Kenshu Shimada would be the person to contact in regard to the shark fossil. The latest address I have is the University of Illinois,Dept of Biol Sci (M/C 066) 845 West Taylor Street, Chicago, IL 60607-7060,Fax:(312)413-2435. He has done a lot of work with Niobrara sharks down at the Sternberg Museum in Kansas. If this fails, contact me and we'll try to find him.