Well this was my great grandfathers,and I have no clue what it is!! I remember he always referred to it as the dinosaur heart. I don't know much about where it came from other than it was given to him by a friend years ago. Any information about it would be appreciated!!
I thought turtle shell at first - but symmetry looks off
go to the fossil forum and try and find an expert - you can find other experts by doing a google search
good luck