XANTHOSIA OCCIDENTALIS BISHOP, 1985, AND XANTHOSIA SPINOSA, NEW SPECIES, TWO LATE CRETACEOUS CRABS FROM THE PIERRE SHALE OF THE WESTERN INTERIOR

Abstract

ABSTRACT A finely preserved specimen of Xanthosia elegans occidentalis Bishop, 1985, from the early Campanian Gammon Ferruginous Member of the Pierre Shale collected from the Heart Tail Ranch Association, Butte County, South Dakota, allows elevation of the subspecies to specieslevel rank and allows its comparison with Xanthosia elegans Roberts, 1962. Xanthosia occidentalis, new species, is judged to have been an active swimming crab. Because of the inferred swimming mode of life, relative stratigraphic positions of species of Xanthosia to younger portunid crabs, and the overall remarkable similarity of Xanthosia to portunid crabs, Xanthosia is suggested as a likely ancestor to the Portunidae. A second species, Xanthosia spinosa, new species, is described from the Pierre Shale (upper Campanian) of Grand County, Colorado.