Hi all   My kids and I found this tooth a while ago from the North Sulphur River in Texas. We can't figure out its ID and would appreciate any help.  There is no carina; however, there are deep groves at the base.  It appears cylindrical.  After looking at various images, I can't tell if this is from a fish or a marine reptile like at plesiosaur.  Images are below; the scale is 1 mm between the smaller hashmarks.    Again, thanks for any help! Bret