REVIEW OF THE ACTINOCRINITIDAE FROM THE MISSISSIPPIAN (VISEAN) FORT PAYNE FORMATION OF KENTUCKY

The recent comprehensive review of the Family Actinocrinitidae (Rhenberg et al., 2015) has clarified the poorly understood genera of this very important Mississippian crinoid family. The Mississippian Fort Payne Formation (Visean) of Kentucky is a good example of a fauna that was previously considered to have only contained Actinocrinites. After a comprehensive review of the Fort Payne actinocrintiids, we now recognize two genera and at least six species.

The Fort Payne formed near the toe of the slope of a clinoform and consists of both siliciclastic and carbonate facies (Greb et al., 2008). The siliclastic deposition was punctuated by carbonate mound buildups, presumably during a short-duration rise in sea level. Actinocrinitids live principally on carbonate buildups. Of the specimens found in our collection, which we believe to be representative of the formation’s actinocrinitids, Actinocrinites jugosus remains the only identifiable species of that genus in the Fort Payne. The rest of the reported actinocrinitids fall into the genus Thinocrinus: T. c.f. botruosus, T. gibsoni, T. lowei, T. probolos, and T. sp. nov. Thinocrinus gibsoni and T. probolos have not been previously identified as being in the Fort Payne. Thinocrinus tripus, which has been previously reported from the Fort Payne, is suspected to be a junior synonym of T. gibsoni. Thinocrinus sp. nov. is distinguished from the other actinocrinitids, both in the Fort Payne and other formations, by possessing unique spiny plates that appear to separate the calyx from the tegmen in the interray area. The spines, of which there could be between three and five, protrude outward from the center of the body, presumably between each of the regular interrays and perhaps on the posterior interray, but that is unknown.