8 New Developments and Discoveries in Paleozoic Stratigraphy and Paleontology in the Rocky Mountains and Basin and Range

Tuesday, 12 May 2009
8:00 AM - 12:00 PM

NEW MIDDLE CAMBRIAN EDRIOASTEROID FROM THE SPENCE SHALE OF NORTHERN UTAH

Paper number: 8-2
Program: Theme Sessions
Time: 8:05 AM – 8:25 AM

Authors

Abstract

We are describing a new edrioasteroid genus and species from the upper Spence Shale in northern Utah. The single known calcitic specimen was found by Jamison and is extremely well preserved, although flattened. This specimen belongs to the Order Edrioasterida, which includes edrioasteroids that have a globular to biscuit-shaped theca, pores between their biserial ambulacral floor plates, and in later taxa, a cylindrical, aboral, small-plated collar for attachment. Two other Middle Cambrian edrioasterid occurrences are known from the Rocky Mountains. Several hundred partial specimens of Totiglobus nimius Bell and Sprinkle, 1978, preserved as molds were described from the Middle Cambrian Chisholm Shale of southeastern Nevada. A single weathered calcitic specimen of Totiglobus? lloydi Sprinkle, 1985, was subsequently described from the upper Middle Cambrian Marjum Formation of western Utah, and two additional specimens that may also belong to T.? lloydi were found in the upper Marjum in 1990.

This new Spence Shale edrioasterid seems intermediate between Totiglobus nimius and T.? lloydi by having long ambulacra, large cover plates over the ambulacral floor plates, and relatively few interambulacral plates like the former, but coarsely ornamented cover plates and smaller subsidiaries like the latter. The aboral attachment collar on the new edrioasterid is unlike Totiglobus nimius, which has a fully plated aboral surface with a circular, plated, attachment disk in the center, but is similar to the tapering, tiny-plated, aboral edge of the theca in T.? lloydi. Because of this similarity, T.? lloydi is transferred to the newly described genus as a separate species.

The new Spence Shale edrioasterid lived as a low-level suspension feeder in a muddy, offshore, shelf setting attached to a large Amacephalus idahoense trilobite free cheek on the sea floor with a Gogia sp. theca lying nearby. The slab with these specimens was found in a zone containing numerous, aligned, Gogia sp. thecae that were stalked, mid-level, suspension feeders apparently also attached to trilobite molts or fragments.