So the other day I found a smooth stone at the what is left of our beaches at lake Huron. In this stone I found what I thought was a quartz vein, until I started carving into it . It turned out to be some sort of fossil with ridges on the inside of the hollowed out bit, pic related. I only carved the stone not the fossil, for some reason my carbide bit slid over it instead of gouging it. Would anyone here happen to know what the fossil is? I thought it was a tooth, but the ridges on the inside throw me off. Also there is a buldge on the back, maybe the root of the tooth, but the position is strange. Open to suggestions.