Middle Turonian (Late Cretaceous) rudistids from the lower tongue of the Mancos Shale, Lincoln County, New Mexico

Abstract

Rudistids are uncommon fossils in Upper Cretaceous rocks of the Western Interior of the United States. Since 1856 there have been fewer than 40 occurrences noted in the literature, many of these without descriptions or illustrations. Only six of these occurrences are from New Mexico. Therefore, the discovery of two fragments of solitary radiolitid rudistids and one fragment of a small bouquet from a sandy concretionary bed in the lower tongue of Mancos Shale in Lincoln County, New Mexico, is of some importance. Associated fossils in the concretions include the ammonites Spathites rioensis, Morrowites depressus, and Collignoniceras woollgari woollgari, placing the rudistid bed in the lower part of the middle Turonian C. woollgari Zone. Although specifically indeterminate, the rudistids are probably conspecific with a large rudistid bouquet composed of Durania cornupastoris that was described and illustrated from rocks in the same zone in the Greenhorn Limestone of Colorado.