A CRINOID FAUNA AND A NEW SPECIES OF PYCNOCRINUS FROM THE MARTINSBURG FORMATION (UPPER ORDOVICIAN), LOWER HUDSON VALLEY, NEW YORK

A new crinoid fauna has been discovered in the Upper Ordovician (Katian) Martinsburg Formation at a small shale quarry, locally known as the ‘Shale Bank,’ on the Shawangunk Ridge in Ulster County, NY. The assemblage from a relatively low energy, offshore mud-bottom environment, includes four identified species, including a new species of the glyptocrinid camerate, Pycnocrinus. In order of increasing filter density: the cladid Merocrinus curtus (Ulrich, 1879) with irregularly isotomous and heterotomous, non-pinnulate arms and a stout cylindrical column exceeding 70 cm, the disparids Cincinnaticrinus varibrachialus Warn and Strimple, 1977 with heterotomous non-pinnulate arms, Ectenocrinus simplex Hall, 1847, with extensively branched ramulate arms and meric columns of 460-500 mm, and the camerate Pycnocrinus with uniserial pinnulate arms and a somewhat shorter column. Some round stems with nodose and holomeric columnal specimens are thought to belong to unknown camerate crinoids with pinnulate arms. Filtration theory is used to model food capture in the Martinsburg crinoids. The niche structure of crinoids is basically two-dimensional (e. g., Ausich, 1980). Elevation relative to the seafloor forms the primary dimension, which is dictated by the length of the stem and the nature of the attachment device in Ordovician crinoids. The structure of the arms and their filtration net dictate the nature of the food supply and the current velocities for successful feeding. Surprisingly, even densely pinnulate camerates were able to survive in this setting suggesting that ambient currents attained velocities exceeding 25 cm/sec even in this offshore setting. Similar assemblages were widespread in eastern Laurentia during the Late Ordovician.