Paleoecology and taphonomy of two new edrioasteroids from a Mississippian hardground in Kentucky

A recently discovered series of hardground surfaces in the lower Salem Lime stone (Meramecian, Mississippian) and upper Muldraugh Member of the Borden Formation (upper Osagean to lower Meramecian, Mississippian), in Hardin Cou nty, Kentucky is colonized by a hard substrate community that includes thre e species of pyrgate edrioasteroids. Torquerisediscus kypsi n. gen. and n. sp. differs from other edrioasteroids by bearing a cyclic pattern of twelve ambulacral cover plates and meandering distal ambulacra. Ulrichidiscus spi nosus n. sp. differs from other species of Ulrichidiscus by the presence of large spines on the ambulacral cover plates, anal pyramid plates, and hydr opore orals. Two small specimens are assigned tentatively to Ulrichidiscus aff. pulaskiensis. Edrioasteroid populations occurring on several surfaces show marked differe nces in size frequency distribution. Three of the surfaces only have large individuals of Toryuerisediscus kypsi whereas a fourth surface is colonized by only juvenile specimens of T. kypsi as well as both species of Ulrichid iscus suggesting subtle differences in environment and duration of surface colonization prior to burial. Furthermore, taphonomic pathways differ among these four surfaces with some containing only disrupted individuals and ot hers containing only fully articulated individuals suggesting either differ ences in burial depth, or some differences in decomposition of edrioasteroi d carcasses prior to final burial.