The 1st claw of the Utahraptor was thought to be a rib--they grew 'em big in this period, from Latin for "chalk"
The Sloth Claw [DOC] [TLE] PALAEOBLOG: May 2006 [PAR] May 31, 2006 ... Then, using fossils and genetic data, they looked at rates of DNA evolution and 
speciation during a 30-million-year period in foraminifera plankton, ... the 2.5 km 
cave's surface is situated under a layer of chalk that is impenetrable to water.