOLINGULA AND RAFINESQUINA FROM THE UPPER ORDOVICIAN OF OHIO

Late Ordovician members of Order Lingulida, for the most part, resemble modern lingulids in their infaunal habits and marginal habitats. Pseudolingula, a common Cincinnatian form, is often found preserved in burrows in life position, and as such, it could probably escape moderate sediment accumulations. An unusual association of thousands of specimens of the lingulate Pseudolingula and hundreds of the strophomenid Rafinesquina in the Upper Ordovician of the Cincinnati, Ohio region presents an interesting case. This association occurs on 4-square-meter exposure of a 10 cm shell bed in the Fairview Formation at Harsha Lake, Ohio. The bed is covered with Rafinesquina and shows evidence of winnowing, presumably the result of a tropical storm.

Pseudolingula are concentrated near the center of both pedicle and brachial Rafinesquina valves. Thin sectioning of 15 isolated Rafinesquina shows that the lingulates were embedded in the cements that formed just under the shells. All lingulates are articulated and filled with sparry cement, and all Rafinesquina are disarticulated. Lingulates are segregated to areas immediately beneath Rafinesquina shells. Short segments of what might be vertical burrows containing lingulates terminate below some shells.

The lack of either disarticulated lingulates or articulated Rafinesquina confirms that the lingulates were alive and Rafinesquina dead at the time of burial. The concentration of Pseudolingula just beneath Rafinesquina shells suggests a non-random association. These facts suggest two hypotheses. 1) Pseudolingula might have attached to and sheltered under dead Rafinesquina shells which were then reworked by storm currents, or 2) lingulates escaping burial might have been entrapped under the re-deposited strophomenids as they burrowed upward. The first hypothesis suggests an unusual life mode for Pseudolingula and for that reason alone seems unlikely, but cannot yet be refuted. The second hypothesis suggests an interesting case of failure to escape resulting in an unusual association. Currently work is underway to test these hypotheses by sectioning the whole bed thickness to confirm whether escape burrows exist and, if so, establish their extent and nature.