THE OLDEST SHRIMP (DEVONIAN: FAMENNIAN) AND REMARKABLE PRESERVATION OF SOFT TISSUE

Discovery of a single specimen of a shrimp fossil from the Devonian Woodford Shale in the Ryan Quarry, near Ada, Oklahoma, documents the oldest occurrence of a penaeoid decapod crustacean. The specimen lacks diagnostic features of the Superorder Eocarida, including caudal furca, but possesses the characteristic form and preservational style of the Superorder Eucarida, particularly the Superfamily Penaeoidea. The fossil is associated with a marine fauna including conodonts and ammonoid cephalopods that constrain the age of the unit. A previous report of arthropods from the Woodford Shale (Cooper 1932) included a phyllocarid, Concavicaris, and a form of uncertain affinities assigned to the genus Sidetes Giebel, 1847, that is now considered to be an ammonoid aptychus and not an arthropod. The shrimp specimen is remarkably preserved; it has been phosphatized, and the abdominal muscles have been preserved completely enough that discrete muscle bands are discernable. The cuticle of the cephalothorax is shattered into small fragments, whereas that of the abdomen is absent except on the telson. Confirmation that this specimen represents a Devonian decapod documents only the second decapod taxon known from the Devonian and the third from the Paleozoic. It is the earliest known shrimp and one of the two oldest decapods, both from North America. The common ancestor may lie within the North American Eocarida. Supported by NSF EF0531670 to Feldmann and Schweitzer.