Abstract

Since population studies are most reliable when applied to census assemblages, edrioasteroid paleoecology can best be understood by examining catastrophically buried obrution communities. This paleoecologic study examines a carbonate hardground surface encrusted with four species of isorophid edrioasteroids: Curvitriordo stecki, Carneyella ulrichi, Carneyella pilea, and Streptaster vorticellatus. Analysis of edrioasteroid diameters, a proxy for age, shows a bimodal distribution for Curvitriordo stecki, suggesting a hiatus in recruitment or multiple spatfalls. Low juvenile mortality may explain a left-skewed distribution among individuals of Carneyella ulrichi. Lack of juvenile individuals of S. vorticellatus suggests that this population matured from a single spatfall; there were too few specimens of C. pilea for analysis. Edrioasteroids on this surface exhibit no preferred ambulacral orientation. Spatial analysis (SA) shows an inter-specific clustered distribution at several spatial scales. Intraspecific SA indicates a clustered distribution for Curvitriordo stecki and Carneyella ulrichi; there were too few specimens of S. vorticellatus and C. pilea for analysis. Examination of inter- and intraspecific edrioasteroid taphonomy reveals that thecal collapse, disarticulated cover plates, and disarticulated interambulacral plates occur in nearly half of the population, suggesting brief post-mortem exposure on the paleoseafloor without protection of sediment cover. Individuals of S. vorticellatus suffered thecal collapse, yet all plates and ambulacra remained intact, suggesting that robust thecal elements may inhibit thecal disarticulation.

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