English: Petalodus ohioensis Safford, 1853 - fossil shark tooth from the Pennsylvanian of Athens County, Ohio, USA. (OSU 33552, Orton Geology Museum, Ohio State University, Columbus, Ohio, USA)
This fossil fish tooth is phosphatic - it's composed of apatite (calcium phosphate). It comes from Petalodus ohioensis, a Late Paleozoic shark. The tooth morphology of Petalodus indicates it was a shell crushing shark. Petalodus likely fed principally on calcareous shelled invertebrates such as brachiopods and bivalves.
Classification: Animalia, Chordata, Vertebrata, Chondrichthyes, Petalodontiformes, Petalodontidae
See info. on a Nebraska occurrence at:
gsa.confex.com/gsa/2013NC/webprogram/Paper218747.html