FOOT-LONG PHYLLOCARIDS: LARGE ARCHAEOSTRACANS (PHYLLOCARIDA) FROM THE BORDEN FORMATION (MISSISSIPPIAN, OSAGEAN) OF KENTUCKY

Phyllocarids are rare faunal elements of the Upper Paleozoic. Previous reports of phyllocarids from Kentucky include the occurrence of Dithyrocaris from the Pennsylvanian Breathitt Formation of northern Kentucky and the occurrence of Ceratiocaris (Colpocaris) (= Concavicaris) bradleyi from the Mississippian Borden Formation at Danville, central Kentucky. The latter is no longer considered a phyllocarid.

We report authentic phyllocarids from the Nancy Member of the Borden Formation of northeast Kentucky. These archaeostracan phyllocarids are represented by well-preserved mandibles and caudal elements, partial remains of abdominal segments, and a ceratiocaridid-like rostrum. The mandibles are represented by three large, sclerotized specimens, two of which may be corresponding left and right mandibles, and both of which show large portions of the mandibular body. The mandibles are arcuate, with at least seven denticles. Two mandibular fragments are perforated by 1–2 mm tubular burrows; smaller branching burrows are present on two mandibles near and on the gnathal lobe. Abdominal segments are mostly smooth, or marked with distinct terrace-like ridges and some subtle, low, short, curved, finer, ridge-like ornamentation. The telson has long, slender, telson spines marked with longitudinally oriented, terrace-like ornamentation. An enigmatic (?)appendage with a bifurcate termination is preserved with abdominal fragments alongside one of the telson spines.

Based on independent estimates utilizing the size of the mandibles and the size of the telson, these phyllocarids were up to 30 cm in total body length. These are the largest known marine arthropods from the Mississippian of Kentucky.