I heard that ancient clams had teeth, is that true?

Information on the subject is scant.  This is because most clams when they died did not become dinosaur bones, like the dinosaurs.  They became limestone.  That is not to say that all dinosaurs became bones, some became oil, which was then turned into bags, which can be used when buying model dinosaur skeletons at gift shops, thus completing the circle of life.  Limestone is made of calcium (calcium carbonate), and teeth are made of calcium (calcium phosphate), so it is obvious that clams are completely capable of having teeth.  Heck, they basically half teeth all ready (calcium for you slower folks)!

On a side note, be sure that you are getting enough calcium in your diet, or your normal eating if you are satisfied with your current weight.  Dairy is a great source of calcium.  That is why baby teeth are sometimes referred to as "milk teeth."

I did some research on the subject of clams and discovered the following; one poem ( here), and one brief reference in a letter to the Smithsonian (here).  The page being referenced has it labeled as an urban legend, and as being false.  Clearly they did not do enough research, or they would have found the poem, which corroborates the story of the clams having teeth.  It is well known that poems never lie. 

For example "The fog came in on little cat feet." It is true, but it is a big cat for such little feet.  Or "There once was a man from Nantucket..."  Well, probably shouldn't bring him up here.  So, moving on with the examples "Two roads diverged in a yellow wood, and sorry I could not travel both, and be one traveler..."  Well, this may in fact prove to be erroneous with the continuing work on entwined elementary particles, but needless to say, the afternoon stroll that Robby Frost was on at the time would hardly be the time to be carrying around the necessary equipment to perform such actions.  Not to mention that the ramifications of such an act would be huge.  Currently stem cells are controversial, imagine that research.  It would be like better than a clone, because the entwining would cause each clone to experience the same things.  Of course, there are down sides, like if one of you dies...  More research also needs to be done to see if each entity could move apart without an external force.  It seems logical that each would be required to step at the same time, trip at the same time, etc.  I wonder what would happen to the one of them if the other were to be eaten by a ravenous man eating clam, with big teeth.  Note to self, think more on this later, much later, it gives me a headache.)

Well, I hope that proves it.  Clams had teeth.  The mystery is why would they give up such an evolutionary advantage.  It would also be a good time to be thankful that they never grew legs, otherwise we may still be on their diet, except those of us with high cholesterol, we would be safe, we would clog their arteries.