Post Oak Creek unidentified tooth.

[Austin83]

As usual, we found the usual shark teeth in Post Oak Creek in Grayson County, but I’m unsure about this tooth.  I’m very new at this, but it doesn’t have a flat backside like the typical shark tooth that we find, but it is almost a perfect oval shape. Any help is greatly appreciated.  Have a great day! 

[Austin83]

After looking around on the internet, it looks similar to a tooth from a Xiphactinus?

[jikohr]

It's almost certainly fish. I'm also leaning toward Xiphactinus, but let's see what someone more experienced with him says.