“PALEOECOLOGY OF JURASSIC ENCRINITES” RECONSTRUCTING CRINOID COMMUNITIES FROM THE JURASSIC OF THE WESTERN INTERIOR SEAWAY

Articulated Jurassic crinoids, relatively common in Europe, are rare in North America. The few that have been described are simply, and incorrectly, labeled ‘Pentacrinus'. The Jurassic crinoid community of North America consequently remains poorly known. However, encrinites (rock chiefly composed of crinoid debris) are surprisingly common in North America, and represent some of the best examples of post-Paleozoic accumulations known. These rocks are highly significant for understanding the early ecology of isocrinid crinoids, and provide an insight into the wider crinoid communities of North America. A previous study of the encrinites of Utah revealed the great potential of these sediments for our understanding of crinoid palaeocommunities, however such treatment has not been applied across all of the crinoid faunas in North America

Following reanalysis of Jurassic crinoids of the Western Interior Seaway, a number of non-endemic forms are reported, together with highly specialized crinoids. The encrinites (chiefly from the Bathonian) are diverse, with distinct marine and lagoonal communities recognized. These diverse ecological associations are comparable to those seen in contemporaneous European Jurassic. Many of the classic European genera are recorded, examples include early Jurassic forms such as Seirocrinus subangularis from the Fernie Formation Alberta, Canada and Isocrinus from the Oxfordian/Callovian of the Sundance Formation Wyoming, United States.

This new data, and existing data from the Jurassic shallow seas of Europe, demonstrate that crinoid distribution patterns are largely facies influenced, geographical factors being of limited importance. Even within the same region, taxa in lower energy off-shore facies contrast strongly with those found in more restricted facies. Yet comparable facies in North America and Europe are characterized by very similar crinoid communities.