A NEW SPECIES OF THE DIVING BIRD, BAPTORNIS, FROM THE LOWER PIERRE SHALE (UPPER CRETACEOUS) OF SOUTHWESTERN SOUTH DAKOTA

Fossil birds are relatively rare in Cretaceous deposits of the Northern Great Plains. From marine deposits of the Niobrara Formation in Kansas, a small diversity of birds is known, but until now, the large diving bird, Hesperornis, was the major bird taxon known from the Pierre Shale of South Dakota. Now, a partial skeleton of another, smaller diving bird, Baptornis, has been secured from the Sharon Springs Member of the Pierre Shale in Fall River County, South Dakota. The specimen is represented by pelvic fragments and lower leg elements that similar to but much more robust than Baptornis advena from the subjacent Niobrara Formation. The taxon is nearly twice the size of the Niobrara species, principally in robustness rather than length of elements. Overall, the specimen represents the first occurrence of Baptornis from the Pierre Shale, represents a new species, and indicates a greater diversity of birds from the Pierre Shale than previously thought.